1 Overview

In mid 1998 I set up a home network. Was starting a consulting business and wanted to learn about building and operating a Small Office Home Office (SOHO) network. My prior networking experience was limited to interactions with corporate Information Technology (IT) department.

LAN has undergone significant evolution over the years. It started with Dialup Internet access and a few 10 BaseT Ethernet drops. Over the years it expanded beyond my home office to encompass the entire house and upgraded to 100 BaseT Fast Ethernet. 1500/384 DSL replaced dialup as the Internet connection. Initially we used Wingate connection sharing software and BlackIce Defender for intrusion detection running on a dedicated laptop to share dialup connection. When we got DSL laptop was replaced with a MultiTech router connected to DSL modem. That has since been replaced with a Netopia (now part of Motorola) 3346 DSL/Router. A recycled desktop serves as a poor mans server. In addition to file sharing it runs: TreeWalk DNS resolver, Tardis network time service, Abyss local web server and Kiwi Syslog log server. Each PC normally requires its own monitor, keyboard, and mouse. Rather then use separate I/O devices for server and desktop we opted to use a Belkin KVM (Keyboard Video Mouse) switchbox. This allows a single keyboard, mouse and monitor be shared by workstation and server. Having a KVM make it easy to temporally connect additional systems for setup and testing. A HP 550 ink jet printer is networked and accessible from any PC on the LAN.

Traveling with a Laptop can be a challenge: as network configuration differs at each location. NetSwitcher automates this task providing one click switching between locations.

We use Acronis for automatic on line back up to the server. A CD/DVD burner provides off line backup.

This paper is not intended as a competitive product review. The field is constantly changing; any attempt to do so quickly becomes outdated. Rather, it discusses how specific requirements were addressed. For up to date product reviews the interested reader is directed to the many publications and articles on the subject. Products and services described in this paper represent my choice to deliver the features I need.

Goals for SOHO network:

Share broadband Internet service
Share Printer
Local file sharing
Local internal web server
Secure remote access to corporate network
Access multiple e-mail accounts
Access to USENET newsgroups
Fax without a fax machine
Automatic time synchronization
Automatic file backups
Display home weather station data
Learn networking

This paper discusses Internet access and connection sharing options. Even a small network benefits from having an always-on server. Structured wiring techniques for telephone and Ethernet are covered in detail. Security and Troubleshooting topic helps maintain network and protect it from intruders.

Last topic discusses registering a domain name and running a public server. Every business ought to have an Internet presence. It does not take much effort to set up a simple web site and cost is low.

2 Internet – Much More Than World Wide Web

The Internet began life 40 years ago as a means for government and academics to share expensive mainframe computers. Today it is the preferred method used to access all sorts of digital media: data, voice and images. Internet is a contraction of Inter Network, literally a network of networks. Creation of the Word Wide Web in the 1990’s vastly expanded Internet popularity by providing a Graphical User Interface (GUI) on what until then been a text based communication network. Some equate World Wide Web with the Internet. The two are not synonymous. The web is simply one, admittedly a very popular, application supported by the Internet.

2.1 ISP

Internet Service Providers (ISP) connect end users to the Internet. Internet popularity is driving demand for high-speed low cost service. High-speed Internet access is becoming widely available. Even though we are in a fairly rural area broadband is available from three sources 1) Cable company 2) Telco 3) Competitive Local Exchange Carrier (CLEC) that rent copper phone line to deliver DSL. We currently have 1500/384 kbps ADSL service provided by Verizon On Line.

For a more detailed examination of ISPs interested reader it referred “First-Mile Access” paper on the writings page.

2.2 Services

The Internet transports data from one host to another over a common network shared by many other users.

New comers often equate the World Wide Web (WWW) with the Internet. WWW is simply one of many Internet services. WWW uses HTTP, Hyper Text Transport Protocol to display web pages.

Other popular services:

DNS - Domain name system acts as an Internet directory service translating host names to IP addresses.

FTP - File Transport Protocol an efficient protocol used to exchange files.

IGMP - Internet group management protocol enables a single server to simultaneously send data to many users, much like over the air transmission.

Instant Messaging - is a popular digital information exchange protocol that allows people to conduct real time chat sessions.

IPTV – is a collection of protocols and services to deliver TV/movies over the Internet. IP radio is already popular. Lack of high-speed first-mile service and concerns over copyright in a digital world are limiting deployment of IPTV. As first-mile access speed increases it will be possible for anyone to deliver “cable TV.”

NNTP - Simple Network News transfer protocol is the bases for Usenet

POP - Post Office Protocol and SMTP Simple Mail Transport Protocol provides email services. IMAP, Internet Message Access Protocol is an advanced email format used by some ISPs.

SIP – Session initiation Protocol is used to setup and teardown Internet phone calls. RTP – Real-time transport Protocol is used to deliver packetized voice.

SNTP – Simple Network Time Protocol distributes accurate time information.

VoIP – Voice over IP is an emerging technology that uses packet based Internet transport for telephone calls. This is part of digital convergence using the Internet to carry many different types of traffic as opposed to creating a purpose built network for each service.

2.3 Latency vs Speed

Non technical folks often confuse latency with speed. Latency is how long it takes a packet to get from location A to B. Speed is rate bits are transmitted across the network. A useful analogy is the think of a truck full of DVDs going from Point A to B. From the time the truck begins its journey latency is high – while truck travels to the destination recipient can do nothing. However once it gets there speed is very high due to the tremendous capacity of the DVDs.

Conversely a dialup connection has low latency since data arrives milliseconds after it is requested. Speed on the other hand is low – limited by switched telephone network performance. For a more in-depth explanation see “It’s the Latency Stupid.”

2.4 Naming Convention

Domain names provide a friendly handle to access a resource rather than using IP addresses directly. Domain names are hierarchal evaluated right to left. The highest-level of the tree called Root is implied. Next is the top-level domain (TLD) these are the COM, EDU, ORG, MIL and GOV of the world. As the Internet expanded each country was assigned a unique two-letter top-level domain. For example the TLD for the United Kingdom is UK. Within each domain various agencies are responsible for name registration, called registrars. The role of the registrar is to insure each registered name is unique within a top-level domain. For example in our case the schmidt.com domain was already assigned so we picked tschmidt.com.

Often an organization creates sub domains such as www.tschmidt.com for web access, mail.tschmidt.com for mail or product.tschmidt.com for product info. Since the domain name is registered and guaranteed to be unique the domain owner is free to add as many sub domains as desired.

2.4.1 Domain Name Service (DNS)

When a domain is registered the registrar database contains the nameservers that provide authoritive information about the site. Authoritive nameservers are managed by the site administrator and contain all the information necessary to access the various servers within that domain.

When a Uniform Resource Locator (URL) is entered into the browser, such as http://www.google.com/, the browser first checks to see if this is a local host. Windows name resolution looks in the Hosts file to see if an address has been entered manually then it uses NetBIOS over IP to search local machines on the LAN. This is a broadcast mechanism and works well on small LANs but does not scale well. If host is not found the translation request is passed to the DNS Resolver.

Lets trace what happens when we looking up www.google.com. Since the request is not local it is passed to the DNS system. The highest level is root. The naming hierarchy includes an implied dot (.) to the right of the TLD this is called the root. The DNS Resolver is preprogrammed with the IP address of several root nameservers. The request goes to one of the root nameservers that returns the address of the nameserver for the .COM top-level domain (TLD) since Google is in the COM TLD. Then the COM nameserver is quired for the address of Google nameserver. The server returns the address of the authoritive nameserver for the Google domain. It is important to note root nameserver does not know address of any Google servers other then the Google nameserver. The Google nameserver is then asked for the address of the desired host and the nameserver returns the address. Often sites create sub domains for specific server, the process continues until the address of the desired host is determined. Once the browser has the IP address it is able to communicate with the desired host. This is a very superficial view of how DNS works. For a more in-depth view see DNS Complexity by Paul Vixie.

Obviously going thought this multistep process each time one needs to translate a URL is rather time consuming. To speed up the process DNS resolvers cache recently used information. DNS records have a time to live (TTL) parameter indicating how long cached information may be used before it must be refreshed. Name lookup is normally accomplished in a few milliseconds.

2.5 Routing

Internet is a routed network. This is very different then the broadcast discovery scheme used locally by Ethernet or circuit switching used by the legacy telephone network. When a computer wants to communicate with a resource not available locally it forwards the packet to a gateway router. Routers forward incoming packets to the proper destination or to the next router in the chain. To learn network topology routers use a variety of techniques to communicate among themselves such as RIP and OSPF. ISP routers know how to forward incoming packets to customers and customer originated packets to the Internet backbone. Each router in the chain forwards packets closer to the destination until the packet ultimately arrives at its destination. It is not uncommon to have ten to twenty hops between sender and destination.

2.6 Multicast

Most Internet traffic is 1:1 (unicast); a host communicates directly with another host. Multicast emulates traditional broadcast 1:many. This is more efficient way to stream information to many endpoints. Unfortunately even though specifications exist to support it not many ISPs have implemented multicast. In general if you listen to Internet radio or TV it is being done over unicast.

2.7 Quality of Service (QoS)

Packet based networks are egalitarian best effort networks. This works amazing well for transferring large chunks of data from point A to point B. The network functions in the presence of all sorts of impairments and failures. However: best effort does not work as well with latency critical applications such as telephony and streaming media. When a switch or router encounters congestion it buffers incoming packets until it is able to forward them. Quality of Service (QoS) metrics allows latency critical data to go to the head of the line. This simple strategy works well if latency critical traffic is a small percent of the total so bumping its priority has little negative effect on other traffic.

Given the low cost and high speed of consumer Ethernet equipment few QoS problems occur on wired Ethernet LAN. Wireless LANs are slower and subject to radio interference benefit from QoS. Where QoS is most important is uploading to the Internet. Most consumer broadband links have relatively little upload capability. QoS is a great help in managing this limited resource.

2.8 TCP Slow Start – Receive Window – et al

When a host begins transmission it has no idea how fast the intervening links are between it and remote host. To address this issue transmitter begins sending a few packets waiting for acknowledge. The faster ACK arrive the more packets the transmitter sends per unit of time.

2.9 IP Address

Each IP device (host) must have an address. Addresses may be assigned, statically, automatically by DHCP (Dynamic Host Configuration Protocol) or automatically by the client itself, AutoIP. Traditionally a system administrator manually configured each host with a static address. This was laborious and error prone. DHCP simplifies the task by automating address allocation. The down side is need for a DHCP server. DHCP has been extended to allow automatic configuration if host cannot find a DHCP server. In that case device assigns itself an address from the AutoIP address pool. AutoIP is convenient for small LANs that use IP and do not have access to a DHCP server. This occurs most commonly when two PC’s are directly connected.

The current Internet protocol is version 4. Each host is assigned a 32-bit address, resulting in a maximum Internet population of about 4 billion hosts. Due to IPv4 address scarcity it is common practice for ISPs to charge for additional addresses. Address exhaustion has been a concern for a long time. Several techniques have been developed to minimize address consumption. Next generation IP, version 6, expands address space to 128 bits. This is a truly gigantic number. While IPv6 holds much promise it entails wholesale overhaul of the Internet. Such change is always resisted until one has no choice to go through the pain of conversion.

2.9.1 Dotted-Decimal Notation

Internet addresses are expressed in dotted decimal notation, four decimal numbers separated by periods, nnn.nnn.nnn.nnn. The 32-bit address is divided into four 8-bit fields called octets. Each field has a range of 0-255. The smallest address is 0.0.0.0 and the largest 255.255.255.255.

2.9.2 Subnet

IP addresses consist of Network-Prefix and Host address. Subnetting allows IP addresses to be assigned efficiently and simplifies routing. The subnet mask defines boundary between network and host portion of address. Hosts within a subnet communicate directly with one another. Hosts on different subnets use routers to forward packets from one subnet to another.

In our network all computers are on a single subnet. Our network uses subnet mask of 255.255.255.0 allowing up to 254 hosts (computers) also called a /24 subnet because the first 24-bits of the address are fixed. Host addresses are allocated from the last octet (8-bits). The reason for 254 rather than 256 hosts is the lowest address is reserved as the network address and the highest address for multicast.

2.9.3 Class vs Classless Inter-Domain Routing (CIDR)

When the Internet was initially developed the divide between network prefix and host address was embedded within the address itself, rather then set by a subnet mask. These were called address classes, lettered A – E.

Class A – first octet is in the range 1 – 126 (0XXXXXXXb). 8-bits reserved for network portion leaving 24 for host addresses. 24-bits provides 16,777,213 host addresses. The lowest address is reserved as the network address, highest for broadcast. NOTE: first octet of 127 is reserved for test purposes.

Class B – first octet is in the range 128 – 191 (10XXXXXXb). 16-bits reserved for network portion leaving 16 for host addresses. 16-bits provides 65,533 host addresses.

Class C – first octet is in the range 224 – 249 (110XXXXXb). 24-bits reserved for network portion leaving 8 for host addresses. 8-bits provides 254 host addresses.

Class D - first octet is in the range 224 – 239 (1110XXXXb). Class D networks reserved for multicasting.

Class E - first octet is in the range 240 – 255 (1111XXXXb). Class E networks reserved for experimental use.

It became clear very early that allocating addresses this way was very inefficient. Class C was too small for many organizations and Class A too large. Classless Inter-Domain Routing (CIDR) was developed to allow network prefix be fixed at any bit boundary. CIDR using variable submask is now universal and Class based routing of historic interest, although one still hears reference to Class A, B, and C networks.

2.9.4 Port Number

Internet host are able to carry on multiple simultaneous communications sessions. This raises the question how does the computer know how to respond to incoming packets? While writing this paper my mail program is checking e-mail every few minutes, I’m listening to a web based radio program and from time to time getting information from a multitude of web sites. Each TCP or UDP packet includes a port number. Port numbers are 16-bit unsigned values that range from 0-65,535. The low port numbers 0-1023 are called well-known ports; they are assigned by IANA the Internet Assigned Number Authority when a service is defined. Software uses the well-known port to make initial contact. Once connection is established high numbered ports are used during the transfer. For example: when you enter a URL to access a web site the browser automatically uses port 80. This is the well know port for web servers.

2.9.5 Private Address Block

During work on the impending IPv4 address shortage RFC 1918 reserved three blocks of private addresses that are guaranteed not used on the Internet. Private addresses are ideal for our purposes. Internal hosts are assigned an address from the RFC 1918 pool. Private addresses are not used on the Internet. This allows them to be used and reused without risk of colliding with Internet hosts. This eliminates need and expense to obtain a block of routable addresses from the ISP. To connect LAN to Internet the router, or connection sharing software, uses a technique called Network Address Translation (NAT). NAT converts the private LAN IP addresses public address assigned by the ISP.

Excerpt from IETF RFC 1918 Address Allocation for Private Internets:

Internet Assigned Numbers Authority (IANA) reserved the following three blocks of the IP address space for private Internets:

10.0.0.0 - 10.255.255.255 (10/8 prefix)

172.16.0.0 - 172.31.255.255 (172.16/12 prefix)

192.168.0.0 - 192.168.255.255 (192.168/16 prefix)

We will refer to the first block as "24-bit block", the second as

"20-bit block", and to the third as "16-bit" block. Note that (in pre-CIDR notation) the first block is nothing but a single class A network number, while the second block is a set of 16 contiguous class B network numbers, and third block is a set of 256 contiguous class C network numbers.

An enterprise that decides to use IP addresses out of the address space defined in this document can do so without any coordination with IANA or an Internet registry. The address space can thus be used by many enterprises. Addresses within this private address space will only be unique within the enterprise, or the set of enterprises which choose to cooperate over this space so they may communicate with each other in their own private Internet.

2.9.6 AutoIP Address Block

A fourth block of private IP addresses is reserved for AutoIP. If a host is configured to obtain a dynamic address and a DHCP server cannot be found the host assigns an address to itself from this pool of reserved addresses. The host picks an address from the AutoIP address pool, and tests to see if it is already in use by trying to contact that IP address. If the address is not in use it assigns itself the address. If the address is in use it picks another at random and tries again.

AutoIP address block:

169.254.0.0 - 169.254.255.255 (169.254/16 prefix)

AutoIP is extremely useful for tiny networks that do not have a DHCP server. Before AutoIP the user had to manually configure IP addresses to set up a simple network.

2.9.7 Local Host Address

127.0.0.1 is the loopback address. This is useful for testing to makes sure the network interface is working. Sending data to the loopback address causes it to be received without actually going out over the physical network.

2.9.8 Multicast Address Block

IP sessions are typically one to one, host A communicates with host B. It is also possible for a host to broadcast to multiple hosts. IANA reserved several address blocks for multicast.

Multicast address block

224.000.000.000 – 239.255.255.255 (224/8 – 239/8 prefix)

2.9.9 Address Resolution Protocol (ARP)

IP addresses represent the global numbering scheme of the Internet. The addressing scheme used by the physical network is different. For example Ethernet uses a 48-bit MAC address. ARP provides a mechanism to learn MAC address associated with a particular IP address. Reverse ARP (RARP) determines if an IP address exists for a particular MAC address.

2.10 Terminology

As with any specialty the Internet has its share of technical terms and acronyms. Here are some of the most important.

Address – 32 bit (IPv4) or 128 bit (IPv6) host address. Except for certain exceptions (private addresses) each address on the Internet must be unique. Example of an IPv4 address: 198.245.39.4, IPv6 address: FEDC:BA87:200C:4267:FFFE:1080:0003:0016

ARP – Address resolution protocol is used to translate IP address to Ethernet MAC address.

AutoIP – Enhancement to DHCP allowing a host to self-assign an IP address if it cannot find a DHCP server.

DHCP – Dynamic Host Configuration Protocol automatically configure network hosts with IP settings.

DNS - Domain Name System translates host name: such as www.tschmidt.com to IP address 207.121.124.46.

Domain Name – Hierarchical naming structure used on the Internet. The highest level is root, then top-level domain such as .COM, .EDU, .NET .UK etc, next the registered domain name, such as Google. Then sub domains such as mail or www as in mail.google.com or www.google.com.

Dotted Decimal Notation - for ease of representation 32 bit IPv4 addresses are broken down into four groups of 8-bits. 8-bits can represent any value from 0-255. 192.168.1.5 is a typical IPv4 address.

DUN – Dial Up Networking is a suite of tools to allow a computer to access an ISP over low speed dial up link.

FTP – File transport Protocol

Gateway – Another name for router used to forward packets between networks.

HTTP – Hyper Text Transport Protocol – used to exchange Web data.

ICMP - Internet Control Message Protocol, handles control function such as PING. PING verifies a remote host is reachable and how long it takes.

IGMP – Internet group management protocol enables a single host to communicate with multiple computers emulating the one-to-many broadcast of over the air transmission.

IM - Instant messaging is a very popular digital information exchange protocol allowing many users to interact in real time chat sessions. Unfortunately IM has evolved outside the IETF standards process with each vendor creating incompatible formats and jealously preventing interoperability.

IMAP – Internet Message Access Protocol

IP – Internet Protocol

IPv4 – Current Internet protocol. A 32-bit address is assigned to each host. The LAN uses a reserved block of private addresses that can be reused multiple times. IPv4 provides about 4 billion IP addresses.

IPv6 – Next generation IP. The most notable change increases the address space to 128 bits, eliminating the current addressing shortage and opening to door to new applications.

MAC address – 48-bit Ethernet end point address assigned by Ethernet hardware vendor. MAC address is split into two portions, vendor ID (assigned by IEEE) and serial number identifying the specific device.

NAT – Network Address Translation is used to translate one set of IP addresses to another. NAT is used extensively on small residential networks allowing multiple hosts access a single ISP account while using only one public IP address. Network Address Port Translation (NAPT). A more accurate term for translation technique used with small routers. In order to share a single public address with many local private addresses NAT translation needs to include port translation.

NNTP – Network News Transfer protocol.

OSPF - Open Shortest Path First is a router communication protocol allowing routers to exchange network topology information.

POP – Post Office Protocol

Port – 16-bit value used to distinguish amount multiple simultaneous connections to a single host.

Private IP address – Blocks of IP addresses reserved by IANA for private use. Private addresses are not assigned to hosts on the public Internet. This allows the addresses be reused multiple times.

QoS - Quality of Service treats packets differently based on latency requirements.

RIP – Routing Information Protocol. Early router communication protocol: see OSPF.

Router – Interconnects two or more networks. Makes forwarding decisions based on destination IP address.

RTP – Real-time transport Protocol is used to deliver packetized voice.

SIP – Session Initiation Protocol is used to set up and tear down Internet phone calls.

Slow Start – TCP control mechanism to address congestion and slow network links.

SMTP – Simple Mail Transport Protocol

Sub Domain – lowest level in domain hierarchy, such as: www. The domain owner can create as many sub domains at they want.

Subnet Mask – Binary mask used to define boundary between network and host portion of addresses. Within a subnet hosts are directly accessible, communication does not require a router. Communication to a different subnet requires a router. For example a Subnet mast of 255.255.255.0, also called a /24 address, has 24-bits allocated to the network portion and 8 –bits reserved for hosts.

TCP - Transmission Control Protocol, TCP is an end-to-end transfer protocol that recovers from transmission errors and is responsible for reordering packets that arrive out of order. When an application creates a TCP/IP connection the receiver sees the same data stream as was transmitted.

TLD – Top Level Domain – highest level of the domain naming hierarchy such as: .COM, .EDU, .NET, .UK etc

UDP - User Datagram Protocol is a connectionless protocol; it is used when end-to-end synchronization is not required. The transmitting station casts packets out to the Internet. Each packet is dealt with individually. UDP is often used with multimedia. If a packet is lost it cannot be retransmitted in time so receiver has to fake the missing information.

URL - Uniform Resource Locator, human readable host name.

VoIP – Voice over IP Use packet technology to carry voice calls rather then traditional circuit switching.

Well Known Port – used to establish initial connection. For example: the well-known port for web servers is TCP port 80.

WWW – World Wide Web Graphical information system based on hypertext.

3 Local Area Network (LAN) – Networking for Everyone

Local Area Network (LAN) allows computers to access shared resources such as printer, files, and the Internet. Ethernet, both wired and wireless, dominates SOHO network market.

3.1 Ethernet

Wired Ethernet IEEE 802.3 is the most common local network technology in use today. It was initially based on CDMA/CA (Collision Detection Multiple Access Collision Avoidance). Think of Ethernet as a telephone party line. Before speaking listen to see if anyone is talking. If no one is talking it is OK to start. It is possible more then one person may start talking at the same time. That is a collision; no one is able to understand what is being said. When this occurs everyone stops talking for a while. When the line is idle they try again. Each party waits a different length of time to minimize odds of colliding again. CDMA/CD imposes a number of constraints to network design. Minimum packet size must be longer than the end-to-end propagation delay of the network. This insures the transmitter is still transmitting when the collision occurs allowing retries to be done at the data link layer. Power level and end-to-end loss budget must be set to allow reliable collision detection.

When Ethernet was originally developed it operated at 10 Mbps and used fat coax cable with clamp on taps, called vampire taps. Early development focused on improving physical interconnection rather then speed. Specification evolved from Fat coax, to thin coax to twisted pair. Today most common type of Ethernet is unshielded twisted pair (UTP) copper cable consisting of 8 conductors organized as 4 pairs terminated with 8 conductor modular jacks similar to those used for telephone wiring. Since its inception speed has dramatically increased from 10 Mbps (1980) to 100 (1995) to 1G (1,000 Mbps) (1998), 10G (2002) work is under way on 40G and 100G Ethernet. Ethernet Switches have replaced hubs eliminating collision domain permitting full duplex operation.

As speed increases fiber becomes the preferred choice. The difficulty with fiber is not so much fiber cost but high cost of opto-electrical converters needed to connect NICs to fiber cable.

3.1.1 Media Access Controller (MAC) Address

Each Ethernet interface (wired or wireless) has a unique address called the MAC address. This allows each interface to be uniquely addressed. This is not the same as the IP address. MAC vendor ID is assigned by IEEE.

Excerpt from Assigned Ethernet numbers:

Ethernet hardware addresses are 48 bits, expressed as 12 hexadecimal digits (0-9, plus A-F, capitalized). These 12 hex digits consist of the first/left 6 digits (which should match the vendor of the Ethernet interface within the station) and the last/right 6 digits which specify the interface serial number for that interface vendor.

These high-order 3 octets (6 hex digits) are also known as the

Organizationally Unique Identifier or OUI.

These addresses are physical station addresses, not multicast nor

broadcast, so the second hex digit (reading from the left) will be even, not odd.

3.1.2 Virtual LAN (VLAN)

Virtual LAN technology allows the same physical LAN to connect multiple computers while isolating one group from another. Typical use is to create separate VLANs based on community of interest for example payroll, marketing and engineering. A router is used to interconnect the domains providing a great deal of control over how data flows across VLAN boundaries.

VLANs are not yet common for home LANs but may become so if Internet services are delivered by multiple service providers, perhaps one for data, another for IP based TV (IPTV), and yet another offering Voice over IP (VoIP).

3.1.3 Universal Plug and Play

UPNP is an outgrowth of PC plug and play experience designed to automatically configure local network devices. As this paper should make clear configuring a LAN can be a daunting task requiring user to be conversant with network terminology and concepts. UPNP provides automatic discovered and when needed request firewall/router to adjust configuration to allow the particular service Internet access.

Unfortunately UPNP makes no provision for security so one has no knowledge or control of malicious devices attempting to gain unauthorized access to the Internet. If you are unfamiliar with network configuration and confident PCs have not be compromised then UPNP is very convenient. On the other hand if you are comfortable configuring network devices doing so manually improves security.

3.2 Wired Ethernet

Modern digital networks are packet based. Ethernet “packets” are called frames. Data is divided into chunks called frames. Ethernet frames can be up to 1518 bytes long of which 1500 bytes are available for payload. 18 bytes are used for Ethernet addressing and frame management. When Gig Ethernet was developed the spec allowed larger frames, called Jumbo Frames but that need not concern us here. Each packet includes network specific information providing necessary information to deliver the packet. In the case of Ethernet this consists of sender and destination address, length of the packet, and error detection to verify errors did not corrupt the packet in transit.

3.2.1 10 – 100 – 1,000 – 10,000 – 100,000 Mbps

Initially UTP Ethernet operated at 10 million bits per second (10 Mbps) over Category 3 UTP wiring. Ethernet development has been in 10X increments. Fast Ethernet increased speed to 100 Mbps over Category 5 wiring. Gigabit Ethernet increased speed another 10 times to 1,000 Mbps. During Gigabit Ethernet development the Cat 5 specification was tightened resulting in Cat5e. The fastest version of Ethernet, 10 Gigabit (10,000 Mbps), has recently been modified to work over Cat 6a. Prior to that 10G required fiber. Work is under way on 100G. Given the high speed it is unlikely to operate over UTP, most likely some form of short distance coax.

3.2.2 Hubs vs Switches

Electrically UTP Ethernet is a point-to-point topology. Each Ethernet Interface must be connected to one and only one other Ethernet Interface. Hubs and Switches are used to regenerate Ethernet signals allowing devices to communicate with one another.

CDMA/CA scheme originally used by Ethernet places a limit on the number of wire segments and how many hubs can be used in a single collision domain. At 10 Mbps the 5-4-3 rule limits maximum to 5 wire segments with 4 hubs between devices, however only 3 of those hubs can have devices attached. For Fast Ethernet the rule is more stringent. A maximum of two Class II hubs, and the distance between hubs must be less than 5 meters. Class I hubs cannot connect directly to another hub. For all intents and purposes Fast Ethernet (100 Mbps) networks are limited to a single hub.

Ethernet switches work very differently then hubs. The Switch examines each arriving packet, reads the destination MAC address and passes it directly to the proper output port. Switches eliminate the collision domain allowing multiple conversations to occur simultaneously as opposed to being limited to only one with a hub. This dramatically increases network performance. A 100 Mbps hub shares 100 Mbps among all devices. A switch segments traffic betweens pairs of ports. A non-blocking 16-port 100 Mbps Ethernet switch has a maximum throughput of 1600 Mbps. This assumes 8 connections evenly divided between the 16 ports each one operating at full 100 Mbps. Port A is able to talk to port D at the same time Port F is talking to Port B. Switches enables full duplex communication. This means individual computers can be transmitting at the same time they are receiving. In actual use the speed improvement will be somewhat less but switches offer a tremendous performance advantage compared to hubs.

When a switch does not know which port to use it floods the incoming packet to all ports, much like a hub. When the device responds the switch learns the port and associates MAC address with that port. The switch also floods all ports with broadcast frames. Switches are transparent. Ethernet applications have no knowledge switches are being used instead of hubs. Switches used to be much more expensive then hubs. In recent years prices have come down dramatically making hubs obsolete while dramatically improving LAN performance.

Gig Ethernet NICs and Switches are almost at price parity with Fast Ethernet. Gig Ethernet LANs are an interesting inflection point. Historically computer performance has been limited by network speed. Gig Ethernet reverses that. When connected to Gig Ethernet typical PCs are only able to utilize a fraction of rated speed due to internal bottlenecks. Typical PC file transfer speed when used with Gig Ethernet is typically limited to 300-400 Mbps. The limitation is Disk speed, O/S overhead, and PCI throughput.

3.2.3 Managed vs Unmanaged Switches

Ethernet hubs and switches come in managed or unmanaged versions. Managed devices allow the administrator control of various parameters and observe traffic. Managed switches are overkill in a typical SOHO network. Unmanaged devices are considerably less expensive.

3.2.4 Automatic Link Configuration

To make Ethernet easier to use higher speeds are backward compatible. Transceivers Autonegotiate link characteristics to determine speed and whether connection is half or full duplex. Hubs are half duplex as only one device can be transmitting at a time. When connected to a switch a device is capable of transmitting and receiving at the same time – full duplex.

NIC (computer interface) is configured as uplink port (MDI), Hub or switch as MDI-X. 10 and 100 Mbps Ethernet use one pair for transmit and one for receive, Gig and 10 Gig use all four pair in each direction. Default configuration assumes MDI port is connected to MDI-X port. Having NICs wired as MDI and hub/switch as MDI-X means that in most cases interconnect is a simple 1:1 cable.

Problems occur when like devices are connected, say NIC to NIC or hub/switch to another hub/switch. To make this easier hubs/switches typically have an uplink switch or port. The uplink port reverses normal TX/RX configuration so another like device can be connected. The same effect can be obtained by using a crossover cable. Cross over cable swap TX and RX pair at one connector. Recently vendors have adopted Auto-MDIX to automatically determining remote port type and configure ports automatically. With Autonegotiation (Speed) and Auto-MDIX (gender) Ethernet has become more user friendly. All user need do is connect the cable everything else is automatic.

3.2.5 Topology

For maximum performance a single wide Ethernet switch should be used to serve the entire LAN. Cascading switches is transparent to traffic but limits inter switch speed to that of the link. With a single wide switch throughput is dictated by internal switch backbone performance.

3.2.6 Spanning Tree

Ethernet is designed such that one and only one path exist between any two endpoints. If multiple paths exist switches are unable to determine how to forward frames. Spanning Tree protocol was developed to address problem of multiple paths in complex networks. The protocol detects duplicate paths and turns off redundant paths. Spanning Tree requires managed Switches – low cost unmanaged switches do not implement the protocol. Spanning Tree is typically not an issue in simple SOHO LANs.

3.2.7 Power over Ethernet (PoE)

Until recently wired Ethernet delivered data but not power. Each device needed to provide its own power. For traditional “large” networked devices such as computers this was not a limitation. However as more and more low power Internet appliances such as WiFi Access Points and Voice over IP (VoIP) telephones were deployed benefit of delivering both data and power over the same cable became obvious.

IEEE took on the challenge and in 2005 released PoE specification. PoE provides 13 watts of power per device. The spec injects power two ways. For 10 and 100 Mbps Ethernet PoE uses the two unused pair. Gig uses all four pair so power has to be injected into the active pairs. IEEE 802.3at is currently working on a higher power version of PoE to increase power up to about 30 Watts.

PoE has been a boom for low powered devices. It also facilitates backup power, as UPS only needs to feed PoE Switch (or power injector) rather then every device.

3.3 Wireless Ethernet (WiFi)

Great strides have been made creating high performance low cost wireless LANs. RF technology is at its best where mobility is of paramount importance with bandwidth less so. WiFi radios operate in the unlicensed Industrial Scientific Medical (ISM) band. WiFi popularity has a down side. As more devices attempt to use limited frequency allocation interference problems increase. Government regulators are addressing interference by designating more bandwidth for unlicensed use. Standards bodies are working to facilitate peaceful coexistence between various devices.

IEEE 802.11 radios operate in two modes ad hoc peer-to-peer and managed. Managed mode requires an Access Point to bridge wireless network to wired network. Depending on size and type of construction a site may require multiple Access Points.

The success of various IEEE 802.11 Wireless standards has encouraged many vendors to enter the market. The WiFi Alliance works to insure interoperability between different vendors and promote use of Wireless LANs.

3.3.1 2 – 11 – 54 - 250 Mbps

Initial version of IEEE 802.11 delivered 2 Mbps in 2.4 GHz ISM band. 802.11b increased speed to 11 Mbps, 802.11g increased speed to 54 Mbps. 802.11a operates at 54 Mbps in the 5 GHz band. The much hyped 802.11n operates at 250 Mbps. Due to the way over-the-air transmission operates real world transfer speed is limited to about half raw transmission speed and often significantly lower.

3.3.2 Security

Wireless LANs are inherently less secure then wired. An intruder does not require a physical connection, but can eavesdrop while some distance away. The original 802.11 designers were aware of this risk and incorporated Wireless Equivalent Privacy (WEP) into the specification. Unfortunately almost immediately security researchers found critical weakness with WEP and shortly thereafter hacking tools became readily available making WEP virtually worthless. IEEE developed a comprehensive security standard and several enhanced implementations are available. The WiFi Alliance Security WiFi Protected Access (WPA) is current state of the art for wireless security. There are different versions optimized for residential and commercial customers. Netstumbler is a useful tool to help secure WiFi LANS.

3.3.3 Interference

WiFi radios operate in unlicensed bands so interference is a problem, especially in congested urban areas. Interference is the result of other WiFi radios, non WiFi radios operating in the same band such as Bluetooth and wireless phones and unintentional radiators such a microwave ovens.

The WiFi alliance has published numerous whitepapers on the subject. They are working with various standards bodies to make devices more aware of their RF environment by probing for other radios operating in the vicinity. Device use that knowledge to set operating channel and power to minimize mutual interference. Given the tremendous popularity of this technology governments are working to increase frequency allocation for unlicensed radio use. As radios get smarter and frequency allocation increase interference should become less of a problem.

3.4 Alternatives

Ethernet, wired and wireless, is the dominant LAN technology. The cost of installing network wiring is modest if done when structure is being built. The situation is more difficult for existing homes. The cost and disruption to retrofit a LAN is a significant deterrent. Various “no new wire” initiatives minimize impediments to home networking. These initiatives typically operate at lower speed than wired Ethernet but have the advantage of not requiring additional wiring.

It is a testament to Ethernet’s popularity these alternatives all use modified Ethernet frames, adapted to the physical medium, making it easy to bridge to standard Ethernet.

3.4.1 Phone Line Networking

Home Phoneline Network uses existing phone wiring to create bridged Ethernet LAN operating at a maximum speed of 320 Mbps. This allows computers to connect wherever a phone jack exists. The specification allows analog telephone, DSL, and LAN to coexist on a single pair of ordinary telephone wire.

Phone Line LAN uses slightly modified Ethernet packets. This makes HomePNA look like ordinary Ethernet to software. HomePNA equipped computers cannot connect to UTP Ethernet directly, a bridge is needed to rate match between the two networks and deal with minor signaling differences. This allows HomePNA and Ethernet devices to act as if they were connected to the same LAN.

3.4.2 Power line Networking

The HomePlug initiative provides high-speed network device that plug into ordinary AC receptacles at speeds up to 200 Mbps. The HomePlug Powerline Alliance is the clearinghouse for power line networking products.

3.4.3 Ethernet over TV Coax

An interesting new technology utilizes existing TV coax wiring to deliver Ethernet. Coaxsys and Multimedia over Coax Alliance are popularizing this technology. Many homes build in the last few decades have RJ6 coaxial cable feeding multiple TV outlets but are not equipped with Category rated cable suitable for conventional Ethernet. Verizon is using the technology to eliminate need to run both coax and UTP Ethernet when installing FIOS.

3.4.4 Ultra Wideband Radio

There are a number of emerging wireless technologies targeting so-called last-foot problem. One only has to look at the rear of typical residential TV/stereo/home theater installation to understand the problem. The mass of cabling needed to interconnect individual components and the inability of components to talk to one another hinders adoption and is at odds with ease of use. This limitation has dogged consumer electronics industry for years. The goal of Ultra Wideband and WirelessHD technology is to deliver incredibly fast data rates over a few meters eliminating need for interconnect cables.

4 Broadband Router – One Connection So Many Computers

When we first set up our network we used Wingate connections sharing software to share dialup. That was replaced with a MultiTech RF500S router used with Net-to-Net SDSL modem then later with a Westell B90 modem when we got Verizon ADSL. The main consideration was ability to fallback to dialup if DSL failed. At the time it was one of the few broadband routers that included automatic dialup fallback. This came in handy when our first broadband SDSL ISP went bankrupt. Verizon’s ADSL service has been very stable so several years ago we dropped dialup account.

Recently purchased a Netopia 3346N that combines ADSL2 modem, NAT router, Firewall, and 4-port Ethernet switch in a single device. This makes access to modem stats more convenient. Before we had to temporally connect DSL modem directly to PC, bypassing router, to access stats. Now stats are a web page accessible from any PC on the LAN.

The other reason for purchasing a router/modem combo was to experiment with newer modem that supports ADSL2 and ADSL2+. DSL market is evolving just like dialup market did. ITU has released several enhanced versions of ADSL that deliver higher speed and/or longer range. While Verizon is focused on rolling out Fiber to the Premise (FTTP) I assumed new generation DSLAM cards support ADSL2 and ADSL2+ whether Verizon chooses to market it or not. Had nothing to loose by using a newer modem, as it is backward compatible with previous generation of ADSL.

Using a router creates a clear distinction between LAN and WAN simplifying troubleshooting. The router market is extremely competitive. New routers can be had for less then $50 US and used higher end devices for similar price on eBay, which is where we purchased the Netopia router.

4.1 ADSL modem

The Netopia 3346N router has a built in ADSL and ADSL2+ compatible modem. Turns out our DSLAM only supports ADSL. Given low cost of the unit it was worth a try. Plus we are ready for ADSL2 if Verizon ever swaps out the DSLAM line card.

There are three main ways ADSL modems connect to ISP: Statically, DHCP, and PPPoE. Most business SDSL ISPs use static IP. With static customer manually enters IP setting into the router. Residential accounts typically use DHCP or PPPoE. DHCP works much the same as having a PC on the LAN. When modem powers up it searches for a DHCP server the server in turn automatically loads IP settings. Verizon uses Point-to-Point Protocol over Ethernet in our area. PPPoE works much the same as with dialup only much faster. PPPoE requires customer enter a user name and password.

Behind the scenes most Telcos use Asynchronous Transfer Mode (ATM) to transport IP packets. ATM normally requires configuring virtual circuit parameters. For Verizon VPI/VCI is 0/35 The Netopia modem automatically discovers these setting so all the customer needs to do is enter user name and password.

The modem maintains WAN connection even if it is unused for a long time making the connection instantaneously available.

We have 1500/384 ADSL residential package at about 14,000 feet from the Central Office. Once new router was set up throughput testing showed significantly higher speed. Prior to the upgrade download reported high 1300s low 1400s. After upgrade consistently reported slightly above 1500. Download speed remains the same near 384. Not sure if that was due to modem or router change but it was a nice surprise.

Being able to easily see DSL modem stats is a great diagnostic tool.

4.2 PPPoE and MTU

Point-to-Point Protocol over Ethernet (PPPoE) is an encapsulation protocol. PPPoE works much like dialup PPP to connect a computer over a point-to-point link to the ISP. With PPPoE speed is that of Ethernet rather then dialup modem.

Normally Ethernet packets are limited to 1500 bytes. This is also the typical maximum size transmitted over the Internet. PPPoE adds 8 bytes of overhead to each packet reducing maximum payload size to 1492. Internet protocols are designed to fragment and reassemble over large packets presented to it. However: many residential routers do not implement fragmentation. Even when properly implemented fragmentation incurs a significant performance penalty since an over large packet is split into two smaller ones with attendant IP overhead.

A better solution is to limit packet size so fragmentation/reassembly is not required. Windows TCP/IP stack implements path discovery this automatically limits packet size so fragmentation is not required. Typical Windows maximum transmission unit (MTU) size is 1452 bytes.

A good indication of overly large packet problem is if sending a little data <1500 bytes works but larger files do not.

4.3 Network Address Translation (NAT)

Most residential broadband ISPs restrict customer to a single IP address. The limited size of IPv4 address (32-bits) space means addresses are in short supply. ISPs often charge extra if more then one address is needed. This creates a quandary; how to cost effectively connect multiple hosts to the Internet? The most common solution is Network Address Translation (NAT) using private IP addresses. IETF RFC 1918 reserved three blocks of IP addresses guaranteed not used on the Internet. Because these addresses are not used on the public Internet they can be reused multiple times.

Combining NAT and private addresses allow an unlimited number of computers to share a single Internet connection and address. Network Address Translation (NAT) translates addresses on one side to addresses used on the other. NAT offers the advantage of a proxy server while being transparent to most applications. Proxy services were used extensively prior to deployment of NAT.

Internal LAN traffic proceeds normally; NAT is not required for local traffic. When a request cannot be serviced locally it is passed to NAT router, called a gateway. The router converts private address to the public address issued by the ISP and if needed modifies port number to support multiple sessions. The router sends modified packet to remote host as-if-it-originated-from-the-router. When reply is received router converts address and port number back to that of the originating device and forwards it to the LAN. The NAT router tracks individual sessions so multiple hosts are able to share a single address. As far as Internet hosts are concerned the entire LAN looks like a single computer.

4.3.1 Performance

NAT requires a lot of bookkeeping, changing IP and port addresses, then computing new packet checksum. Routers have no trouble keeping up with WAN connections of a few megabits per second. If you are blessed with really fast broadband connection say 5 or 10 or even 100 Mbps make sure router is up to the task.

Internal NAT translation tables limit the number of simultaneous sessions the router is able to maintain. This limit does not affect normal Internet usage. However when Peer-to-Peer (P2P) is used the very large number of sessions may overwhelm a low-end router.

4.3.2 Security

NAT blocks remotely originated traffic. It functions as a de facto firewall because router does not know where to forward packets that originate outside the LAN unless specifically programmed to do so.

4.3.3 Limitations of NAT

As useful as NAT is it is also controversial. It breaks the end-to-end Internet addressing paradigm. NAT maintains state information. If it fails session recovery is not possible. It interferes with server functionality and IPsec VPNs.

When NAT was first developed it was assumed private address pool was truly private and no one but the local administrator cared about local address usage. Today in the age of VPNs these internal addresses ARE being exposed to other networks. If a telecommuter’s residential LAN and office network both use private addresses they may overlap. In a simple case this is not major problem, the user simply moves the LAN to a different address block. But what happens if home LAN must support multiple telecommuters? This requires coordination of multiple corporate LANs and SOHO LAN. In this case it may be impossible to resolve address collisions if multiple networks use identical address blocks.

This is not to discourage use of NAT it is very powerful technique. But NAT should be seen for what it is, a short-term workaround to minimize effects of IPv4 address shortage, not a permanent extension to Internet technology. For more information see RFC 2993 Architectural Implications of NAT.

4.4 LAN IP Address Assignment

Each device on the network requires a unique IP address. These addresses are not used on the Internet therefore they are not coordinated by IANA. However they must be coordinated within the LAN. The router has the flexibility to use static, dynamic address allocation.

4.4.1 Static

When static allocation is used IP parameters: address, subnet mask, gateway address, and DNS address need be manually assigned to the computer. The router’s DHCP server issues addresses in 192.168.2.2 - 192.168.2.100 range with a subnet mask of 255.255.255.0. Static addresses can be assigned in the range 192.168.2.101 – 192.168.2.254. This keeps all addresses in the same subnet without interfering with DHCP operation.

4.4.2 Dynamic

This is the default Windows IP configuration, at power up PC searches for a DHCP server. The DHCP server in the router assigns each machine’s IP parameters. Once PC is configured it is able to communicate. The address is “leased” to the client. Prior to lease expiration client attempts to renew it. Under normal conditions the lease never expires and client IP address remains the same. If client is off network for extended period of time lease will expire. Next time computer is attached will likely receive different IP address.

4.4.3 MAC Reservation

For some devices, such as servers, dynamic addresses are inconvenient. For example binding to HP printer is by IP address, as it does not have a name. If server’s address changes each client has to be reconfigured. A solution is to create a pseudo static address. The address issued by the DHCP server is bound to the client’s Ethernet MAC address. As long as MAC address does not change device is always assigned the same IP address. This is more convenient than setting static addresses manually on each device.

All machines, except guests, are issued pseudo static addresses. This makes it much easier to interpret SysLog entries that record events based on IP address.

Status of PCs and whether or not they are active.

4.5 10/100 Ethernet Switch

The office is wired with 4 Ethernet drops fed by a 16-port 10/100 Ethernet Switch. This turned out to be inadequate so the Router’s 4-port Ethernet switch comes in handy. One port feeds the 16-port Ethernet switch. The file server and office desktop connect to the switch everything else goes through the whole house switch. This increased number of office ports to 6 eliminating need to pull more wire.

Most modern Ethernet switches include Auto-MDX. The switch checks link configuration and automatically selects the correct port type depending if switch is connected to a PC or another switch. This eliminates hassle of using crossover cable or up-link ports to interconnect multiple switches.

4.6 DNS

Host name resolution for local devices is performed by NetBIOS over IP. If Windows cannot resolve a host name it assumes it is a remote host and forwards the request to the router’s IP address. The router then forwards request to Verizon DNS nameserver. To devices on the LAN the router looks like a DNS server.

We run a local DNS nameserver that requires overriding the settings provided by Verizon. Unfortunately the router does not include a mechanism to point to an internal nameserver. The workaround is to manually configure DNS nameserver address in each client’s TCP/IP configuration. The primary DNS address is the internal DNS server, secondary points to router in case local server is down.

4.7 Gateway

Each PC forwards packets that cannot be delivered locally to the gateway. The gateway router decides how to deliver packets that travel outside the LAN. Only a single connection exists between our network and the ISP so routing is trivial. The router simply forwards all packets to the gateway address assigned by the ISP.

4.8 Firewall

The router includes a stateful inspection firewall. This provides another layer of security by observing inbound and outbound traffic and dropping nonconforming packets.

4.9 QoS

Ethernet and the Internet were designed as egalitarian best effort services. As packets arrive at switch or router they are accepted on a first come first serve basis and either delivered to proper destination or forwarded them to next router. As long as communication paths are fast compared to offered load best effort works well. Packets arrive; they are queued for a short time then sent on their way. The difficulty occurs when packets arrive faster then they can be handled. The Internet has various mechanisms to slowdown packet inflow when nodes become congested. The sender is requested to slow down and in extreme circumstances packets are discarded.

Quality of Service (QoS) mechanisms place different values (Diffserv) on packets so when congestion occurs higher value packets are delivered as quickly as possible. Lower value packets are delayed during minor congestion or discarded during extreme congestion.

As the Internet increasing carries data with varying latency requirements efforts are under way to mark packets with a latency metric. In the event of congestion high value packets are bumped to the head of the line. For example during a Voice over IP (VoIP) phone call round trip latency should be under 150ms. Excessive delay makes carrying on a normal voice conversation difficult and with extreme delay virtually impossible. On the other hand if a print job’s packet is delayed even a second other then delaying printout a little no one is likely to even notice.

Residential broadband customers are especially vulnerable to latency issues as a result of asymmetric service. Most residential service had upload as a small fraction of download. This disparity makes it easy to saturated upload path. For example TCP/IP, the protocol used for file transfer, constantly transmits acknowledgements (ACKs) back to the sender letting it know data is arriving correctly. If ACKs are delayed sender will stop sending waiting for the receiver to “catch up” or in extreme cases resend data assuming it was lost.

QoS services allow more graceful congestion degradation by moving high priority packets to the head of the queue. QoS is not a panacea, it does not create more capacity, it simply changes winners and losers.

4.10 Syslog Event Logging

The router logs significant events and forwards them to the Syslog server. This overcomes one of the main limitations using a dedicated device for Internet sharing – limited data storage space. The router emits SysLog data to the PC server. One of the services running on the server is Kiwi SysLog. The SysLog server stores data from both the Router and Tardis Time server for later review.

4.11 Public Server Behind NAT

Running a public server behind NAT requires router to forward incoming connection requests to the appropriate server. By default incoming connection requests are discarded because router does not know which host on the LAN to forward them. The router acts as an inbound firewall. Port forwarding configures the router to accept an inbound connection request, to say port 80, and forward to the web server. To the remote host the server looks like it is using the public IP address, when in fact it is on a private address block.

4.11.1 Local Loopback

Most Residential NAT routers do not perform WAN loopback. This prevents access to local public server by its domain name or public IP address from within the LAN. The server must be accessed by its LAN machine name or LAN IP address. When the server is accessed by public IP address the router forwards the request to the Internet. It does not realize the host is local. The packet never reaches the server.

If local access by DNS name or public address is important add the name/address information to Windows Host file. The Host file performs static name translation service invoked prior to DNS. If the requested host name is found in Hosts file Windows will use that address and not query DNS.

4.11.2 Active vs Passive FTP

The way File Transfer Protocol (FTP) allocates ports causes problems with NAT. To NAT the connection appears to originate from the server, rather then user. This causes NAT to prevent the transfer. This can be a problem if your change FTP ports from default 20/21 to some other value. NAT routers only know how to handle FTP on the default port.

To learn more read: Active FTP vs. Passive FTP, a Definitive Explanation.

4.11.3 Multiple Identical Servers

Most residential broadband ISPs only allocate a single IP address per customer. This causes problems running multiple servers of the same type. For example when running a web server, all incoming requests to port 80 are redirected to that server, this makes it impossible to run two web servers on a single IP address using the well-known port. The work around is to use a different port for one of the web servers. This can cause problems since the remote user has no way to know the server is using a non standard port. Many DynamicDNS sites have provisions to redirect the request to the alternate port.

4.11.4 Dynamic DNS

In order for a remote user to access a server it needs to know the host name to be able to look ups its IP address. DNS assumes server configuration is static and changes only rarely and then changes are made the system administrator.

This poses a problem for residential customers with dynamic address allocation since server address may change suddenly without notice. Several services have sprung up to address this issue. Dynamic DNS services either run a small application on the router or on the server to detect when public IP address changes. When that happens the Dynamic DNS service database is notified of new address. This is not a perfect solution since there can be significant delay between address changes and when new address is available. However for most casual residential users it works well.

4.11.5 Security

Great care should be taken when running public servers. If an attacker is able to exploit a weakness in the server they gain access to the entire LAN. Once in control of a compromised serve they are free to attempt to attack other machines on the LAN. We use a hosting service to minimize security risk rather then run public server locally.

5 Local Server – Just Like the Big Kids

The server provides several network services: file sharing, DNS nameserver, NIST clock synchronization, Syslog log server, private web server and local weather station. At first we used a laptop as the server. This was convenient because it was self-contained but had limited disk storage capacity. It was replaced with a recycled 200Mz Pentium desktop with a 45GB hard drive. Most recently the server has been replaced with a 1 GHz Pentium with 320 Gig drive running XP.

5.1 KVM Switch

We did not want to add another set of user I/O when we setup the desktop server. The solution was to use a KVM (keyboard, video, mouse) switch. KVM’s have been used in server farms for years to allow single point of control for multiple computers. We purchased a 4 port Belkin Omni View SE KVM. Port 1 is the workstation port 2 the server leaving 2 ports for future use.

Switching between computers is done via a button on the KVM or a keyboard hot-key sequence. The KVM creates virtual devices for each computer. When switching computers the KVM reconnects keyboard, mouse and monitor to the active computer and programs real devices to match stored virtual device configuration.

Video Performance Tip -- Workstations use higher video resolution and faster refresh rate than servers resulting in very high video data rate. This is typically not a problem for the KVM itself but requires high quality cable. The video cable should use coax for the three video signals. Coax preserves high frequency and minimizes crosstalk between video signals.

Mouse Compatibility Tip -- Each computer thinks it is directly connected to a keyboard, mouse and monitor. The KVM must memorize commands sent to each device and reconfigure the device each time user selects a different computer. Mice cause problems because so many proprietary enhancements exist. For compatibility PS/2 mice power up in compatibility mode this allows mouse functionally even if mouse specific driver is not installed. At power up mouse device driver performs a “knock” sequence to determine if a known mouse is attached. If the mouse answers correctly the dri