Networking Protocols Networking

In the following sections, you will learn about four major protocol stacks and how each one handles the concepts of addressing, routing, interoperability, and naming:

  • TCP/IP
  • IPX/SPX
  • NetBEUI
  • AppleTalk/AppleTalk over IP

TCP/IP
Transmission Control Protocol/Internet Protocol (TCP/IP) is the protocol suite of choice today. It, like other protocols suites, is used to allow local network devices to communicate over a network. However, TCP/IP is used not only on LANs, but also over WANs and the Internet. Actually, TCP/IP is the only protocol suite in use on the Internet.

Addressing
Each host is given (either manually or automatically) a dotted decimal IP address in the format xxx.xxx.xxx.xxx, where xxx is a number from 0 to 255.

Because addressing is a Network layer concept, the protocols that deal with addressing can be found at this layer. The Address Resolution Protocol (ARP) is responsible for resolving an IP address to the MAC address of the receiving host. The MAC address is a Data Link layer address hard-coded to each network interface by the manufacturer. When a TCP/IP packet is sent, at some point a router will need to determine exactly which device the packet is intended for. On Ethernet networks, the router will use an ARP request broadcast. Any device that wants a specific physical address will send an ARP broadcast on to the immediate link with the IP address of the interface for which it wants the MAC address in the packet header. The device whose interface has the matching IP address will respond with its interface’s MAC address. Whenever a device sends an ARP request and receives a response, it notes that resolution in a table known as the ARP cache. When a router receives packets and needs to send them to a particular device on one of its own segments, it examines the IP address of the destination, looks up the MAC address of that device’s interface using ARP, and forwards the packet via Ethernet to the intended destination.

Routing
On TCP/IP networks, routing is a fairly involved process. In order to send a packet through an internetwork (like the Internet), the router must have three pieces of information:

  • The IP address of the sender
  • The IP address of the destination
  • The IP address of the next router to which the packet should be sent

The first two are part of the IP datagram being sent, but the router must figure out the last item itself. The router uses information it receives from other routers about what IP networks their interfaces are members of, as well as other networks they have learned about from their neighbors, in order to build a logical “map” of the network (called a routing table). Then the router can determine the best way to get the datagram to its destination and send the information on to the next router.

Routers build routing tables using dynamic routing protocols, such as RIP and Open Shortest Path First (OSPF), or by having static routes entered manually. The major difference between the two dynamic routing protocols mentioned is that RIP is a distance vector routing protocol and OSPF is a link state routing protocol. The difference between them is pretty simple. Distance vector protocols (like RIP) are used by routers to gather information about the hosts connected to them and to build a table of the addresses and the segment they are on (called a routing table). The router then sends out this information to all the routers it is connected to. All of the routers that receive this information add the route information to their own routing tables and continute to propagate them. Approximately every 30 seconds (varies depending on the protocol), distance vector protocol routers will re-advertise their entire routing table, with each interface having its own independent timer. Eventually, all routers in the internetwork know about all the other routers and the networks they serve.

,p>Link state routing protocols(like OSPF) work slightly differently. Whereas IP RIP routers will advertise their entire routing table every 30 seconds, a link state router will send out to its “neighbors” only the changes to its routing table, as they occur. Additionally, link state routers have a more directed relationship with their neighbors. Instead of blindly advertising all of their information to their neighbors, link state protocols (like OSPF) prefer to more intentionally send updates only to a specific list of addresses via unicast or multicast.

Interoperability
Of all the protocols listed in this chapter, no protocol is more flexible or more interoperable than TCP/IP. As the Internet gained popularity, everyone wanted to “get on the Net.” As such, almost every computer had to have two things: a web browser and some form of TCP/IP connection. Therefore, every computer that is connected to the Internet is running TCP/IP in one way or another. Many companies use the TCP/IP protocol suite to communicate with one another over the Internet.

Additionally, because of this phenomenon, every operating system has some form of TCP/IP protocol stack and, as such, can communicate with other operating systems on some fundamental level.

Naming
TCP/IP hosts are named according to the DNS convention. DNS is a service that resolves FQDNs to IP addresses. For instance, you can use friendly names like www.trainsolutions.com to refer to computers instead of unfriendly IP addresses like 192.168.24.31.

There are two parts to a DNS name: the host name (e.g., www) and the domain name (e.g., trainsolutions.com). Each of these components is separated by a period. Typically, you would assign a host name that says what the computer’s function is (e.g., www for a web server). The domain name, on the other hand, is usually the name of the company in which the computer resides, or some related name, followed by .com, .edu, .net, or any other top-level domain suffix.

IPX/SPX
When Novell NetWare was introduced, it was designed to be a server platform for a local area and wide area networks. To that end, Novell designed a protocol stack that was very efficient over local area networks and that would also work on wide area networks. That protocol stack was the Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX).

In the following sections similar information to that presented for TCP/IP will be presented so that you may compare similar features, including addressing, routing, and naming, between the two.

Addressing

IPX is the Network layer protocol that handles addressing and routing for the IPX/SPX protocol stack. IPX addressing is actually very simple. It takes the 12-digit hexadecimal address because that is the address for the individual node on that network segment. The network segment is referred to by its own unique 8-digit hexadecimal address. For example, the address 0001ABF3:12AB341FF414 would correspond to an interface with a MAC address of 12-AB- 34-1F-F4-14 on the network segment labeled 0001ABF3. Every network segment is assigned its own, unique IPX network address. Since the MAC address is burned in to the NIC at the factory and, for the most part, shouldn’t be changed, it doesn’t have to be configured. The only configuration that must be done is to assign the IPX network address and configure the server with that address.

Routing

Most routers that route TCP/IP traffic can also route IPX traffic (although they may require additional software or configuration). IPX/SPX is a routable protocol stack because its address strucure is hierarchical, with a network portion and a node portion. As a result and to increase functionality, IPX/SPX has routing protocols designed into it. The routing protocols for IPX/ SPX are RIP and NLSP.

IPX RIP is very similar to the RIP protocol in TCP/IP in that it is the distance vector routing protocol for IPX. Similarly, NLSP is the link state routing protocol for IPX/SPX. Both work similarly to their TCP/IP counterparts. RIP uses broadcasts of the entire IPX routing tables to keep all IPX routers updated, although every 60 seconds, not 30 as with IP RIP, and just as OSPF does, NLSP sends out only the changes to the routing tables and then only to a select group of network addresses. NLSP is actually based on another link state routing protocol, ISO’s Intermediate Sytem to Intermediate System (IS-IS).

Interoperability

IPX/SPX isn’t as ubiquitous as TCP/IP (which can even be found running on Coke machines), but it holds its own when it comes to allowing many different platforms to talk. Windows 9x, NT, Me, 2000, XP, and2003 as well as NetWare, and a few versions of Linux come “out of the box” with support for communicating with other entities via the IPX/SPX protocol stack, although Microsoft calls its completely compatible version NWLink. Before the popularity explosion of the Internet in the mid-1990s, the IPX/SPX protocol stack was the only protocol stack many companies would run.

The only downside to interoperability using IPX/SPX is that many versions of Unix and other high-end operating systems like OS/400 don’t come with built-in support for the IPX/SPX protocol stack or even with an option for support.

Naming
Really, the only devices that have names are the NetWare servers. Generally speaking, you can name a NetWare server anything you want, as long as you follow these rules:

  • name must not include any of the “illegal” characters, including a period (.), a comma (,), a plus sign (+), an equal sign (=), and a backslash ().
  • Names must have fewer than 64 characters.
  • Names are not case sensitive.

These names are resolved using either Bindery Services or Novell Directory Services.

AppleTalk and AppleTalk over IP

When Apple introduced the Macintosh in 1984, the Mac included networking software. This networking software used a protocol known as AppleTalk and a cabling system known as LocalTalk. It is a very simple and elegant protocol in that the computer takes care of most of the configuration. You simply plug it in and it works. Because of its simplicity and popularity with Mac users, and because the Mac users wanted a faster version, Apple developed Apple- Talk version 2 with support for Ethernet (EtherTalk).

Apple’s Mac OS X and OS X Panther (versions 10.3.x) can communicate with any server running the AFP service, whether over TCP/IP, which is preferred by Apple, or over the legacy Apple- Talk protocol. On Macintosh servers, the AFP service is implemented as AppleShare. You can use IP to connect to Macintosh file services running on Mac OS X Server, AppleShare IP, and Windows 2000 and later servers. AppleShare IP has been an add-on service available since the Mac OS 8 days, necessary for IP connectivity with AFP resources before this functionality became available natively in Mac OS X. Of course, Mac OS X still is capable of communicating with AFP servers over AppleTalk instead of IP, supporting legacy access to older AppleShare servers and Windows NT servers that only provide Mac file services over AppleTalk. However, Apple recommends migrating to TCP/IP as the transport method between clients and AFP servers.

Services for Macintosh
Although the Windows 2000 file system is fairly different from the Macintosh file system, files on a Windows 2000 Server machine are accessible by both Windows 2000 clients and Macintosh clients. Services for Macintosh works in the background on a Windows 2000 Server machine to make this multiclient support possible by establishing an AFP-compatible server service. Files can be made to appear as they usually do for both Macintosh and Microsoft clients. A Microsoft client sees files represented as a directory tree, while a Macintosh client sees files represented as a Macintosh folder. In this environment, files may be stored in shared folders or Macintosh volumes. Macintosh volumes that are shared to the network are seen only by Macintosh clients, not by the Windows 2000 clients. Conversely, in order for a Macintosh client to gain access to a Microsoft shared folder, the administrator must designate the folder as a Macintosh-accessible volume.

For folders that are both a Microsoft shared folder and a Macintosh-accessible volume, both Microsoft clients and Macintosh clients have access to the resource. However, while Microsoft clients see folders and files as they are stored on the server’s hard disk beneath the root of the share, Macintosh clients see the volume as containing Macintosh files and folders.

Addressing
Each station on an AppleTalk network uses an address that is 24 bits long. Sixteen of those bits are given to the network, and each network can support 254 nodes. Each network segment can be given either a single 16-bit network number or a range of 16-bit network numbers. If a network is assigned a range of numbers, that network is considered an Extended AppleTalk network because it can support more than 254 nodes. The node address is automatically assigned by the computer itself.

In addition to network numbers, AppleTalk networks use areas called zones. Zones allow an administrator to divide a network into logical areas for easier administration and to make it easier for a user to find resources.

Routing

AppleTalk wasn’t originally designed to be routed over a WAN, but with the release of AppleTalk version 2, Apple included routing functionality with the introduction of the Routing Table Maintenance Protocol (RTMP). RTMP is a distance vector routing protocol, like RIP, for both IP and IPX.

Interoperability
The only computer that comes with AppleTalk installed by default is the Macintosh. Most Windows operating systems are able to use the AppleTalk protocol but require that additional software be installed. By using AppleTalk over IP, it is possible to tunnel AppleTalk conversations over the very Internet itself. Two AppleTalk speakers can package their AppleTalk packets in such a way that they are transmissible through IP intermediate systems, being stripped back down to the original AppleTalk packet by the receiving AppleTalk-speaking device.

Naming
AppleTalk uses the Name Binding Protocol (NBP) to associate the name of the computer with its network address. It is broadcast based. Every station broadcasts its name when it comes up on a network.

The AppleTalk router on a network will cache these names and respond when a node requests a name resolution; the local router will answer with information it has obtained from this NBP cache.

AppleTalk and AppleTalk over IP

When Apple introduced the Macintosh in 1984, the Mac included networking software. This networking software used a protocol known as AppleTalk and a cabling system known as LocalTalk. It is a very simple and elegant protocol in that the computer takes care of most of the configuration. You simply plug it in and it works. Because of its simplicity and popularity with Mac users, and because the Mac users wanted a faster version, Apple developed Apple- Talk version 2 with support for Ethernet (EtherTalk).

The Apple Talk Protocol Model

Apple Talk Protocol Model

Apple Talk Protocol Defined

Apple Talk Protocol Defined

Apple’s Mac OS X and OS X Panther (versions 10.3.x) can communicate with any server running the AFP service, whether over TCP/IP, which is preferred by Apple, or over the legacy Apple- Talk protocol. On Macintosh servers, the AFP service is implemented as AppleShare. You can use IP to connect to Macintosh file services running on Mac OS X Server, AppleShare IP, and Windows 2000 and later servers. AppleShare IP has been an add-on service available since the Mac OS 8 days, necessary for IP connectivity with AFP resources before this functionality became available natively in Mac OS X. Of course, Mac OS X still is capable of communicating with AFP servers over AppleTalk instead of IP, supporting legacy access to older AppleShare servers and Windows NT servers that only provide Mac file services over AppleTalk. However, Apple recommends migrating to TCP/IP as the transport method between clients and AFP servers.

Services for Macintosh
Although the Windows 2000 file system is fairly different from the Macintosh file system, files on a Windows 2000 Server machine are accessible by both Windows 2000 clients and Macintosh clients. Services for Macintosh works in the background on a Windows 2000 Server machine to make this multiclient support possible by establishing an AFP-compatible server service. Files can be made to appear as they usually do for both Macintosh and Microsoft clients. A Microsoft client sees files represented as a directory tree, while a Macintosh client sees files represented as a Macintosh folder. In this environment, files may be stored in shared folders or Macintosh volumes. Macintosh volumes that are shared to the network are seen only by Macintosh clients, not by the Windows 2000 clients. Conversely, in order for a Macintosh client to gain access to a Microsoft shared folder, the administrator must designate the folder as a Macintosh-accessible volume.

For folders that are both a Microsoft shared folder and a Macintosh-accessible volume, both Microsoft clients and Macintosh clients have access to the resource. However, while Microsoft clients see folders and files as they are stored on the server’s hard disk beneath the root of the share, Macintosh clients see the volume as containing Macintosh files and folders.

Addressing
Each station on an AppleTalk network uses an address that is 24 bits long. Sixteen of those bits are given to the network, and each network can support 254 nodes. Each network segment can be given either a single 16-bit network number or a range of 16-bit network numbers. If a network is assigned a range of numbers, that network is considered an Extended AppleTalk network because it can support more than 254 nodes. The node address is automatically assigned by the computer itself.

In addition to network numbers, AppleTalk networks use areas called zones. Zones allow an administrator to divide a network into logical areas for easier administration and to make it easier for a user to find resources.

Routing

AppleTalk wasn’t originally designed to be routed over a WAN, but with the release of AppleTalk version 2, Apple included routing functionality with the introduction of the Routing Table Maintenance Protocol (RTMP). RTMP is a distance vector routing protocol, like RIP, for both IP and IPX.

Interoperability
The only computer that comes with AppleTalk installed by default is the Macintosh. Most Windows operating systems are able to use the AppleTalk protocol but require that additional software be installed. By using AppleTalk over IP, it is possible to tunnel AppleTalk conversations over the very Internet itself. Two AppleTalk speakers can package their AppleTalk packets in such a way that they are transmissible through IP intermediate systems, being stripped back down to the original AppleTalk packet by the receiving AppleTalk-speaking device.

Naming
AppleTalk uses the Name Binding Protocol (NBP) to associate the name of the computer with its network address. It is broadcast based. Every station broadcasts its name when it comes up on a network.

The AppleTalk router on a network will cache these names and respond when a node requests a name resolution; the local router will answer with information it has obtained from this NBP cache.



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