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The Cisco IOS software supports a variety of routing protocols. The Network Protocols Configuration Guide, Part 1 discusses the following network protocols:
The Network Protocols Configuration Guide, Part 2 discusses the following network protocols:
This overview chapter gives a high-level description of AppleTalk, IP, and Novell IPX. For configuration information, refer to the appropriate chapter in this publication.
AppleTalk is a LAN system designed and developed by Apple Computer, Inc. It can run over Ethernet, Token Ring, and Fiber Data Distributed Interface (FDDI) networks, and over Apple's proprietary twisted-pair media access system (LocalTalk). AppleTalk specifies a protocol stack comprising several protocols that direct the flow of traffic over the network.
Apple Computer uses the name AppleTalk to refer to the Apple network protocol architecture. Apple Computer refers to the actual transmission media used in an AppleTalk network as LocalTalk, TokenTalk (AppleTalk over Token Ring), EtherTalk (AppleTalk over Ethernet), and FDDITalk (AppleTalk over FDDI).
Cisco IOS software supports AppleTalk Phase 1 and AppleTalk Phase 2. For AppleTalk Phase 2, Cisco devices support both extended and nonextended networks. Cisco's implementation of AppleTalk routes packets over Ethernet, Token Ring, and FDDI LANs, and over X.25, High-Level Data Link Control (HDLC), Frame Relay, and Switched Multimegabit Data Service (SMDS) WANs.
Cisco routers and access servers also support AppleTalk Enhanced IGRP. AppleTalk Enhanced IGRP provides the following features:
The Cisco implementation of AppleTalk supports the following standard AppleTalk protocols:
AARP, DDP, and RTMP provide end-to-end connectivity between internetworked nodes. AARP maps AppleTalk node addresses to the addresses of the underlying data link, thus making it possible for AppleTalk to run on several data links. DDP provides socket-to-socket delivery of packets. RTMP establishes and maintains routing tables.
NBP and ZIP maintain node name and zone information. NBP maps network names to AppleTalk addresses. ZIP tracks which networks are in which zones.
AEP is an echo, or ping-type, protocol. It generates packets that test the reachability of network nodes.
ATP is a reliable transport protocol that provides data acknowledgment and retransmission for transaction-based applications, such as file services provided by the AppleTalk Filing Protocol (AFP) and print services provided by the Printer Access Protocol (PAP).
Our software provides support for the AppleTalk Management Information Base (MIB) variables as described in RFC 1243.
The Cisco AppleTalk implementation includes the following enhancements to standard AppleTalk:
AppleTalk, like many network protocols, makes no provisions for network security. The design of the AppleTalk protocol architecture requires that security measures be implemented at higher application levels. Cisco supports AppleTalk distribution lists, allowing control of routing updates on a per-interface basis. This security feature is similar to those that Cisco provides for other protocols.
Note that Cisco's implementation of AppleTalk does not forward packets with local source and destination network addresses. This behavior does not conform with the definition of AppleTalk in Apple Computer's Inside AppleTalk publication. However, this behavior is designed to prevent any possible corruption of the AARP table in any AppleTalk node that is performing Media Access Control (MAC)-address gleaning.
A Cisco router or access server may receive equivalent routes advertised by neighboring routers with one router giving an AppleTalk Phase 1 form of the route, for example, 101, and another giving an AppleTalk Phase 2 form of the route, for example, 101-101. When neighboring routers advertise equivalent overlapping routes to a router, the router always uses the AppleTalk Phase 2 form of the route and discards the AppleTalk Phase 1 route.
The Internet Protocol (IP) is a packet-based protocol used to exchange data over computer networks. IP handles addressing, fragmentation, reassembly, and protocol demultiplexing. It is the foundation on which all other IP protocols, collectively referred to as the IP Protocol suite, are built. IP is a network-layer protocol that contains addressing and control information that allows data packets to be routed.
The Transmission Control Protocol (TCP) is built upon the IP layer. TCP is a connection-oriented protocol that specifies the format of data and acknowledgments used in the transfer of data. TCP also specifies the procedures that the computers use to ensure that the data arrives correctly. TCP allows multiple applications on a system to communicate concurrently because it handles all demultiplexing of the incoming traffic among the application programs.
Cisco's implementation of IP provides most of the major services contained in the various protocol specifications. Cisco IOS software also provides the TCP and User Datagram Protocol (UDP) services called Echo and Discard, which are described in RFCs 862 and 863, respectively.
Cisco supports both TCP and UDP at the transport layer, for maximum flexibility in services. Cisco also supports all standards for IP broadcasts.
Cisco's implementation of each of the IP routing protocols is discussed in detail at the beginning of the individual protocol sections throughout the IP Routing chapter in this publication.
IP routing protocols are divided into two classes: Interior Gateway Protocols (IGPs) and Exterior Gateway Protocols (EGPs). The IGPs and EGPs that Cisco supports are listed in the following sections.
Interior protocols are used for routing networks that are under a common network administration. All IP interior gateway protocols must be specified with a list of associated networks before routing activities can begin. A routing process listens to updates from other routers on these networks and broadcasts its own routing information on those same networks. Cisco IOS software supports the interior routing protocols:
Exterior protocols are used to exchange routing information between networks that do not share a common administration. IP exterior gateway protocols require three sets of information before routing can begin:
The supported exterior gateway protocols are:
Our routers and access servers also support two router discovery protocols, Gateway Discovery Protocol (GDP) and Internet Control Message Protocol (ICMP) Router Discovery Protocol (IRDP), which allow hosts to locate routers and access servers.
GDP was developed by Cisco and is not an industry standard. Unsupported example GDP clients can be obtained upon request from Cisco. Our IRDP implementation fully conforms to the router discovery protocol outlined in RFC 1256.
You can configure multiple routing protocols in a single router or access server to connect networks that use different routing protocols. You can, for example, run RIP on one subnetted network, IGRP on another subnetted network, and exchange routing information between them in a controlled fashion. The available routing protocols were not designed to interoperate, so each protocol collects different types of information and reacts to topology changes in its own way. For example, RIP uses a hop-count metric and IGRP uses a five-element vector of metric information. In the case where routing information is being exchanged between different networks that use different routing protocols, there are many configuration options that allow you to filter the exchange of routing information.
The Cisco IOS software can handle simultaneous operation of up to 30 dynamic IP routing processes. The combination of routing processes on a router or access server consists of the following protocols (with the limits noted):
Novell Internet Packet Exchange (IPX) is derived from the Xerox Network Systems (XNS) Internet Datagram Protocol (IDP). IPX and XNS have the following differences:
Cisco's implementation of Novell's IPX protocol is certified to provide full IPX routing functionality.
Cisco supports the IPX MIB (currently, read-only access is supported). The IPX Accounting group represents one of the local Cisco-specific IPX variables we support. This group provides access to the active database that is created and maintained if IPX accounting is enabled on a router or access server.
Cisco IOS software also supports IPX Enhanced IGRP, which provides the following features:
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