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Network Protocols Overview

Network Protocols Overview

The Cisco IOS software supports a variety of network protocols, from popular protocols such as Internet Protocol (IP) and AppleTalk to less frequently used protocols such as Apollo Domain and XNS.

The Network Protocols Configuration Guide, Part 3 and Network Protocols Command Reference, Part 3 discuss the following network protocols:

This overview chapter provides a high-level description of each technology. For configuration information, refer to the appropriate chapter in this module.

Parts 1 and 2 of the Network Protocols Configuration Guide and Network Protocols Command Reference provide information about the following additional protocols:

Note Not all Cisco access servers support the protocols described in this publication. For a model-by-model list of supported protocols, refer to the Release Notes for Cisco IOS Release 11.2.

Apollo Domain

The Cisco IOS software implementation supports packet forwarding and routing for the Apollo Domain network protocols on Ethernet, Fiber Distributed Data Interface (FDDI), and serial interfaces using High-Level Data Link Control (HDLC) or X.25 encapsulation. The software implementation does not support direct attachment to the 12-MB Domain Token Ring. The following restrictions apply to the Cisco implementation of Apollo Domain:

Note Release10.0 of the Apollo Domain operating system does not provide ARP. You must migrate to Release10.1 and later versions before you can operate with Cisco routers. Cisco routers support neither the rtchk and lcnode commands nor Domain ARP in
Apollo's 802.5 implementation.

Banyan VINES

The Banyan Virtual Network Service (VINES) protocol is a networking system for personal computers. This proprietary protocol was developed by Banyan Systems, Inc., and is derived from the Xerox Network System (XNS) protocol. Cisco's implementation of VINES has been designed in conjunction with Banyan.

Cisco's implementation of Banyan VINES provides routing of VINES packets on all media. Although the software automatically determines a metric value that it uses for routing updates based on the delay set for the interface, this software implementation allows you to customize the metric. Cisco's implementation also offers address resolution to respond to address requests and broadcast address propagation. Echo support at the Media Access Control (MAC) level is also available for Ethernet, IEEE 802.2, Token Ring, and FDDI media. Name-to-address mapping for VINES host names also is supported, as are access lists to filter packets to or from a specific network.


Digital Equipment Corporation designed the DECnet stack of protocols in the 1970s as part of its Digital Network Architecture (DNA). DNA supports DECnet routing over Ethernet, Token Ring, FDDI, HDLC, Point-to-Point Protocol (PPP), Frame Relay, Switched Multimegabit Data Service (SMDS), X.25, and IEEE 802.2.

DECnet supports both connectionless and connection-oriented network layers implemented by Open System Interconnection (OSI) protocols. DECnet's most recent product release is called Phase V, which is equivalent to International Organization for Standardization (ISO) Connectionless Network Service (CLNS). Phase V is compatible with the previous release, Phase IV. Phase IV was similar to OSI routing, but Phase V implements full OSI routing, including support for End System-to-Intermediate System (ES-IS) and Intermediate System-to-Intermediate System (IS-IS) connections. An end system (ES) is a nonrouting network node; an intermediate system (IS) refers to a router. ES-IS support allows ESs and ISs to discover each other. IS-IS provides routing between ISs only.

DECnet Phase IV Prime supports inherent MAC addresses, which allows DECnet nodes to coexist with systems running other protocols that have MAC address restrictions.

DECnet support on Cisco routers includes local-area and wide-area DECnet Phase IV routing over Ethernet, Token Ring, FDDI, and serial lines (X.25, Frame Relay, SMDS). The following are the specifics of Cisco's support:


The Cisco IOS software supports packet forwarding and routing for ISO CLNS on networks using a variety of data link layers: Ethernet, Token Ring, FDDI, and serial.

You can use CLNS routing on serial interfaces with HDLC, PPP, Link Access Procedure, Balanced (LAPB), X.25, SMDS, or Frame Relay encapsulation To use HDLC encapsulation, you must have a router at both ends of the link. If you use X.25 encapsulation, you must manually enter the network service access point (NSAP)-to-X.121 mapping. The LAPB, SMDS, Frame Relay, and X.25 encapsulations interoperate with other vendors.

Cisco's CLNS implementation also is compliant with the Government Open Systems Interconnection Profile (GOSIP) Version 2.

As part of its CLNS support, Cisco routers fully support these ISO and American National Standards Institute (ANSI) standard.

Both the ISO-developed IS-IS routing protocol and Cisco's ISO Interior Gateway Routing Protocol (IGRP) are supported for dynamic routing of ISO CLNS. In addition, static routing for ISO CLNS is supported.

Note Cisco access servers currently support only ES-IS, but not IS-IS.


The XNS protocols, which were developed by the Xerox Corporation, are designed to be used across a variety of communication media, processors, and office applications. Ungermann-Bass, Inc., (now a part of Tandem Computers) adopted XNS in developing its Net/One XNS routing protocol. Standard XNS routing uses the Routing Information Protocol (RIP) update packets and the hop count metric. Ungermann-Bass Net/One uses hello packets and a path-delay metric.

Cisco provides a subset of the XNS protocol stack to support XNS routing. XNS traffic can be routed over Ethernet, FDDI, and Token Ring LANs, as well as over point-to-point serial lines running HDLC, LAPB, X.25, Frame Relay, or SMDS.

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