Specifications

Chapter 1. Router Concepts 17
Numerous network protocols have evolved, and within each protocol are associated protocols for routing, error
handling, network management, etc. The following chart displays the networking and associated protocols
supported by the router.
Bridging
Bridging connects two or more LANs so that all devices share the same logical LAN segment and network
number. Transparent bridging allows locally connected devices to send frames to all devices as if they were local.
The MAC layer header contains source and destination addresses used to transfer frames. An address table is
dynamically built and updated with the location of devices when frames are received. (To see the contents of the
bridging table, use the command bi list , page 189.)
Bridging allows frames to be sent to all destinations regardless of the network protocols used. It allows protocols
that cannot be routed (such as NETBIOS) to be forwarded and allows optimizing internetwork capacity by
localizing traffic on LAN segments. A bridge extends the physical reach of networks beyond the limits of each
LAN segment. Bridge filtering can increase network security.
The router bridging support includes the IEEE 802.1D standard for LAN-to-LAN bridging and the Spanning Tree
Protocol for interoperability with other vendorsÕ bridge/routers. Bridging is provided over PPP as well as adjacent
LAN ports.
Bridge-Only Units
A series of bridge-only units is available, both upgradable and non-upgradable. An upgradable bridge can be
upgraded to a router; a non-upgradable bridge cannot.
Network Protocol Associated Protocols Description
Internet Protocol
(IP)
Routing Information Protocol (RIP) Maintains a map of the network
Address-Resolution Protocol (ARP) Maps IP addresses to datalink
addresses
Reverse Address Resolution Protocol (RARP)
a
a Used only during a network boot.
Maps data-link addresses to IP
addresses
Internetwork Control Message Protocol
(ICMP)
Diagnostic and error reporting/
recovery
Simple Network Management Protocol
(SNMP)
Network management
Internet Packet
Exchange (IPX)
Routing Information Protocol (RIP)
b
b IPX-RIP is a different protocol from IP-RIP and it includes time delays.
Maintains a map of the network
Service Advertising Protocol (SAP) Distributes information about service
names and addresses