User guide

16 Chapter 1. Router Concepts
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. 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 the frames are received.
Transparent bridging allows locally connected devices to send frames to all devices as if they were local.
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. Bridging can increase network security with filtering.
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.
When to Use Routing or Bridging or Both
The following charts describe the operational characteristics of the router when you enable routing, bridging, or
both routing and bridging.
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