Chapter Contents |
Previous |
Next |
Protocols |
All popular routing protocols are based on one of the following distributed algorithms:
In link state algorithms, routers determine their neighbors (and the cost to each) by exchanging hello packets. They then construct link state packets containing a list of their neighbors (and associated costs) and flood these packets throughout the entire domain. Using the link state packets, the routers can construct a graph of the network and then calculate the "best" paths through it. Link state algorithms converge more quickly than distance vector algorithms, but this typically require more memory and CPU processing than distance vector algorithms.
The netWorks application provides simulations of two link state protocols:
The IS-IS and OSPF protocols both elect a Designated Router (DR) on LANs with more than one router attached to them. The protocols typically use the router's priority and router ID in the DR selection process. The DR is responsible for collecting and distributing the link state information for all the routers on its LAN throughout its area. This helps reduce the protocol traffic on the network. In the OSPF routing protocol, a Backup Designated Router (BDR) is also elected to take over should the DR fail. The following sections provide a brief overview of the IS-IS and OSPF routing protocols.
Chapter Contents |
Previous |
Next |
Top |
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.