Routing/Topology table

Answered Question

HI Experts!

what is the difference betwwen the Routing table & the Topology table in EIGRP?

10xs for ur great info.

I have this problem too.
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Correct Answer by Richard Burts about 9 years 7 months ago

Ali

The EIGRP protocol builds a topology table based on the advertisements that it receives from neighbors. Everything that EIGRP learns goes into the topology table, whether it is a route that actually gets used (has the best metric) or a route with a worse metric that will not actually be used. EIGRP looks through the topology table to find the best route, based on the metric (bandwidth and delay by default). EIGRP then gives its best routes to the process that manages the routing table.

The routing table is maintained by a separate process and not by EIGRP, or OSPF, or BGP, or RIP or any of the routing protocols. The process receives information from each protocol about its best routes. When the protocol managing the routing table receives the same prefix from 2 different protocols then it uses administrative distance to decide which one to put into the routing table.

So the routing table is used to make forwarding decisions for IP packets. The routing table may contain information from multiple protocols. The EIGRP topology table is not used to make forwarding decisions for IP packets. It is used by EIGRP to accumulate information about all the prefixes advertised by any EIGRP neighbor and to identify the best routes that EIGRP has learned.

HTH

Rick

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purohit_810 Thu, 02/22/2007 - 10:57

Hi,

See all are the Link state protocols maintain three tables for each routed protocols.

1) Routing 2) Naighbor informayion 3) Topology table

When Eigrp contact to Neighbors with Hello packet and establishing neighbo relationship....Neighrbor is sending whole TOPOLOGY TABLE.. from that topology table... it is FILTERING BEST ROUTE FOR EACH REMOTE NETWORK and that it PLACE INTO ROUTING TABLE.

NOW ROUTING TABLE HAS ALL SUCCESSOR ROUTE.

In simple words we can say

Topology table contains with all physibal successor routes.

Routing table is full of with successor (PRIMARY)routes.

Regards,

Dharmesh Purohit

Correct Answer
Richard Burts Thu, 02/22/2007 - 11:03

Ali

The EIGRP protocol builds a topology table based on the advertisements that it receives from neighbors. Everything that EIGRP learns goes into the topology table, whether it is a route that actually gets used (has the best metric) or a route with a worse metric that will not actually be used. EIGRP looks through the topology table to find the best route, based on the metric (bandwidth and delay by default). EIGRP then gives its best routes to the process that manages the routing table.

The routing table is maintained by a separate process and not by EIGRP, or OSPF, or BGP, or RIP or any of the routing protocols. The process receives information from each protocol about its best routes. When the protocol managing the routing table receives the same prefix from 2 different protocols then it uses administrative distance to decide which one to put into the routing table.

So the routing table is used to make forwarding decisions for IP packets. The routing table may contain information from multiple protocols. The EIGRP topology table is not used to make forwarding decisions for IP packets. It is used by EIGRP to accumulate information about all the prefixes advertised by any EIGRP neighbor and to identify the best routes that EIGRP has learned.

HTH

Rick

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