eigrp

Unanswered Question
May 26th, 2007

hai all

1. if an eigrp router which have no downstream neigbor (leaf router ) receives a query and if the router dont have a feasible successor,then it would give an eigrp reply with the route as unreachable.

(a)will the router then remove the route from its routing table/topology table immediately??

or

(b)it keeps the route in routing table/topology table and sends a reply as unreachable ,and then the router which originated the query, after receiving all the reply for the query and finding that its not reachable will remove from its tables and will send an update stating that the route is unreachable to its neighbor,and hence the leaf router removes it from the table.

which of the abv happens or is it something else happens??

if (a) happens ,eigrp update is said to be also send when a link fail(or route not reachable).if the other router learns the unreachable routes as on case (a),then why update needed to be send..??

2.what are the contents of an eigrp query/reply pck(know that both have a type code of 3 and 4 respc)??

3.eigrp updates are said to be bounded,ie it sends only to affected neighbors.how it comes to know who all will be affected by routers..??

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3 (1 ratings)
Loading.
Amit Singh Sat, 05/26/2007 - 22:28

Hi Arun,

When an EIGRP router recieves a Query and it doesnot have feasible successor, it will start the diffusing computation and will mark the route as an "Active route ". It will start a, "Active timer " and query all its neighbors. If the router doesnot have any neighbor or doesnot get the appropriate reply before the timer expire, it marks the route with an infinite metric and sends a reply to the upstream neighbor. The EIGRP router which originated the Diffusing computation will mark the route as reachable with infinite metric and will update all of its neighbors. The router which replies back with a route to reach the destination will be selected as a successor.

2. Eigrp quer/reply are included in the EIGRP packet types and are represented by opcode in that packet header. They both contains, flags,sequence,AS number etc. whic are a part of the EIGRP packet.

3.Eigrp updates are bounded and it determines that by using its topology table and neighbor table.If an EIGRP routers request for an update the EIGRP updates are unicast. But when it is requested by multiple routers such as metric change for a route or topology change, it is multicasted at 224.0.0.10 ip address.

HTH,please rate if it does.

-amit singh

s.arunkumar Sun, 05/27/2007 - 01:11

thanks amit for ur reply...

As your answer states the router will send a reply with infinite metric if it dont have a feasible successor..

1.my doubt is will it remove the entry from the topology table and send eigrp reply or it will keep the entry as

with infinite metric and will only remove when it gets an eigrp update abt the route from its upstream router as

unreachable(or with infinite metric) ???

2.Is that whenever a link state or its parameter changes first the router performs a local computation,if fails then a diffuse computaion(which includes sending and receiving of eigrp query and replies) and finally only the eigrp updates are send based on the result...am i right???

regards

arun :)

Amit Singh Sun, 05/27/2007 - 09:41

Arun,

1. The router which originated the diffusing computation will finally remove the route from its table and update all of its neighbors.

2. Yes, you are right about it.

HTH,

-amit singh

s.arunkumar Sun, 05/27/2007 - 20:51

ok :)

u mensioned that "Eigrp updates are bounded and it determines that by using its topology table and neighbor table . "

Now topology tables have info abt there successors and feasible successors(or upstream routers for routes).and neighbor tables have info abt their eigrp neighbors.So an update that generated on a event such as link failure etc will be send to all its neighbors,ie ,using its neighbor table.but,how topology table helps in sending bounded updates as all the info. is abt there upstream routers???

sorry if i am asking anything stupid...actually i am confused abt the bounded updates,which states that updates are send to only affected neighbors.Isn't that all the neighbors would be affected??ie,isnt it better to say updates are send to all neighbors(after considering split horizon)....

regards

arun :)

Amit Singh Sun, 05/27/2007 - 21:33

Hi Arun,

The way that only the routers that are interested on the updates can take them and put

them up in their table is through multicast packets, EIGRP talks in muticast address 224.0.0.10, and in each packet the information of the source router, with AS number is attached to each packet so that how the updates only affect some routers within the same AS number.The EGIRP updates are bounded within a single AS.

-amit singh

Actions

This Discussion