EIGRP AS limitation

Unanswered Question
May 12th, 2007

Hi every body

How many EIGRP AS numbers could be defined simultaniously in a router (7206) ?

Aparently more than 30 AS is not possible .

Tanx

I have this problem too.
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mohammedmahmoud Sat, 05/12/2007 - 06:14

Hi,

The maximum number of Process Data Block (PDB) that could exist on a single router is 32 PDBs, 2 of them are static and connected, so yes you can have a max of 30 EIGRP processes with 30 ASs simultaneously on a single router.

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

Harold Ritter Sat, 05/12/2007 - 06:15

Morteza,

That is correct. There is a limitation on the number of routing processes you can run in IOS. This limit is 32. Out of this 32, one is reserved for static and another for connected routes, which leaves you with 30 processes for routing protocols as such.

Why would you need so many EIGRP instances running at once?

Note that this limitation doesn't prevent you to run as many VRF instances as you want as all the VRF instances for one routing protocol are tied to one routing protocol process instance.

Hope this helps,

MortezaSoltani Sat, 05/12/2007 - 06:34

Herriter

Tanx for response ,

We have more than 30 remote branches include of sub networks in every them . I can connect all of them using one AS but any link isolation for each branch cause routing update with a lot of traffic. So I tried to assign one AS for each branch (that has two links which are backup of each other).

Have you any other solution?

Regards

royalblues Sat, 05/12/2007 - 06:38

If you can use OSPF, then you can have these remote sites in differen areas and run a single instance.

Narayan

MortezaSoltani Sat, 05/12/2007 - 06:44

Thanks Narayan.

So, how many OSPF area can be defined simultanously in a router? Could we use some benefits of EIGRP such as load balancing in OSPF?

Thx

royalblues Sat, 05/12/2007 - 06:55

OSPF can certainly do loadbalancing like EIGRP for equal cost routes. It does not support unequal cost traffic loadbalancing

All the areas in OSPF needs to be connected to Area 0 or the backbone. Hence the backbone router should be capable to take the load. normally it is recommended to have not more than 60 routers in any one area

Narayan

Harold Ritter Sat, 05/12/2007 - 08:16

Morteza,

I'm not sure I understand why a link isolation for one branch would cause that much traffic. I have seen branch networks with much more than 30 branches using a single eigrp process.

If all you have at the remote branch is a single router then you might want to consider using the EIGRP stub routing feature to lower the routing protocol traffic generated by a link flap.

http://www.cisco.com/en/US/products/sw/iosswrel/ps1829/products_feature_guide09186a0080087026.html

Hope this helps,

royalblues Sat, 05/12/2007 - 10:13

Harold has a very good point over here..

EIGRP does not refresh the routes as OSPF(every 30 minutes) and hence the only traffic that you will see will be the hellos.

Also if the branches are configured as stub, queries are not sent therby limiting the scope.

we are succesfully running eigrp as a single instance across 20 branches

Narayan

ruwhite Mon, 05/14/2007 - 04:27

Use EIGRP stubs, as recommended elsewhere.... We have networks with over 600 EIGRP remote routers on a single hub router using EIGRP stubs and effective route filters, so 30 shouldn't be a problem.

:-)

Russ

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