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GeneBeamer
Beginner

Eigrp reading network statements wrong.

This is what I am seeing on my router...

router eigrp 100
network 10.1.16.0 0.0.0.255
network 10.1.17.0 0.0.0.255
network 10.1.64.0 0.0.0.255
network 10.1.249.0 0.0.0.3
network 10.1.249.16 0.0.0.3
network 10.1.250.0 0.0.0.255
network 10.1.253.1 0.0.0.0
network 172.17.0.0 0.0.7.255 - - Wrong subnet
network 172.17.44.0 0.0.0.7 - - Wrong Subnet
network 172.17.50.0 0.0.0.255
network 172.17.200.0 0.0.3.255
eigrp router-id 10.1.253.1

The Vlan setup for 172.17.0.0 is with the subnet of 255.255.252.0 but thats not what the wildcard says.....

The Vlan setup for 172.17.44.0 is with the subnet of 255.255.252.0 but thats not what the wildcard says......

So when I do a sho ip route this is what I get for both.....

sho ip route 172.17.44.1
Routing entry for 172.17.44.0/22
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Redistributing via eigrp 100
  Routing Descriptor Blocks:
  * directly connected, via Vlan401
      Route metric is 0, traffic share count is 1

sho ip route 172.17.0.1
Routing entry for 172.17.0.0/22
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Redistributing via eigrp 100
  Routing Descriptor Blocks:
  * directly connected, via Vlan100
      Route metric is 0, traffic share count is 1

How is EIGRP reading these as a /22 when the network statements say one is a /21 and the other is a /29 ??  I am so confused and I don't know if I need to fix these and what this issue maybe causing... Any input would be Awesome...   This router is setting in a multi-router enviroment.

12 REPLIES 12
Martin Parry
Participant

Hi

The router is seeing these as /22 as they are directly connected and it knows what the subnet mask is as it is locally configured on the device itself.

Hope this helps

Martin

I thought that the only thing telling the router to forward routes would be the network statement.. However, because it is directly connected it looks at the vlan information instead of the EIGRP statement?

Hi

The network statements within EIGRP config are not telling the local router how to forward traffic, they are telling the router what to advertise out to it's neighbours.

The router will decide how to route traffic based on the information within it's routing table.  If you do a show ip route and look at the output you will see all the networks / subnets that the router is aware of.  These entries will be learnt in a number of ways and any locally originated networks eg: those residing on interfaces on the local device (VLAN SVIs in your case) will be preferred over any other potential entry.

Hope this helps

Martin

It looks like you have some auto summarization issues here.  Did you include the 'no auto-summary' command in your router eigrp 100 configuation and omit it from the posted config?

Yes i did leave out the auto summary statement from the posted..

router eigrp 100
network 10.1.16.0 0.0.0.255
network 10.1.17.0 0.0.0.255
network 10.1.64.0 0.0.0.255
network 10.1.249.0 0.0.0.3
network 10.1.249.16 0.0.0.3
network 10.1.250.0 0.0.0.255
network 10.1.253.1 0.0.0.0
network 172.17.0.0 0.0.7.255
network 172.17.44.0 0.0.0.7
network 172.17.50.0 0.0.0.255
network 172.17.200.0 0.0.3.255
eigrp router-id 10.1.253.1
no auto-summary

The problem I have with what you suggestion Martin Parry is this output from another router when i do sho ip route. This router is telling others I have the 172.17.44.0 /22 network when it DOES but it's not in the EIGRP statement. ( Also note that EIGRP isnt a strong area of mine ).

sho ip route 172.17.44.1
Routing entry for 172.17.44.0/22
  Known via "eigrp 100", distance 90, metric 31232, type internal
  Redistributing via eigrp 100
  Last update from 10.24.249.x on Vlan802, 2d01h ago
  Routing Descriptor Blocks:
  * 10.24.249.17, from 10.24.249.x, 2d01h ago, via Vlan802
      Route metric is 31232, traffic share count is 1
      Total delay is 220 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 12/255, Hops 3

According to your output these routes are redistributed by the routing protocol.

sho ip route 172.17.44.1
Routing entry for 172.17.44.0/22
  Known via "connected", distance 0, metric 0 (connected, via interface)
Redistributing via eigrp 100
  Routing Descriptor Blocks:
  * directly connected, via Vlan401
      Route metric is 0, traffic share count is 1

sho ip route 172.17.0.1
Routing entry for 172.17.0.0/22
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Redistributing via eigrp 100
  Routing Descriptor Blocks:
  * directly connected, via Vlan100
      Route metric is 0, traffic share count is 1

Is there a 'redistribute connected' command in your EIGRP config?  That would fully advertise the connected networks whether they have smaller scoped network statements or not.

Not on this router however on another network there is a  redistribute static metric 1 1 1 1 1  command with a statement of network 172.17.44.0 0.0.3.255

Hi

Sorry for the delay, I've been on the tube.

The network statement within EIGRP does not specify what is actually advertised but more specifies what interfaces will participate and be advertised.

For instance if you had four interfaces with ip addresses as follows:

172.17.0.0 /24

172.17.1.0 /24

172.17.2.0 /24

172.17.3.0 /24

You could insert a network statement of

Network 172.17.0.0 0.0.3.255

This would mean that the configured ip subnets all interfaces within this network statement would be advertised to the neighbour routers along with their subnet masks. The router would still advertise the individual subnets as opposed to the aggregated /22. So the receiving router would learn the 4 subnets

If however you had 5 interfaces Such as:

172.17.0.0 /24

172.17.1.0 /24

172.17.2.0 /24

172.17.3.0 /24

172.17.4.0 /24

And inserted the same network statement into EIGRP:

Network 172.17.0.0 0.0.3.255

Only the first 4 subnets would be advertised. Not the 5th.

Hope this helps

Martin

Sent from Cisco Technical Support iPhone App

tj.mitchell