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Anonymous
N/A

EIGRP over routed link

Perhaps this is a daft question, but any assistance would be very much appreciated.

I have two switches which I have setup independantly with a routed link between them. I.e. No switchport on an interface and assigned them both an ip address in a /30 range.

I then would like to run eigrp between these two switches, however seem to be struggling.

I have a very basic eigrp config for the purpose of testing. In essence:

router eigrp 100

     no auto-summary

     network xxx.xxx.xxx.xxx

When run a debug and plug a device into an access port on the switch, I see console messages that indicate a HELLO was sent. On the routed port though I don't see anything in the debug messages.

If I look at eigrp interfaces (sh ip ei int) I see only the vlan interface of the switch.

Have I missunderstood something about what I'm trying to achieve, or is it just that I am missing a command.

Any help would be appreciated.

Neil

Everyone's tags (2)
8 REPLIES
Cisco Employee

EIGRP over routed link

Hello Neil,

This is interesting. Running EIGRP over a routed link between two switches should be just fine with no configuration differences whatsoever.

Please post the following outputs from each switch when configured for routed port operation:

  • show running-config interface XXX ! XXX is the routed port
  • show ip protocols
  • show ip eigrp interface

With the routed ports connected together, can you ping from one end of the routed link to the other?

Thank you!

Best regards,

Peter

Anonymous
N/A

Re: EIGRP over routed link

Hello Peter,

Thanks for your help. Yes to confirm I can ping the remote switch and vice versa.

Here is the config:

SWITCH 1 (3560-24TS-E)

interface GigabitEthernet0/1

description -- Routed Link --

no switchport

ip address 10.1.10.1 255.255.255.252

end

*** IP Routing is NSF aware ***

Routing Protocol is "eigrp 100"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Default networks flagged in outgoing updates
  Default networks accepted from incoming updates
  Redistributing: eigrp 100

Address Family Protocol EIGRP-IPv4:(100)
  EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
  EIGRP maximum hopcount 100
  EIGRP maximum metric variance 1
  EIGRP NSF-aware route hold timer is 240
  EIGRP stub, connected, summary
  Topologies : 0(base)

  Automatic network summarization is not in effect
  Maximum path: 4
  Routing for Networks:
    192.168.51.0/25
  Routing Information Sources:
    Gateway         Distance      Last Update
  Distance: internal 90 external 170

EIGRP-IPv4:(100) interfaces for process 100

                        Xmit Queue   Mean   Pacing Time   Multicast    Pending
Interface        Peers  Un/Reliable  SRTT   Un/Reliable   Flow Timer   Routes
Vl1                0        0/0         0       0/1            0           0



Heres switch 2:

SWITCH 2 (3560-24-PS-E)

interface FastEthernet0/1

no switchport

ip address 10.1.10.2 255.255.255.252

end

*** IP Routing is NSF aware ***

Routing Protocol is "eigrp 100"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Default networks flagged in outgoing updates
  Default networks accepted from incoming updates
  Redistributing: eigrp 100
  EIGRP-IPv4 Protocol for AS(100)
    Metric weight K1=1, K2=0, K3=1, K4=0, K5=0
    NSF-aware route hold timer is 240
    Router-ID: 192.168.75.1
    Topology : 0 (base)
      Active Timer: 3 min
      Distance: internal 90 external 170
      Maximum path: 4
      Maximum hopcount 100
      Maximum metric variance 1

  Automatic Summarization: disabled
  Maximum path: 4
  Routing for Networks:
    192.168.75.0
  Routing Information Sources:
    Gateway         Distance      Last Update
  Distance: internal 90 external 170

EIGRP-IPv4 Interfaces for AS(100)

                        Xmit Queue   Mean   Pacing Time   Multicast    Pending

Interface        Peers  Un/Reliable  SRTT   Un/Reliable   Flow Timer   Routes

Vl2                0        0/0         0       0/1            0           0


Apologies for the lengthy post!

Neil

Cisco Employee

Re: EIGRP over routed link

Hi Neil,

No need to apologize, it is me who asked for the lengthy output and I am perfectly fine with it!

I guess I see the problem - it's a trivial one. Your routed link is 10.1.10.0/30 but your EIGRP configuration does not have this network configured using the network command. That is why your switches do not even attempt to talk together using EIGRP on this link.

Add the network 10.1.10.0 0.0.0.3 command to the EIGRP configuration on both switches and see if the EIGRP adjacency comes up.

Best regards,

Peter

Anonymous
N/A

Re: EIGRP over routed link

Peter,

Thanks very much - this has done the trick.

If I may scope creek a little on the original request. Are you able to summarise the limitation of eigrp stubs please?

I am not seeing the networks on my 3560 S on the E. From what I understood of stub this should still work?

Thanks,
Neil

Cisco Employee

Re: EIGRP over routed link

Hi Neil,

You are welcome

Regarding EIGRP Stub routers, their operation is modified in the following ways:

  • As they establish adjacencies with other routers, they indicate (using specialized TLV records in Hello packets) their stub status. If their neighbors understand that indication, they will never forward a query towards stub routers. This helps to limit the query depth and also prevents stub routers from becoming transit routers for traffic.
  • Even if a stub router receives a query, it will always respond with a Reply containing an unreachable metric. This augments the previous point with regards to older neighbors that do not recognize the stub indication.
  • A stub router never advertises networks it learned via EIGRP itself. This also complements the basic requirement that a stub router should never appear as a (possible) transit router.

Please feel welcome to ask further!

Best regards,

Peter

Anonymous
N/A

Re: EIGRP over routed link

Thanks Peter.

My understanding of stubs was your last point, where by the wouldn't forward learned networks...

In my case, are you able to clarify perhaps why my 3560 S isn't advertising it's own network (192.168.51.0/25). On the console of the IPBase switch I see the below message. It could be unrelated as I don't believe in my case (Switch connected to switch) stub routing should be an issue...

Mar  1 18:47:56.116: EIGRP-IPv4(Default-IP-Routing-Table:100): 192.168.75.0/24 - denied by stub


Neil

Anonymous
N/A

Re: EIGRP over routed link

This was just me being daft - The vlan interface for the missing route wasn't up...

All sorted now.

Thanks again Peter.

Cisco Employee

Re: EIGRP over routed link

Hello Neil,

The IP Base image has deliberate limitations in its EIGRP implementation and supports only EIGRP stub routing. But I see no reason why the directly connected network should not be advertised.

Perhaps it is necessary to explicitly configure your EIGRP process as a stub process and allow the directly connected networks to be advertised. Try to enter the following commands:

router eigrp 100

  eigrp stub connected summary

and see if this helps.

Best regards,

Peter

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