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Routing - odd behaviour

Not applicable

I'm hoping somebody can point me in the right direction for a problem I'm experiencing... I have attached a basic diagram to hopefully make sense of my explanation of the problem.

I have 3 3560 switches which are configured with trunks between them. They run vlan 10, 11 & 12.

I have a 'core' switch (switch 1) of these 3 to which an MPLS router is connected on vlan12.

I in addition have another switch hanging off the 'core' switch via a routed link (switch 4). I have EIGRP configured as a stub and as such the IP address on the routed link at the core switch end is of a /24 from vlan 1 on the other switch. This makes the route directly connected and therefore distributed via EIGRP stubs.

Switch 1 is then exchanging routes with the MPLS router (via EIGRP).

The problem I have is that from any subnet on any switch (switch 1, 2 or 3) I can ping 192.168.13.1 (switch 4). When I try and ping switch 4 from over the MPLS I am unable to. If I trace to the switch I see it reaches the outside of the MPLS router, but is then unresponsive. The same applies if I try to ping switch 1 on 192.168.13.2. Any of the other IP addresses of switch 1 respond.

The MPLS network is a managed solution to which I have no access. I'm told that the MPLS provider is able to ping switch 1 & switch 4 on the 192.168.13.x addresses from a remote router (192.168.32.2). I have tried from a switch on the same L2 subnet (192.168.32.1) and I don't get a response.

From switch 4 I am able to ping the switch on 1 of it's interfaces (192.168.19.1), but not the interface I mentioned above 192.168.32.1

There are no access lists in place on the switches and no firewalls between the sites.

I have no idea where to start troubleshooting this, and any assistance would be much appreciated.

Thanks,

Neil

Diagram.jpg

22 Replies 22

Peter Paluch
Hall of Fame Cisco Employee Hall of Fame Cisco Employee
Hall of Fame Cisco Employee

Hi Neil,

A couple of questions and remarks - please go over each of them carefully:

  • Your exhibit contains duplicate addresses 192.168.10.2/24, 192.168.11.2/24 and 192.168.12.2/24 indicated by switches 1 and 2. Is it a typo or do these switches indeed have the same IP address? That would be a conflict of IP addresses.
  • The 10.1.10.1 address is not indicated in your exhibit but I assume that is configured on some other interface of switch 4.
  • I assume that the routed link between switch 1 and switch 4 is using the IP address 192.168.13.0/24 with switch 4 being .1 and switch 1 being .2. Is that correct?
  • From switch 4, can you ping 192.168.12.254? (I assume that 192.168.12.254 is the IP address of the MPLS router)
  • From switch 4, can you ping 192.168.12.254 if you use the source IP address 10.1.10.1? Use the ping 192.168.12.254 source 10.1.10.1 command to accomplish this.
  • When you enter the show ip eigrp topology command on switch 1, do you see the networks 192.168.3.0/24 and 10.1.10.0/x being present? Can you post this output here? You may delete the irrelevant networks from this output.
  • Is the EIGRP neighborship between switch 1 and the MPLS router working? Check that with show ip eigrp neighbor command.
  • Can you post the EIGRP configuration from switch 1 here please?

Thank you!

Best regards,

Peter

Hello Peter - thanks for your response.

  • Your exhibit contains duplicate addresses 192.168.10.2/24, 192.168.11.2/24 and 192.168.12.2/24 indicated by switches 1 and 2. Is it a typo or do these switches indeed have the same IP address? That would be a conflict of IP addresses.
  • The 10.1.10.1 address is not indicated in your exhibit but I assume that is configured on some other interface of switch 4.

Apologies - both of these were mistakes in the example addresses I've given. I have since corrected the diagram and original post.

  • I assume that the routed link between switch 1 and switch 4 is using the IP address 192.168.13.0/24 with switch 4 being .1 and switch 1 being .2. Is that correct?

This is correct.

  • From switch 4, can you ping 192.168.12.254? (I assume that 192.168.12.254 is the IP address of the MPLS router)

Yes, I can ping the router, and in fact can ping other sites, however not all subnets at other sites. As I breifly explained above, I am able to ping a switch at a remote site on 1 vlan interface, but not others.

  • From switch 4, can you ping 192.168.12.254 if you use the source IP address 10.1.10.1? Use the ping 192.168.12.254 source 10.1.10.1 command to accomplish this.

As you highlighted the 10.1.10.1 address was incorrect. I have updated the example above, but this address should have been 192.168.13.1. I have since corrected this, but 10.1.10.1 doesn't exist.

This is the only IP address on switch 4 so the result is the same as the above point. It is successful.

I have however tested this on switch 1 using ping 192.168.12.254 source gigabitEthernet0/4 and this fails.

  • When you enter the show ip eigrp topology command on switch 1, do you see the networks 192.168.3.0/24 and 10.1.10.0/x being present? Can you post this output here? You may delete the irrelevant networks from this output.
  • Is the EIGRP neighborship between switch 1 and the MPLS router working? Check that with show ip eigrp neighbor command.
  • Can you post the EIGRP configuration from switch 1 here please?


Heres the eigrp topology output for 192.168.13.0/24. As mentioned above 10.1.10.0 was a typo and doesn't exist. This is a directly connected route however, switch 1 & switch 4 are not exchanging routes via eigrp.

EIGRP-IPv4 Topology Entry for AS(100)/ID(192.168.12.2) for 192.168.13.0/24

State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2816

Descriptor Blocks:

0.0.0.0 (GigabitEthernet0/4), from Connected, Send flag is 0x0

Composite metric is (2816/0), route is Internal

Vector metric:

Minimum bandwidth is 1000000 Kbit

Total delay is 10 microseconds

Reliability is 255/255

Load is 1/255

Minimum MTU is 1500

Hop count is 0

Originating router is 192.168.12.2

I have confired the neighbour relationship is ok. Other routes are currently advertised out of this site. It is a production site and I'm only experiencing issues with the subnet over the routed link.

Here is the eigrp config from switch 1.

router eigrp 100

distribute-list EIGRP_RECIEVE in

network 192.168.0.0 0.0.255.255

passive-interface default

no passive-interface Vlan12

eigrp stub connected summary

I hope the above makes some sense. Anything else that you need, please let me know.

Thanks,
Neil