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Routing table question about OSPF routes?

I’m looking in the routing table and I’m not sure why this is (see below):

This is part of the displayed output:

sh ip route ospf

O       146.136.94.128/25 [110/41] via 146.136.5.152, 2w0d, Vlan10
                          [110/41] via 146.136.5.151, 2w0d, Vlan10
                          [110/20] via 146.136.5.2, 2w0d, Vlan10
                         [110/20] via 146.136.5.2, 2w0d, Vlan10


Why are there two routing entries going to the same interface (146.136.5.2):
                         [110/20] via 146.136.5.2, 2w0d, Vlan10
                         [110/20] via 146.136.5.2, 2w0d, Vlan10
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dsterling
Asked:
dsterling
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4 Solutions
 
arnoldCommented:
Without knowing your setup, it might be getting two paths
i.e. 146.136.5.2 has two paths that advertise 146.136.94.128/25 So it repeats it or it is in the process of converging.
The paths are load balanced, and are preferred, it could be this is the weighted configuration.

IT could be that there are two ranges one that includes this one i.e. another segment, 146.136.94.0/24 or 146.136.0.0/16 is also advertised as accessible via 146.136.5.2
When querying for 146.136.94.128/25 both 146.136.0.0/16 and 146.136.94.128/25 fit the query and two routes are returned with the same destination.
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dsterlingAuthor Commented:
arnold,

This seems like a very good answer, but I'm having trouble being clear on understanding this and trying to verify it. Here is another example:

O       146.136.191.252/30 [110/2] via 146.136.5.3, 2w0d, Vlan10
                         [110/20] via 146.136.5.2, 2w0d, Vlan10
                         [110/20] via 146.136.5.2, 2w0d, Vlan10
                         [110/20] via 146.136.5.2, 2w0d, Vlan10
                         [110/20] via 146.136.5.2, 2w0d, Vlan10

What could I do to verify your explanation so I could better see what you mean?

Thank you
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arnoldCommented:
Do you have a wider scope?
146.136.0.0/16
146.136.194.128/25
146.136.191.252/30

are all subsets.  The routing table will usually direct the path that matches the closest when there are different paths.  in your case, all paths lead through 146.136.5.2

If you have three paths:
146.136.0.0/16 146.136.0.5
146.136.194.128/25 146.136.12.5
146.136.191.252/30 146.136.191.253

What is your OSPF peering network looks like.
You can have one device 192.168.5.2 that peers with each of the ones above, so looking at it, it reports the path to each of those segments can go through it, same cost/preference means each path has an equal weight.  You are posting a single snippet from a single node so I am not sure what exactly you are looking for in a response.


You could add a higher cost on a path such that 146.136.5.2 to lets say 146.136.12.5 as a path for 146.136.194.128/25 is very costly least prefer, and you'll see the change in the wight/preference for this segment over 146.136.5.2.
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Don JohnstonInstructorCommented:
I'm going to go with a bug.  It's definitely a duplicate entry. What does the CEF table show?

What platform and IOS version are you running?
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dsterlingAuthor Commented:
This is what is in the CEF table for the subnet:
146.136.94.128/25    146.136.5.151        Vlan10
                     146.136.5.152        Vlan10
                              
This is showing the 6413 is going to 2 Nexus 7K devices across a VPC port channel. The devices are directly connected.

Does this seem correct for the CDF table? And maybe I should get with Cisco about this?
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arnoldCommented:
You should contact Cisco.
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dsterlingAuthor Commented:
Thank you arnold, I appreciate all you expert comments.
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arnoldCommented:
Thanks, not sure the last comment was worthy of a points award.
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