04-01-2020 04:01 AM
Hello everyone.
I am racking my brain over something that hopefully has a very simple answer.
I have routers linked in a sequential chain with some networks at either end.
Originally they were using eigrp as the routing protocol and I configured MPLS.
Using wireshark I could verify that pings from workstations which traveled through these routers was MPLS encapsulated.
I then removed the EIGRP and configered BGP and with MPLS remaining the same.
Pings works. BGP neighbors are fine. MPLS neighbors are fine. But there isnt any info in the MPLS forwarding table and wireshark is not showing MPLS encapsulation anymore.
What am I doing wrong?
Many thanks
Solved! Go to Solution.
04-01-2020 09:42 AM
Ok cool thanks for sharing your config.
The problem is that LDP does assign labels to IGP learned prefixes, which makes sense because BGP is not a routing protocol and does not ensure reachability between devices, in fact it only shares prefixes without any notion of routing in between. Imagine if LDP would have assigned labels to any prefix, imagine the blackholes :)
More context: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_ldp/configuration/xe-16-7/mp-ldp-xe-16-7-book/mp-ldp-alloc-filter.html
Hope ti helps.
Cheers, L.
04-04-2020 01:41 PM
04-01-2020 06:44 AM
You do not use BGP as IGP. It's an application, not a routing protocol and typically needs an underlying IGP/static-route configured in the network for reachability purposes.
That said, it's hard to imagine how your network setup works just reading your description. For instance there's no such thing as MPLS adjacency, perhaps you meant LDP?
I'd be happy to tak a look iuf you can post a chunck of your config :)
Cheers, L.
04-01-2020 07:27 AM
04-01-2020 09:10 AM
04-01-2020 09:42 AM
Ok cool thanks for sharing your config.
The problem is that LDP does assign labels to IGP learned prefixes, which makes sense because BGP is not a routing protocol and does not ensure reachability between devices, in fact it only shares prefixes without any notion of routing in between. Imagine if LDP would have assigned labels to any prefix, imagine the blackholes :)
More context: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_ldp/configuration/xe-16-7/mp-ldp-xe-16-7-book/mp-ldp-alloc-filter.html
Hope ti helps.
Cheers, L.
04-01-2020 10:43 PM - edited 04-02-2020 12:27 AM
Hi Guys,
Thank you very much for your responses.
The send-label command has made it work!
As you can tell this scenario was through a simulator but I asked the question because I wanted to know why it wasnt working.
At first I was somewhat puzzled by some of the responses on here regarding BGP not being a routing protocol. And I actually still am to an extent. If I recall correctly from my teaching a BGP network will only show up in the RIB if there is already a known path to it. This would be via a static or IGP route so I guess that somewhat explains it actually.
My BGP neighbors are not discovered by static routing but but via the connected interfaces.
If my BGP neighbors were configured via loopbacks and static routes would MPLS tagging have been used by default?
Also one more question please if I may. On one router when configuring I enabled MPLS before I had configured the label range. I fixed this by rebooting the router afterwards and the labels I wanted were then in effect. Is there any command I can use to do this without rebooting? I had already tried the clear ldp counters and bindings. I cant remember all the clear commands I used but none were effective.
Thank you
04-02-2020 02:12 AM
04-04-2020 01:40 PM
04-04-2020 01:41 PM
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