LDP and Segment Routing IOS XE

[imanless]

Hello all. I am a novice when it comes to segment routing. I have a simple network in which one region has LDP enabled and the other region has SR enabled. I want the SR Enabled routers to have the Node or Prefix-SID for the devices outside of the SR Domain, (meaning the devices in LDP). I tried to set up a mapping server, but I am using XE Routers now, not XR (for which it worked). Can someone guide me if there is anything extra one has to do when using XE Routers e.g: CSR1000v. 

I am using R4 for my mapping server. The routers inside the SR Domain have routes to the routers inside the LDP Domain.

[balaji.bandi]

what version of CSR1000V  ?

as per i know last time i tested with CSR1000v it was not worked ( as you mentioned IOS XR is good candidate to test )

This may have changed in latest CSR1000V - how does your config looks like ?

[imanless]

I am using Version 17.03.06

[Harold Ritter]

Hi @imanless ,

The SR mapping server feature is helpful only if the two domains are running as one IGP domain. Is that your case? If the two domains are running as separate IGP domains, you can use BGP LU to provide connectivity between them.

Regards,

[imanless]

I am running ospf process 1 in the segment routing region and ospf process 2 in the LDP region. They are both in area 0. And they can ping each other, as I have redistributed loopbacks into each other's regions. But the SR enabled routers are not coming up with the Prefix-SID for the destination router outside the SR Domain, meaning the ones in the LDP Region.

[Harold Ritter]

Hi @imanless ,

Try running one IGP domain without redistribution between the two. This is the use case for the Segment Routing mapping server (SRMS). SRMS has been created for customers who want to migrate from LDP to SR within the scope of one single IGP domain.

Regards,

Regards,

[imanless]

I made it one single domain and then issued these commands on R4.

segment-routing mpls
!
connected-prefix-sid-map
address-family ipv4
4.4.4.4/32 absolute 16004 range 1
exit-address-family
!
!
mapping-server
!
prefix-sid-map
address-family ipv4
5.5.5.5/32 absolute 16005 range 1
6.6.6.6/32 index 9 range 1
exit-address-family

All the routers have ospf reachability in area 0. But the segment routing region doesn't generate any labels for the destinations outside of the SR Domain. 

[Harold Ritter · Accepted solution]

Hi @imanless ,

> But the segment routing region doesn't generate any labels for the destinations outside of the SR Domain. 

How did you determine that the mapping-server is not working?  You can run the following command on the mapping server to validate that it advertises the appropriate prefix/label combination.

show segment-routing mpls mapping-server ipv4

Did you configure the following command under ospf?

router ospf xxx

segment-routing prefix-sid-map advertise-local

After configuring the above command, you should be able to see the prefix/label pairs being advertised to other SR routers with the following command:

show segment-routing mpls mapping-server ipv4

Regards,

[imanless]

Dear @Harold Ritter 

Thanks a lot. I was not using the advertise-local command under the ospf process. It worked. Thank again. Your support means a lot.

[Harold Ritter]

You are very welcome @imanless and thanks for the feedback

[MHM Cisco World]

7. LDP and SR co-existence part1: LDP to SR migration - RAYKA (rayka-co.com)