LDP and SR

[rocky2022]

Hello,

I am enabling SR with OSPF and I am issuing sr-label-preferred command under segment-routing mpls section in asr920 (ios-XE)

but when i am checking output in show mpls interfaces, its still showing (ldp) on uplink bdi4

mpls ip command is there on bdi4

mpls ldp neighbor x.x.x.x password abcd

so i am not understanding why we need ldp stuff if we are preferring segment-routing ?

I can see SR preferred under show segment-routing attributes

please help me to understand.

[rocky2022]

after removal of ldp commands from asr920, show mpls forwarding-table showing many routes with no label even though segment-routing is enabled on device. what could be the scenario here?

[Harold Ritter]

Hi @rocky2022 ,

Can you post the SR configuration from one of the devices.

Regards,

[Harold Ritter]

Hi @rocky2022 ,

Do you see labels in the "show mpls forwarding" for the devices that are SR enabled?

Regards,

[Harold Ritter]

Hi @rocky2022 ,

On the ASR920, when you do a "show mpls forw", do you see labels for the AGG9912 in SCSG?

Regards,

[rocky2022]

Hello Harold,

I Will check while doing migration tomorrow after removal of LDP stuff from asr920 and will keep only SR.

[Harold Ritter]

Hi @rocky2022 ,

Just to mention that it is fine to have 2 SR islands (separated by LDP) communicating with each other. If SR only devices need to communicate with LDP only devices, then a SR Mapping server need to be configured on one or more of the SR enabled devices.

Regards,

[rocky2022]

Hello Harold,

Please find below configuration from ASR920

ASR920 (CSG) -----SCSG (Pre-Agg)-----AGG 9912-----Core ASR9922-------------AGG9912--SCSG--CSG

|----------------------SR--------------------  |----------------LDP-----------|----------SR----|

mpls ldp neighbor 10.3.6.66 password tecom

10.3.6.66 - SCSG
segment-routing mpls
set-attributes
address-family ipv4
sr-label-preferred
exit-address-family
!
global-block 18500 32750
!
connected-prefix-sid-map
address-family ipv4
10.3.6.204/32 index 5309 range 1
exit-address-family

We have LDP config on CSG - ldp neighbor IP of SCSG device, not sure why we need this?

[smailmilak]

Hi, what does this say 

show segment-routing mapping-server prefix-sid-map ipv4 detail

Do you really want only 1 prefix SID for the LDP domain?

[rocky2022]

Hello Smailmilak,

Do you really want only 1 prefix SID for the LDP domain? -------Means ?  i have very little idea about SR for now

[smailmilak]

My advice is to go through those tutorials and to configure SR then. 

https://www.segment-routing.net/srmpls-tutorials

Full configs of your devices would be helpful as well.

[Harold Ritter]

Hi. @rocky2022 ,

Could you please confirm the routing protocol you run and include the configuration.

Regards,

[rocky2022]

Hello Harold,

Please find below OSPF config:

router ospf 100
router-id 10.3.6.208
auto-cost reference-bandwidth 100000
log-adjacency-changes
nsf ietf
segment-routing area 0.0.2.45 mpls
segment-routing mpls
fast-reroute per-prefix enable area 0.0.2.45 prefix-priority low
fast-reroute per-prefix ti-lfa
fast-reroute per-prefix ti-lfa area 0.0.2.45
area 0.0.2.45 authentication message-digest
area 0.0.2.45 nssa
timers throttle spf 50 100 1000
timers throttle lsa 10 1000 1000
timers lsa arrival 15
timers pacing flood 15
passive-interface Loopback0
network 10.197.9.158 0.0.0.1 area 0.0.2.45
network 10.3.6.208 0.0.0.0 area 0.0.2.45
bfd all-interfaces