SR-TE tunnel doesn't come UP

[markk2316]

Hey Here !,
I have the following topology consisting of 3 routers.

66.110.0.63      -> 22.22.21.22  ->  33.33.33.33
   Area - 0                  Area - 0             Area - 0 

I want to create a SR-TE tunnel in order to establish s-BFD. Now my issue is that the tunnel i've configured is DOWN under the claim that it didn't find the node in the topology. 

interface tunnel-te18
ipv4 unnumbered Loopback63
destination 33.33.33.33
path-selection
metric igp
!
path-option 1 segment-routing
path-option 2 dynamic segment-routing lockdown ospf Mark area 0

RP/0/RSP0/CPU0:Cisco-9K(config)#do show mpls traffic-eng tunnels
Tue Apr 18 11:28:47.131 UTC
Name: tunnel-te18 Destination: 33.33.33.33 Ifhandle:0x200e3a0
Signalled-Name: Cisco-9K_t18
Status:
Admin: up Oper: down Path: not valid Signalling: Down

path option 1, type segment-routing
Last PCALC Error: Tue Apr 18 11:24:05 2023
Info: Unable to find topolog node for 33.33.33.33
path option 2, (LOCKDOWN Segment-Routing) type dynamic
OSPF Mark area 0
Last PCALC Error: Tue Apr 18 11:26:34 2023
Info: Dynamic path-option with inter-area destination is not supported


The thing is that i have a SR-TE policy configured to see if this works and that policy is UP 

RP/0/RSP0/CPU0:Cisco-9K(config)#do show segment-routing traffic-eng policy tabular | inc 33.33.33.33
Tue Apr 18 11:29:33.751 UTC
1 33.33.33.33 up up 256023

Color: 1, End-point: 33.33.33.33
Name: srte_c_1_ep_33.33.33.33
Status:
Admin: up Operational: up for 00:22:18 (since Apr 18 11:07:43.671)
Candidate-paths:
Preference: 1 (configuration) (active)
Name: SRTE_bla
Requested BSID: dynamic
Protection Type: protected-preferred
Maximum SID Depth: 10
Explicit: segment-list sysp51 (valid)
Weight: 1, Metric Type: TE
16898
Attributes:
Binding SID: 256023
Forward Class: Not Configured
Steering labeled-services disabled: no
Steering BGP disabled: no
IPv6 caps enable: yes
Invalidation drop enabled: no

Ofcourse there is MPLS reachablity across the 3 routers.

I'm having a lot of difficulty understanding why i'm not seeing anything under the show segment-routing traffic-eng topology.
In addition regarding path 2 which was marked to search in the specific OSPF instance at the specific area. Why does it say that it is an INTRA-Area route when it is INTER-Area route.

Color: 1, End-point: 33.33.33.33
Name: srte_c_1_ep_33.33.33.33
Status:
Admin: up Operational: up for 00:22:18 (since Apr 18 11:07:43.671)
Candidate-paths:
Preference: 1 (configuration) (active)
Name: SRTE_bla
Requested BSID: dynamic
Protection Type: protected-preferred
Maximum SID Depth: 10
Explicit: segment-list sysp51 (valid)
Weight: 1, Metric Type: TE
16898
Attributes:
Binding SID: 256023
Forward Class: Not Configured
Steering labeled-services disabled: no
Steering BGP disabled: no
IPv6 caps enable: yes
Invalidation drop enabled: no


Thanks in advance! 
 

[Harold Ritter]

Hi @markk2316 ,

You need to configure "mpls traffic-eng" under the ospf process on all participating routers as follow:

router ospf Mark

area 0

mpls traffic-eng

Regards,

[markk2316]

Hey Harold, Thank you for the reply ! 
I have mpls traffic-eng configured under the router ospf.

router ospf Mark
router-id 66.110.0.63
segment-routing mpls
address-family ipv4 unicast
area 0
segment-routing forwarding mpls
mpls traffic-eng
segment-routing mpls
interface Loopback63
passive enable
prefix-sid index 63 explicit-null
!
interface Loopback99
passive enable
!
interface tunnel-te18
!
interface HundredGigE0/0/0/1.1370
network point-to-point
segment-routing forwarding mpls
!
!
mpls traffic-eng router-id Loopback63
!


In addition i am seeing that my route for 33.33.33.33 is resolved by labeled-sr (an entry exists under mpls forwarding as well) 

RP/0/RSP0/CPU0:Cisco-9K(config)#do show route 33.33.33.33
Wed Apr 19 06:48:28.693 UTC

Routing entry for 33.33.33.33/32
Known via "ospf Mark", distance 110, metric 2, labeled SR, type intra area
Installed Apr 19 06:38:02.945 for 00:10:26
Routing Descriptor Blocks
188.37.199.2, from 33.33.33.33, via HundredGigE0/0/0/1.1370
Route metric is 2
No advertising protos.

However the topology in the segment routing traffic engineering is empty. As if i'm missing a redistribute knob from ospf to segment routing. Can't pinpoint what exactly is missing.

OSPF database shows Type-10 Opaque Link Area Link States thus i've deemed the configuration of other devices to be stable.

Any chance you might know a scenario like this ? 

[MHM Cisco World]

Sorry I am Now so my answer can help you and can not, just want to mention this 
NOW 
you use Dynamic and I see you use same area in OSPF but the tunnel down reason show different 
""Dynamic path-option with inter-area destination is not supported""

so only make double check in three router the OSPF area.
thanks 

[markk2316]

Yes certainly all 3 routers are under the same area 
as shown in the OSPF database 

OSPF Router with ID (66.110.0.63) (Process ID Mark)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count
22.22.21.22 22.22.21.22 1688 0x80000013 0x00fe30 5
33.33.33.33 33.33.33.33 668 0x800001b8 0x009cd3 3
66.110.0.63 66.110.0.63 716 0x80000063 0x006bbe 4

Type-10 Opaque Link Area Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Opaque ID
1.0.0.0 66.110.0.63 234 0x8000005e 0x0012e2 0
1.0.0.1 33.33.33.33 68 0x8000000b 0x009c7f 1
1.0.3.220 66.110.0.63 716 0x8000000e 0x0016d7 988
4.0.0.0 22.22.21.22 1688 0x8000000f 0x008dd7 0
4.0.0.0 33.33.33.33 1271 0x80000058 0x002074 0
4.0.0.0 66.110.0.63 234 0x8000005f 0x003f3a 0
7.0.0.1 33.33.33.33 668 0x80000061 0x00fbb2 1
7.0.0.1 66.110.0.63 234 0x80000035 0x00e912 1
7.0.0.10 22.22.21.22 1688 0x8000000f 0x008aff 10
8.0.0.1 33.33.33.33 1690 0x8000000c 0x002ac3 1
8.0.0.26 22.22.21.22 1688 0x8000000f 0x00d59f 26
8.0.0.27 22.22.21.22 1688 0x8000000f 0x00c7f2 27
8.0.3.220 66.110.0.63 716 0x8000000e 0x00abee 988

[MHM Cisco World]

can I see the config of 33.33.33.33 router ?

[Harold Ritter]

Hi @markk2316 

The reason I suggested to configured "mpls traffic-eng" under ospf is that the legacy mpls traffic engineering database seemed to be empty. Can you do a "show mpls traffic-eng topo" and validate that it is not empty?

To fix the issue with the SR mpls traffic-engineering database being empty (sh segment-routing traffic-eng topology), you need to configure to configure "distribution link-state" under ospf.

router ospf Mark

distribute link-state

BTW, I would recommend that you move away from the legacy mpls traffic engineering configuration (int tunnel-te) and use a segment-routing policy instead, which is the new way of doing things.

Regards,

[markk2316]

Hey Harold !
I'd like to focus a bit on the segment-routing policy that you mentioned. 
I wanted to establish a Seamless-BFD session. According to the documentation i found 
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/seg_routing/configuration/xe-16-8/segrt-xe-16-8-book/sr-smlsbfd-sspf.pdf
Cisco supports s-BFD only on this specific SR-TE interface. 
I've established a policy and the policy was UP but there was no option to enable s-BFD on it.
Is there an option to run s-BFD without the need for the interface tunnel-te ?
Thanks in advance !

[Harold Ritter · Accepted solution]

Hi @markk2316 ,

The document you mention is for IOS XE. SBFD is supported for segment routing traffic engineering policies in IOS-XR, as stated in the following document:

https://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k-r7-4/segment-routing/configuration/guide/b-segment-routing-cg-asr9000-74x/configure-sr-te-policies.html#id_36805

Regards, 

[markk2316]

Thanks Harold that resolved my issue. 
I've managed to configure the Policy and it went UP  and with it sbfd packets began to flow. 
Thank you for the super fast reply. 

Pleasure !