Segment routing's anycast sid on XRV9k and XE

[sachin30720041]

Hello,

I have the following setup. And  I have configured anycast sid on CSR2 and XR3. I have configured a policy in XRV4 with endpoint 1.1.1.1.

                    CSR2

                 /             \

           /                      \

CSR1                       XRV4

        \                       /

           \               /

               XR3

1.1.1.1 is loopback on CSR1. And I have included 'anycast-sid-inclusion' command in the policy.

segment-routing
traffic-eng
policy pol1
source-address ipv4 4.4.4.4
color 123 end-point ipv4 1.1.1.1
candidate-paths
preference 100
dynamic
anycast-sid-inclusion
exit

But I do not see anycast sid in the path of policy pol1.

Below is the output of 'show segment-routing traffic-eng policy name srte_c_123_ep_1.1.1.1'.

XRV4#show segment-routing traffic-eng policy name srte_c_123_ep_1.1.1.1

SR-TE policy database
---------------------

Color: 123, End-point: 1.1.1.1
Name: srte_c_123_ep_1.1.1.1
Status:
Admin: up Operational: up for 00:31:35 (since Jul 27 00:0 7:26.625)
Candidate-paths:
Preference: 100 (configuration) (active)
Name: pol1
Requested BSID: dynamic
Maximum SID Depth: 10
Anycast Inclusion: Enabled
Dynamic (valid)
Metric Type: TE, Path Accumulated Metric: 20
24005 [Adjacency-SID, 100.20.40.4 - 100.20.40.2]
16001 [Prefix-SID, 1.1.1.1]

What is the equivalent of 'anycast-sid-inclusion' on Cisco CSR router ?

CSR1
----------------
segment-routing mpls
connected-prefix-sid-map
address-family ipv4
1.1.1.1/32 index 1 range 1
exit
int gi1
ip address 100.10.20.1 255.255.255.0
ip router isis 1
isis network point-to-point
no sh

int gi2
ip address 100.10.30.1 255.255.255.0
ip router isis 1
isis network point-to-point
no sh

int lo0
ip address 1.1.1.1 255.255.255.255
ip router isis 1
exit

router isis 1
is-type level-1
net 49.0001.1111.1111.1111.00
router-id lo0
metric-style wide
distribute link-state
segment-routing mpls
mpls traffic-eng router-id lo0
mpls traffic-eng level-1
exit

CSR2
-----------------------
segment-routing mpls
connected-prefix-sid-map
address-family ipv4
2.2.2.2/32 index 2 range 1
23.23.23.23/32 index 23 range 1
exit

int gi1
ip address 100.10.20.2 255.255.255.0
ip router isis 1
isis network point-to-point
no sh

int gi2
ip address 100.20.40.2 255.255.255.0
ip router isis 1
isis network point-to-point
no sh

int lo0
ip address 2.2.2.2 255.255.255.255
exit

int lo1
ip address 23.23.23.23 255.255.255.255
ip router isis 1
isis prefix n-flag-clear
exit

router isis 1
is-type level-1
net 49.0001.2222.2222.2222.00
router-id lo0
metric-style wide
distribute link-state
segment-routing mpls
mpls traffic-eng router-id lo0
mpls traffic-eng level-1
exit

XR3
-----------------------
int gi0/0/0/0
ip address 100.30.40.3 255.255.255.0
no sh

int gi0/0/0/2
ip address 100.10.30.3 255.255.255.0
no sh

int lo0
ip address 3.3.3.3 255.255.255.255
exit

int lo1
ip address 23.23.23.23 255.255.255.255
exit

router isis 1
is-type level-1
net 49.0001.3333.3333.3333.00
distribute link-state
address-family ipv4 unicast
metric-style wide
router-id lo0
segment-routing mpls
mpls traffic-eng router-id lo0
mpls traffic-eng level-1
exit
int gi0/0/0/0
point-to-point
address-family ipv4 unicast
exit
int gi0/0/0/2
point-to-point
address-family ipv4 unicast
exit
int lo1
address-family ipv4 unicast
prefix-sid index 23
exit

XR4
-----------------------
segment-routing
traffic-eng
policy pol1
source-address ipv4 4.4.4.4
color 123 end-point ipv4 1.1.1.1
candidate-paths
preference 100
dynamic
anycast-sid-inclusion
exit
root

int gi0/0/0/0
ip address 100.30.40.4 255.255.255.0
no sh

int gi0/0/0/2
ip address 100.20.40.4 255.255.255.0
no sh

int lo0
ip address 4.4.4.4 255.255.255.255
exit

router isis 1
is-type level-1
net 49.0001.4444.4444.4444.00
distribute link-state
address-family ipv4 unicast
metric-style wide
router-id lo0
segment-routing mpls
mpls traffic-eng router-id lo0
mpls traffic-eng level-1
exit
int gi0/0/0/0
point-to-point
address-family ipv4 unicast
exit
int gi0/0/0/2
point-to-point
address-family ipv4 unicast
exit
int lo0
address-family ipv4 unicast
prefix-sid index 4
exit

Thanks,

Sachin

[Harold Ritter · Accepted solution]

Hi @sachin30720041 ,

The anycast config is incomplete on CSR2 and XRV3. You nee to advertised the prefix-sid for the  lo0 interface and additionally the anycast prefix-sid with the n flag cleared for lo1 (anycast loopback interface).

On CSR2, you are missing the following:

int lo0

ip router isis 1

On XRV3, you are missing the following:

router isis 1

int lo0
address-family ipv4 unicast
prefix-sid index 3 

Int lo1
address-family ipv4 unicast
prefix-sid index 23 n-flag-clear

Regards,

[sachin30720041]

Hello Harold,

Thanks for the reply.

I made the changes but when I ping from XR4 to CSR1 I see only MPLS LABEL 16001 in the packet. I do not see 16023 in the packet. If anycast is working correctly then there should 16023 and 16001 in the packet. Correct ?

RP/0/RP0/CPU0:XR4#traceroute 1.1.1.1 source 4.4.4.4
Wed Jul 27 19:04:55.760 UTC

Type escape sequence to abort.
Tracing the route to 1.1.1.1

1 100.20.40.2 [MPLS: Label 16001 Exp 0] 57 msec 9 msec 8 msec
2 100.10.30.1 55 msec
100.10.20.1 45 msec *

[Harold Ritter · Accepted solution]

Hi @sachin30720041 ,

This is normal behavior, given that XRV4 is directly connected to both XRV3 and CSR2, which explains why this anycast sid is not being used, just the same as the node sid would not be used in tis context. 

Regards, 

[Harold Ritter · Accepted solution]

Hi @sachin30720041 ,

Also, bear in mind that traffic to 1.1.1.1 would not be forwarded using the policy by default. You would need to use "autoroute" under the policy to make sure traffic to 1.1.1.1 is steered through the policy.

segment-routing
traffic-eng
policy pol1
autoroute
include ipv4 1.1.1.1/32
!

Regards,

[sachin30720041]

What is the equivalent of 'anycast-sid-inclusion' on Cisco CSR router ?

Thanks,

Sachin

[Harold Ritter · Accepted solution]

Hi @sachin30720041 ,

This is currently not supported on the CSR1k. It is on the roadmap though.

Regards,