CSC, MPLS, and EBGP LU routing failure

[tomc.pnnl]

Good day,

I'm configuring CSC using EBGP labeled unicast and having problem with the CEs resolving routes. The minimal working example is:

192.168.1.1/32                                                                                                                 192.168.1.2/32

|                                                                                                                                        |

loop0                                                                                                                                loop0

|                                                                                                                                        |

CE1 192.168.1.1/30 -- 192.168.1.2/30 PE1 -- PE2 192.168.1.6/30 -- 192.168.1.5/30 CE2

CE1's global routing table appears to be correct:

L 127.0.0.0/8 [0/0] via 0.0.0.0, 01:22:49
L 192.168.1.1/32 is directly connected, 01:22:40, Loopback0
B 192.168.1.2/32 [20/0] via 192.168.128.1, 00:17:52
C 192.168.128.0/30 is directly connected, 01:22:40, GigabitEthernet0/0/0/1
L 192.168.128.2/32 is directly connected, 01:22:40, GigabitEthernet0/0/0/1

When I trace ipv4 192.168.1.2 source 192.168.1.1

1 192.168.128.2 !N * !N

I run into a local problem (192.168.128.2 is the address of CE1 interface)

Can I anyone shed some light? Configurations for CE1 and PE2 follow:

CE1

interface Loopback0
ipv4 address 192.168.1.1 255.255.255.255
!
interface GigabitEthernet0/0/0/0
shutdown
!
interface GigabitEthernet0/0/0/1
description PE1
mtu 6144
ipv4 address 192.168.128.2 255.255.255.252
!

route-policy ACCEPT_ALL
pass
end-policy
!
router bgp 100
bgp router-id 192.168.1.1
bgp log neighbor changes detail
address-family ipv4 unicast
network 192.168.1.1/32
allocate-label all
!
neighbor 192.168.128.1
remote-as 1
address-family ipv4 labeled-unicast
route-policy ACCEPT_ALL in
route-policy ACCEPT_ALL out
!
!
mpls oam
!

sh route

L 127.0.0.0/8 [0/0] via 0.0.0.0, 01:35:25
L 192.168.1.1/32 is directly connected, 01:35:16, Loopback0
B 192.168.1.2/32 [20/0] via 192.168.128.1, 00:30:28
C 192.168.128.0/30 is directly connected, 01:35:16, GigabitEthernet0/0/0/1
L 192.168.128.2/32 is directly connected, 01:35:16, GigabitEthernet0/0/0/1

sh mpls forwarding
Wed Mar 24 18:50:22.630 UTC
Local Outgoing Prefix Outgoing Next Hop Bytes
Label Label or ID Interface Switched
------ ----------- ------------------ ------------ --------------- ------------
24000 Aggregate 192.168.128.0/30 default 0
24001 Pop 192.168.128.2/32 192.168.128.2 0
24002 24004 192.168.1.2/32 192.168.128.1 0

PE

vrf vpnA
address-family ipv4 unicast
import route-target
100:0
!
export route-target
100:0
!
!
!

interface Loopback0
ipv4 address 192.168.255.1 255.255.255.255
!
interface GigabitEthernet0/0/0/0
description PE2
mtu 6144
ipv4 point-to-point
ipv4 unnumbered Loopback0
!
interface GigabitEthernet0/0/0/1
description CE1
mtu 6144
vrf vpnA
ipv4 address 192.168.128.1 255.255.255.252
!

route-policy ACCEPT_ALL
pass
end-policy
!
router isis 1
net 49.0001.1921.6825.5001.00
lsp-password hmac-md5 encrypted 073F007F7D3E363733
address-family ipv4 unicast
metric-style wide
mpls traffic-eng level-1
mpls traffic-eng router-id Loopback0
segment-routing mpls
!
interface Loopback0
passive
address-family ipv4 unicast
prefix-sid index 101
!
!

interface GigabitEthernet0/0/0/0
suppressed
circuit-type level-1
point-to-point
address-family ipv4 unicast
!
!

!

router bgp 1
bgp router-id 192.168.255.1
bgp log neighbor changes detail
address-family vpnv4 unicast
!
neighbor 192.168.255.2
remote-as 1
address-family vpnv4 unicast
!
!
vrf vpnA
rd auto
address-family ipv4 unicast
allocate-label all
!
neighbor 192.168.128.2
remote-as 100
update-source GigabitEthernet0/0/0/1
address-family ipv4 labeled-unicast
route-policy ACCEPT_ALL in
route-policy ACCEPT_ALL out
as-override
!
!
!
!
mpls oam
!
mpls traffic-eng
!
segment-routing

sh route vrf vpnA

...

B 192.168.1.1/32 [20/0] via 192.168.128.2, 01:30:24
B 192.168.1.2/32 [200/0] via 192.168.255.2 (nexthop in vrf default), 00:29:27
C 192.168.128.0/30 is directly connected, 01:34:23, GigabitEthernet0/0/0/1
L 192.168.128.1/32 is directly connected, 01:34:23, GigabitEthernet0/0/0/1

[MHM Cisco World]

between CE and PE there is eBGP?
so why the neighbor and remote as is different?

[tomc.pnnl]

I've corrected the post to reflect the correct ASN. It was error introduced when writing the post.

[MHM Cisco World]

please note that the MPLS TE is unidirectional so in other side are you config also MPLS TE or not?

[Harold Ritter · Accepted solution]

Hi,

There are a few elements missing.

1. IOS-XR requires a static routes between 2 eBGP LU neighbors as discussed in the following document:

https://www.cisco.com/c/en/us/support/docs/multiprotocol-label-switching-mpls/mpls/200523-Configuration-and-Verification-of-Layer.html

"For Cisco IOS-XR over Inter-AS link, there is a different logic as compared to that of Cisco IOS. It is required to configure a static /32 route to ASBR1's interface, so that MPLS label is bound for a /32 prefix. If this is not done then the control plane will come up, but the traffic will not be forwarded."

on CE1:

router static
address-family ipv4 unicast
192.168.128.1/32 GigabitEthernet0/0/0/0
 on PE1:

router static
vrf vpnA
address-family ipv4 unicast
192.168.128.2/32 GigabitEthernet0/0/0/0

Make sure you replicate between PE2 and CE2 as well. 

2. You need to configure the update-source for the iBGP session between PE1 and PE2.

on PE1:

neighbor 192.168.255.2
remote-as 1
update-source Loopback0
address-family vpnv4 unicast
!

on PE2:

neighbor 192.168.255.1
remote-as 1
update-source Loopback0
address-family vpnv4 unicast
!

Regards,

[tomc.pnnl]

Thank you!