MPLS VPN With Cisco CSR and Cisco IOS-XR

[sachin30720041]

Hello All,

<------Site1-------><-----Site2---------->

R1----R2---R3---R4--XR5--R6---XR7---R8

R1, R2. R3, R4,R6, R7 are cisco CSR.

XR5, XR7 are cisco XR.

R1 and R8 are CE routers.

R2 and XR7 are PE routers.

ospf, ldp is running on r2,r3,r4 in site1.

ospf, ldp is running on xr5,r6,xr7 in site2.

100.100.100.100, 20.20.20.20 are loopbacks on R1(CE router site1) and R8(CE router site2).

192.168.255.2, 192.168.255.7 are loopbacks of R2 and XR7 respectively.

R4 and XR5 are running ipv4 bgp label. and exchange 192.168.255.2(loopback of R2) and 192.168.255.7(loopback of XR7) respectively.

R2 and XR7 are running BGP vpnv4.

Below is the configuration.

R2

vrf definition A

rd 192.168.255.2:65000

!

address-family ipv4

route-target export 99:99

route-target import 99:99

exit-address-family

!

interface Loopback1

ip address 192.168.255.2 255.255.255.255

ip ospf 1 area 0

!

interface gig2

no sh

vrf forwarding A

ip address 192.168.12.2 255.255.255.0

ip ospf 10 area 0

interface gig1

no sh

ip address 192.168.23.2 255.255.255.0

ip ospf 1 area 0

mpls ip

!

router ospf 10 vrf vrf1

redistribute bgp 65000 subnets

router ospf 1

!

router bgp 65000

bgp log-neighbor-changes

no bgp default ipv4-unicast

neighbor 192.168.255.7 remote-as 65001

neighbor 192.168.255.7 update-source Loopback1

neighbor 192.168.255.7 ebgp-multihop

address-family ipv4

exit-address-family

!

address-family vpnv4

neighbor 192.168.255.7 activate

neighbor 192.168.255.7 send-community both

exit-address-family

!

address-family ipv4 vrf A

redistribute ospf 10

exit-address-family

-----------------------------------

R4

interface Loopback1

ip address 192.168.255.4 255.255.255.255

ip ospf 1 area 0

!

interface gig2

no sh

ip address 192.168.34.4 255.255.255.0

ip ospf 1 area 0

mpls ip

!

interface gig1

no sh

ip address 192.168.45.4 255.255.255.0

mpls bgp forwarding

!

router ospf 1

redistribute bgp 65000 subnets route-map REDISTRIBUTE_IN_IGP

!

router bgp 65000

bgp log-neighbor-changes

network 192.168.255.2 mask 255.255.255.255

neighbor 192.168.45.5 remote-as 65001

address-family ipv4 unicast

neighbor 192.168.45.5 activate

neighbor 192.168.45.5 send-label

!

ip prefix-list FOREIGN_PREFIXES seq 10 permit 192.168.255.7/32

!

route-map REDISTRIBUTE_IN_IGP permit 10

match ip address prefix-list FOREIGN_PREFIXES

!

--------------------------------------------

R5

interface Loopback1

ipv4 address 192.168.255.5 255.255.255.255

!

interface GigabitEthernet0/0/0/1

no sh

ipv4 address 192.168.45.5 255.255.255.0

!

interface GigabitEthernet0/0/0/0

no sh

ipv4 address 192.168.56.5 255.255.255.0

!

prefix-set FOREIGN_PREFIXES

192.168.255.2/32,

192.168.255.3/32

end-set

!

route-policy DEFAULT

pass

end-policy

!

route-policy REDISTRIBUTE_IN_IGP

if destination in FOREIGN_PREFIXES then

pass

endif

end-policy

!

router static

address-family ipv4 unicast

192.168.45.4/32 GigabitEthernet0/0/0/1

!

router ospf 1

address-family ipv4 unicast

router-id 192.168.255.5

redistribute bgp 65001 route-policy REDISTRIBUTE_IN_IGP

area 0

interface Loopback1

!

interface GigabitEthernet0/0/0/0

!

router bgp 65001

address-family ipv4 unicast

network 192.168.255.7/32

allocate-label all

!

neighbor 192.168.45.4

remote-as 65000

address-family ipv4 labeled-unicast

route-policy DEFAULT in

route-policy DEFAULT out

!

mpls ldp

address-family ipv4

!

interface GigabitEthernet0/0/0/0

!

---------------------------------

R7

route-policy pass

pass

exit

vrf A

address-family ipv4 unicast

import route-target

99:99

!

export route-target

99:99

!

!

interface Loopback1

ipv4 address 192.168.255.7 255.255.255.255

!

interface GigabitEthernet0/0/0/1

no vrf vrf1

ipv4 address 192.168.67.7 255.255.255.0

no sh

!

interface GigabitEthernet0/0/0/0

vrf A

ipv4 address 192.168.78.7 255.255.255.0

no sh

!

router ospf 1

address-family ipv4

area 0

interface Loopback1

!

interface GigabitEthernet0/0/0/1

vrf A

redistribute bgp 65001

area 0

int gi0/0/0/0

!

router bgp 65001

address-family vpnv4 unicast

!

neighbor 192.168.255.2

remote-as 65000

update-source Loopback1

ebgp-multihop

address-family vpnv4 unicast

route-policy pass in

route-policy pass out

!

vrf A

rd 192.168.255.12:65001

address-family ipv4 unicast

redistribute ospf 1

!

mpls ldp

address-family ipv4

!

interface GigabitEthernet0/0/0/1

I see 100.100.100.100/32(R1's loopback) in R8's routing table and 20.20.20.20(R8's loopback) in R1's routing table. Routes between R1 and R8 are getting exchanged. But ping is not working from R1 to R8.  XR7 has the following labels.

RP/0/RP0/CPU0:XR7 # show mpls forwarding

incoming.   outgoing.    Prefix.                         interface.      nexthop

label            label

24002         Pop            192.168.255.2/32    Gi0/0/0/1    192.168.67.6

For prefix 192.168.255.2(R2's loopback),  XR7 is poping the label.

On R2 I see label 19 as an outgoing label for 192.168.255.7(XR7's loopback).

R2#show mpls forwarding-table
20   19    192.168.255.7/32 0     Gi1   192.168.23.3

That's why the ping request from R1 reaches R8 but the reply is dropped by XR7.

Do I need to do extra configuration on XR7? 

Thanks,

Sachin

[Harold Ritter · Accepted solution]

Hi @sachin30720041 ,

The issue is that when you configure an ebgp session, XR does not allow the session to be established over an LSP by default. It does that by installing a pop label operation locally for the neighbor address. You can change that default behavior by adding the mpls keyword to the "ebgp-multihop" command as follow:

XR7:

router bgp 65001

neighbor 192.168.255.2

remote-as 65000

update-source Loopback1

ebgp-multihop mpls

This should fix the issue you are seeing.

Regards,

[sachin30720041]

Thank you so much, Harold!!!