mpls bgp forwarding

[Hari Vishnu]

Hi All,

Can anyone please explain the use of "mpls bgp forwarding". I understand that its used in Option 2 Inter AS VPN.

Ta

[Nagendra Kumar Nainar · Accepted solution]

Hi,

A node should understand if it can send/accept labeled packet over any interafce. When LDP is used as label distribution protocol, enabling "mpls ip" will not only enable LDP (Control plane), but also allows the LSR to send/accept labeled packet over the interface. In case of Inter-AS Option B, BGP is used as label distribution protocol between ASBRs. So the command "mpls bgp forwarding" enables ASBR to send/accept labeled packet over the configured interface (whcih is towards the other ASBR).

-Nagendra

[sachin30720041]

Hi Nagendra,

That means in case of bgp+label, We should always enable 'mpls bgp forwarding' on the interfaces ?

[Harold Ritter]

Hi @sachin30720041 ,

This is only required for eBGP sessions.

Regards,

[mohameedsabry4]

Hi harold,

what is the equivalent command for it on IOS-XR on 9K routers.

interface Port-channel1

 mpls bgp forwarding

[Harold Ritter]

Hi @mohameedsabry4 ,

I suppose it is for an interAS option B or C scenario? With XR, you would need to configure a static route to the eBGP neighbor as follow:

router static 

address-family ipv4 unicast

<ebgp neighbor address>/32 <interface to the ebgp neighbor>

For more information, please refer to the following document:

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

Regards,

[mohameedsabry4]

Hi harold,

Thanks for your effort, excuse me as i still have below inquires about establishing INTER-AS MPLS VPN Option B (on P2P IPs).

i am controlling 1 side configuration on IOS router and need to replace it with XR router (9006 with S/W version 7.1.3).

below configuration is related to the configuration between the 2 ASBR for AS65000 and AS36555 only.

IOS (Current applied configuration)

XR  (The configuration that will be applied and need to confirm it )

interface Gi0/0/0 mtu 9216 ip address 1.1.1.1 255.255.255.252 negotiation auto mpls ip mpls mtu 1540 mpls bgp forwarding ! router bgp 65000 no bgp default ipv4-unicast no bgp default route-target filter neighbor 1.1.1.2 remote-as 36555 neighbor 1.1.1.2 update-source Gi0/0/0 ! address-family vpnv4   neighbor 1.1.1.2 activate   neighbor 1.1.1.2 send-community both   neighbor 1.1.1.2 route-map Test-IN in   neighbor 1.1.1.2 route-map Test-OUT out ! address-family ipv4 mdt   neighbor 1.1.1.2 activate   neighbor 1.1.1.2 send-community extended

interface Gi0/0/0/8 no shut mtu 9216 ip address 1.1.1.1 255.255.255.252 mpls   mtu 1540 ! router static address-family ipv4 unicast 1.1.1.2/32 Gi0/0/0/8 exit ! router bgp 65100 address-family ipv4 unicast allocate-label all ! address-family vpnv4 unicast   retain route-target all ! neighbor 1.1.1.2   remote-as 36555   update-source Gi0/0/0/8   address-family vpnv4 unicast    route-policy Test-IN in    route-policy Test-OUT out    !   address-family ipv4 mdt    send-extended-community-ebgp    !

1. Static route considered to replace “mpls bgp forwarding”.
2. Do i need to use "allocate-label all" under address-family IPV4 in option B on XR.
3. Send-community both is not found under address family VPNV4 under the ebgp neighbor on XR.

please advise, Thanks you.

[Harold Ritter]

Hi @mohameedsabry4 ,

1. Correct

2. This would be needed for an InterAS option C scenario. It is not needed for option B.

3. This is done by default for VPNv4 AF.

Regards, 

[mohameedsabry4]

Thanks a lot for your above reply, really is very useful.

- should "no bgp default route-target filter" on IOS be replaced with "retain route-target all" under Vpnv4 address-family? for XR.

- Does the link between 2 ASes in option B configure without or with MPLS as below.

mpls ldp
  interface GigabitEthernet0/0/0/8

if without, this will mean that the static route will be enough as even if we configure MPLS on this link the implicit null will execute the traffic without MPLS tag.

[Harold Ritter]

Hi @mohameedsabry4 ,

You are very welcome.

> - should "no bgp default route-target filter" on IOS be replaced with "retain route-target all" under > Vpnv4 address-family? for XR.

This is correct.

> - Does the link between 2 ASes in option B configure without or with MPLS as below.

This is not needed, as you do not want LDP to be enabled on the link between the two ASes. With the static route configured, you will see this link when you do a "show mpls interfaces".

Regards,

[mohameedsabry4]

Hello Harold,

Thank you very much for the effort, You made my day.

[Harold Ritter]

You are very welcome @mohameedsabry4 and thanks for the feedback. Do not hesitate to let us if you have any additional questions