Re: 3 MPLS labels at RFC 4364 - Page 2

study_voip · ‎09-17-2007

Hello,

shown on 33 page of RFC4364, for inter-AS Mpls VPN, if the /32 host routes are unknown by the ASes, it need 3 labels, who can give an example to explain how the 3 labels works.

thanks in advance

If the /32 routes for the PE routers are made known to the P

routers of each AS, everything works normally. If the /32

routes for the PE routers are NOT made known to the P routers

(other than the ASBRs), then this procedure requires a packet's

ingress PE to put a three-label stack on it. The bottom label

is assigned by the egress PE, corresponding to the packet's

destination address in a particular VRF. The middle label is

assigned by the ASBR, corresponding to the /32 route to the

egress PE. The top label is assigned by the ingress PE's IGP

Next Hop, corresponding to the /32 route to the ASBR.

swaroop.potdar · ‎09-21-2007

You dont need to do the set mpls label.

And you will not find the labels assigned when you use the "show mpls forwarding".

Use the command "show ip bgp labels" to see the route and the labels in AS1 assigned by BGP received from the AS2 on your PE1_AS1.

You should have 3 label stack easily simulated if you simply follow the steps as below.

1) configure each AS properly to function as a single AS MPLS VPN.

2) At each ASBR redistribute the IGP (loopback) routes into BGP.

3) At both the ASBR's mention send label towards each other.

4) At both ASBR's have a IBGP session with send label to the PE's in their own AS.

5) form a multihop VPNV4 MPBGP session between the PE's in both AS's( for eg PE1_AS1 <-Multihop MPEBGP-> PE1_AS2.

Thats all about it. If you have the VRF configured and exchanged using the RT;s at both ends and follow the steps above you will have a 3 label stack.

HTH-Cheers,

Swaroop

study_voip · ‎09-21-2007

ohoo

sh ip cef vrf a 1.1.1.1

1.1.1.1/32, version 13, epoch 0, cached adjacency to Serial3/3

0 packets, 0 bytes

tag information set

local tag: VPN-route-head

fast tag rewrite with Se3/3, point2point, tags imposed: {501 807 604}

via 6.6.6.6, 0 dependencies, recursive

next hop 89.89.89.88, Serial3/3 via 6.6.6.6/32

valid cached adjacency

tag rewrite with Se3/3, point2point, tags imposed: {501 807 604}

sh ip cef vrf a 5.5.5.5

5.5.5.5/32, version 12, epoch 0, cached adjacency 67.67.67.7

0 packets, 0 bytes

tag information set

local tag: VPN-route-head

fast tag rewrite with Fa0/0, 67.67.67.7, tags imposed: {701 207 904}

via 9.9.9.9, 0 dependencies, recursive

next hop 67.67.67.7, FastEthernet0/0 via 9.9.9.9/32

valid cached adjacency

tag rewrite with Fa0/0, 67.67.67.7, tags imposed: {701 207 904}

sh ip bgp labels

Network Next Hop In Label/Out Label

2.2.2.2/32 2.2.2.2 600/imp-null

6.6.6.6/32 0.0.0.0 imp-null/nolabel

8.8.8.8/32 2.2.2.2 nolabel/206

9.9.9.9/32 2.2.2.2 nolabel/207

router bgp 1

no bgp default ipv4-unicast

bgp log-neighbor-changes

neighbor 2.2.2.2 remote-as 1

neighbor 2.2.2.2 update-source Loopback0

neighbor 9.9.9.9 remote-as 2

neighbor 9.9.9.9 ebgp-multihop 255

neighbor 9.9.9.9 update-source Loopback0

!

address-family ipv4

neighbor 2.2.2.2 activate

neighbor 2.2.2.2 next-hop-self

neighbor 2.2.2.2 send-label

no auto-summary

no synchronization

network 6.6.6.6 mask 255.255.255.255

exit-address-family

!

address-family vpnv4

neighbor 2.2.2.2 activate

neighbor 2.2.2.2 send-community extended

neighbor 9.9.9.9 activate

neighbor 9.9.9.9 send-community extended

exit-address-family

now i need to understand it along the LSP, i think the tricky part is i need send-label between the ASBR1 and PE1 in AS#1 and same with AS2

thanks a lot, your way works.