RD on mpls

Answered Question
Apr 20th, 2007
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hi, does the rd(64bits) need to be propagated to remote PE? and which vpn label is used when PE router need to send to remote PE router? is the one that advertised from remote PE router or the vpn label generated by it self (origin PE router) ?

Correct Answer by mohammedmahmoud about 10 years 3 months ago

Hi there,


Thanks Andrea, Just to make the info complete, On the other PE routers that receive the VPNv4 route (IPv4+RD), the vpnv4 routes are stripped of the RDs and put into the VRF routing table as IPv4 routes (according to the RT).


HTH,

Mohammed Mahmoud.

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mohammedmahmoud Sat, 04/21/2007 - 01:09
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Hi there,


The combination of the RD with the IPv4 prefix of the customer provides a vpnv4 prefix, of which the address is 96 bits long. This 96-bit vpnv4 address is advertised between PEs via MBGP (while this RD has no significance on the other PEs but it is sent as a part of the VPNv4 address).


As for the second question, a customer data packet has two levels of labels (label stack) attached when it is forwarded across the backbone:


* the top label directs the packet to the correct egress PE router.

* the second label indicates how that PE router should forward the packet to the VPN interface.



HTH, please rate if it does,

Mohammed Mahmoud.

ariela Sat, 04/21/2007 - 01:16
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Hi,


"The route distinguisher has only one purpose: to make IPv4 prefixes globally unique. It is not used for routing by the provider's core (non-edge) routers (within the MPLS cloud), but it is used by the edge routers to identify which VPN a packet belongs to."


see that:

http://en.wikipedia.org/wiki/Route_distinguisher


HTH

Andrea

mohammedmahmoud Sat, 04/21/2007 - 01:23
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Hi there,


I just want to comment on the last feedback in order to avoid any misunderstanding.


The statement "it is used by the edge routers to identify which VPN a packet belongs to" is meant for the local PE router (for the sake of address overlapping between customers VPNs on the local PE only) not the other PE routers, all the other routers uses the RT (Route-target) as the VPN identifier.


HTH,

Mohammed Mahmoud.

ariela Sat, 04/21/2007 - 01:30
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yep, Mohammed is right.


RD is only a "local" tag, to prevent the IP overlapping.

Thanks for your comment.

Regards

Andrea

Correct Answer
mohammedmahmoud Sat, 04/21/2007 - 01:48
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Hi there,


Thanks Andrea, Just to make the info complete, On the other PE routers that receive the VPNv4 route (IPv4+RD), the vpnv4 routes are stripped of the RDs and put into the VRF routing table as IPv4 routes (according to the RT).


HTH,

Mohammed Mahmoud.

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