From: Tarun Pahuja (pahujat@gmail.com)
Date: Mon Dec 03 2007 - 06:14:20 ART
Ali,
Few things to remember:
1) In an MPLS Core, the Core routers(LSRs) forward packets based on Tags.
These tags are distributed as soon as you enable tag-switching on core
routers.
2) MPLS VPN uses the concept of VRF's. Every Customer is uniquely identified
using a different RD(Route Distinguisher) Value.
3) The PE Routers talk to each other using MP-BGP.Multi-protocol BGP is an
extension of BGP which can carry extended communities like route-targets,
VPNV4 prefix's required for MPLS VPNs.
4) In MPLS VPNs, there are 2 tags involved. The inner tag is the VPN tag and
the outer most tag is the LDP tag used for reaching the next hop router
which is the remote (PE).
5) When a Packet arrives from a customer's CE router , The PE looks at the
VRF table and checks to see what the next hop is.The next hop would be the
IP Address of the remote PE where the corresponding vrf exists carring the
destination network for the packet in it's vrf table.
6) Tag-switching within the core takes the responsibility of delivering this
packet from the source PE to the destination PE.
HTH,
Tarun
On 12/3/07, Ali.Huang <zero5291@gmail.com> wrote:
>
> hi,guys,
> I met a confusing question when I study mpls.When one PE receives a
> packet,it will check the destation,and find the match entry which gets
> from iBGP neighbor.
> The PE will import label before forward the P routers.I want to know
> whether the PE forwards the packet based on the label of next-hop,iBGP
> neighbor.I didn't get any information from my materials.So I want to
> confirm this.
> --
> THX.
> Ali.huang
>
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