Re: MPLS L3 VPN Questions

Thanks Brian,

      Just got thru VOL I MPLS section, I had to re-read and go over a
couple of times and also watch ATC VOD and Marko's Video, But I understand
it now.

Thanks everyone on this list.

On Fri, Jun 3, 2011 at 2:47 PM, Brian McGahan <bmcgahan_at_ine.com> wrote:

> It's confusing because they use the same format, but in reality they are
> two completely unrelated attributes. The simplest explanation is that the
> Route Distinguisher (RD) makes the route unique, and the Route Target (RT)
> controls the VPN membership.
>
> The reason you need the RD is that multiple customers can have the same
> IPv4 route, but should not have the same VPNv4 route. For example if two
> separate customers both advertise the IPv4 prefix 10.0.0.0/24 to the
> Service Provider, the SP needs to tell the difference between them in the
> BGP table. To accomplish this, the prefixes get separate RD values appended
> onto them, making unique VPNv4 routes. E.g. if the RDs are 1:1 and 2:2, the
> VPNv4 routes are 1:1:10.0.0.0/24 and 2:2:10.0.0.0/24, which means they are
> treated as unrelated routes in the BGP bestpath selection process.
>
> The reason you need the RT is that the VRF membership assignment is only
> locally significant. The RT is basically a tag value that tells the remote
> PEs what VRFs a route is supposed to belong to. Additionally decoupling the
> RT from the RD allows the SP to form complex topologies, such as
> hub-and-spoke or central services VPNs in addition to full mesh. The
> "export" route target controls the tag as the route leaves the VRF and goes
> into BGP. The "import" route target controls what routes enter the VRF from
> BGP on the other side.
>
> HTH,
>
>
> Brian McGahan, CCIE #8593 (R&S/SP/Security)
> bmcgahan_at_INE.com
>
> Internetwork Expert, Inc.
> http://www.INE.com
> ________________________________________
> From: nobody_at_groupstudy.com [nobody_at_groupstudy.com] On Behalf Of Elliott
> Reyes [fontananetworkengineer_at_gmail.com]
> Sent: Friday, June 03, 2011 12:01 PM
> To: Cisco certification
> Subject: MPLS L3 VPN Questions
>
> Hey Guys,
>
> I'm just trying to get a better understanding of how to build these
> MPLS VPN's properly and I guess the documentation and INE workbook just
> confuses me a little bit. So if anyone can assist me that would be great.
>
>
> Like Denzel in the movie Philadelphia. Explain it to me like I'm a 6 year
> old.
>
> 1. When defining the VRF's between two PE routers.
>
>
> Example
>
> R1
>
> Step 1 - Create VRF locally on R1
>
> ip vrf VPN_A
>
> rd 100:1 <---- ROUTE DISTINGUISHER (This is locally significant to R1 and
> add's a 8 byte value to IPV4 prefix to create a VPNIPV4 prefix. )
>
>
> Step 2 - Assign Route-Target command
> route-target both 100:1 <----- allows routing information from to traverse
> from R1 VPN_A to R2 VPN_A thru their connected interfaces and import/export
> routing information.
>
> R1 <----------> R2
>
> int fa0/1 (R1)
> ip vrf forwarding VPN_A
> ip add 10.1.1.1 255.255.255.0
>
>
> R2
>
> Step 1 - Create VRF locally on R2
>
> ip vrf VPN_A
>
> rd 100:1 <---- ROUTE DISTINGUISHER (This is locally significant to R2 and
> add's a 8 byte value to IPV4 prefix to create a VPNIPV4 prefix. )
>
>
> Step 2 - Assign Route-Target command
> route-target both 100:1 <----- allows routing information from to traverse
> from R2 VPN_A to R1 VPN_A thru their connected interfaces and import/export
> routing information.
>
> Question - Does the route-target have to match the route distinguisher on
> both ends. if the route-target is say 100:2 and the route distinguisher is
> 100:1 on VPN_A this technically shouldn't work
> across the VPN correct.
>
> R2 <----------> R1
>
> int fa0/1 (R2)
> ip vrf forwarding VPN_A
> ip add 10.1.1.2 255.255.255.0
>
>
> thanks
>
>
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Received on Fri Jun 03 2011 - 15:21:56 ART