The MPLS-OPS Archive

[dwk@danakonkin.com]

Many thanks Martin,


If I may take this a step further...



Would the following summary be correct and adequate to describe the
funnction of RT and RD ?

1)
RD is necessary to create a globally unique address on the PE (VPN-IPv4 ie.
xxx:yy:a.b.c.d) from an IPv4 address learned from the CE. However the
config...

PE2(config)#ip vrf HOSTNAME 
PE2(config-vrf)#rd 100:27 



2)
...will not result in any prefixes that exist in vrf HOSTNAME on PE2 being
announced by MP-BGP. For that to occur, we need to add the following config.

PE2(config-vrf)#route-target export nn:mm (pick your numbers for the
variables)



3)
Further, no MP-BGP learned VPN-IPv4 prefixes will be installed into vrf
HOSTNAME unless you add the command:

PE2(config-vrf)#route-target import ff:gg (again, pick your numbers for the
variables)


(AND of course ff:gg matches the extended community attribute on a MP-BGP
learned VPN-IPv4 prefix !)




btw-Could anyone elaborate on the merits/demerits of having the value for RD
= RT ?

ie.
PE2(config)#ip vrf HOSTNAME 
PE2(config-vrf)#rd 100:27 
PE2(config-vrf)#route-target export 100:27
PE2(config-vrf)#route-target import 100:27



I wish to extend my appreciation to all for this forum. I can only state
that no matter how well a book may be written, it is a great help to have
peolpe to bounce back and forth with on some topics.


thanks,
Dana 

-----Original Message-----
From: Martin Heusinger
To: dwk@danakonkin.com; mpls-ops@mplsrc.com
Sent: 18/02/03 13:58
Subject: Re: [MPLS-OPS]: Route Distinguisher Questions

Hi Dana,

see my comments inline.

Cheers

Martin

On Tue, 18 Feb 2003 08:09:27 -0500, <dwk@danakonkin.com> wrote:

> Apologies, for after reading the last few weeks of this list I am
still
> unclear on the RD/RT issue, so I hope you do not mind if I ask another
> question.
>
>
> The config:
>
> PE2(config)#ip vrf HOSTNAME PE2(config-vrf)#rd 100:27 PE2(config-vrf) 
> #route-target import 2:2
>
> My humble understanding is this will result in the creation of a vrf
on 
> PE2
> (assuming there exists appropriate BGP address-family config) of 
> 'HOSTNAME'
> and the prefixes will be 'converted' to VPN-IPv4 by prepending the RD 
> 100:27
> onto the IPv4 prefix.
> Additionally, any prefixes carried by MP-BGP to PE2 with the Extended
> Community attribute as 2:2 will be installed into the 'HOSTNAME' vrf
on 
> PE2
> as routes. (please tell me if I am wrong)

This is quite right! One question: Where do you think these routes with
2:2 
would come from? Or more specific: How are these VPNv4 prefixes "marked"

with the extended BGP community 2:2?

>
>
> PE2(config-vrf)#route-target export 2:2
>
> Hmmm, I am not sure about this. 1. What purpose does this serve if
those 
> VPN-IPv4 prefixes already are being
> carried in MP-BGP ?

Well here is the answer to the question I asked above: this is the way
to 
tell the PE (and similar VRFs on other PEs) to add the RT 2:2 to all
VPNv4 
prefixes learned from CE routers attached to this VRF when sending
MP-BGP 
updates to other PEs.


>
> 2. Or does this export the ENTIRE set of prefixes in the 'HOSTNAME'
vrf 
> with
> the Extended Community attribute of 2:2 ?

Not quite! The entire set of prefixes consists of those learned from CE 
routers (Rt 2:2 is attached by this PE when sending them to other PEs)
and 
those learned through MP-BGP. The latter have already a set of RTs 
attached. They will not be modified nor will they be sent to other PEs
in 
MP-iBGP.

>
> 3. Does this mean that he RD (rd 100:27) on PE2 for vfr 'HOSTNAME' is 
> only
> locally significant to PE2 ?

No. It is globally (i.e. in the whole world of MPLS VPNs) significant. 
There is however no special meaning to a RD. Its only purpose is to make

VPNv4 (f.e. 100:345:10.1.0.0) globally unique.

>
> and then,
> 4. Does the RT 2:2 determine that all the prefixes contained in vrf
> 'HOSTNAME' will be propagated from PE2 into MP-BGP with Extended 
> Community
> attribute 2:2 ?

Not all prefixes. Only those learned from CEs attached to this VRF. The
PE 
is not allowed to treat all IPv4 prefixes like this, as they might be 
coming from VPNv4 routes learned through MP-BGP - in short, this is
normal 
MP-iBGP loop prevention.


>
>
> Many thanks ,
>
> Dana Konkin
>
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-- 
Dr. Martin Heusinger
Consulting Manager Central European Region
CCIE #5980 CCSI 98285

Global Knowledge
Hungener Str. 6
60389 Frankfurt

Tel.: +49 69 90556700
FAX:  +49 69 90556729

mailto:Martin.Heusinger@GlobalKnowledge.de
web:   www.globalknowledge.de

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