From: Arun Kumar Arumuganainar (aarumuga@hotmail.com)
Date: Fri Mar 31 2006 - 15:53:57 GMT-3
Hi all ,
I would think brent has hit the nail on its head . The real solution to
the problem has been hijacked by our discussion over TE and its related
solution . I think we should think out of the boxhere . I would think ,
the introduction of TE in MPLS VPN set up adds up many problems than it
is intended to solve .
First of all TE solution will not be scable . TE has serious limitation
when it comes to inter-as setup. Hence scalability of the solution is big
question mark . On the other hand we do have a simple and elegant
solution . Let me describe this .
Pls. Note : First build a simple VPN ( with out configuring the backup
link ) . Over that setup perform the following step
Step 1 : Create a BGP Peering ( Either iBGP or eBGP ) using physical
interface of the back up link as the peering address .
Discussion on the configuration :- There is no need to configure
addtional loopback even when your setup is a simple single AS setup .
Pls. Note : Loop Back peering is not a requirement of iBGP it is just an
option . It just gives us a more reliability to the BGP peering during
the events of internal topology changes . In our case there is no need to
protect backup peering and hence we need not use any loopback.
step 2 :- Activate vpnv4 address family for this peering on both sides .
step 3 :- Filter out vpnv4 prefixes so that only the routes belongs to
VRF that are eligible for BACKUP link usage gets advertised . This can be
done in the following ways .
Let us say allowed VRF are has got export RT set to say 100:100 100:101
100:1002 then skeleton configuration will look like this .
router bgp 100
no bgp default ipv4 unicast
neighbor 10.10.10.1 remote-as 100
address-family vpnv4
neighbor 10.10.10.1 activate
neighbor 10.10.10.1 route-map rt-based-filter out
route-map rt-based-filter permit 10
match extcomm 10
ip ext-community 10 permit rt 100:100 100:101 100:102
step 4: use an incoming prefix list and set a very low admin wight for
this peering . This in effect will prevent the backup link to be use when
primary is up .
Pls. Note : This design is very elegant in the sense existing MPLS VPN
setup is not touched at all . Only thing you add is bgp peering for vpnv4
address family. It is also scalable and will work just fine even for
inter-as-vpn .
Thanks and Regards
ARun
--------------------------------------------------------------------
From: "Olopade Olorunloba" <lolopade@ipnxnigeria.net>
Reply-To: "Olopade Olorunloba" <lolopade@ipnxnigeria.net>
To: "'Brent Foster'" <jbrentfoster@yahoo.com>, "'Cisco
certification'" <ccielab@groupstudy.com>, <comserv@groupstudy.com>
Subject: RE: OT: how to filter out several VPNs from a MPLS backbone
backup path
Date: Thu, 30 Mar 2006 21:54:14 +0100
I do not think that you can use this feature.
The ip extcommunity-list is helpful in import and export route-map
configuration. It can help to give a tighter control on which routes
are
imported into which VPN or not.
You could also consider applying the filtering on a per-link basis.
However,
iBGP is often established over loopback addresses, and the actual
link over
which the connection is established is determined by the IGP. Also,
you
would need to have two connections active between the routers,
implying that
both routers would need to have 2 loopbacks addresses. This is
necessary,
since on one connection the desired vpn routes will be filtered out,
and on
the other, they will be the only one permitted.
Asides all these, you will still need to ensure via your IGP, that
one
loopback is reachable across a link, the other loopback across the
other
link. This almost reduces the solution to the previous one. This
scheme
sounds more troublesome to me.
One thing to note is that for a BGP learnt route, the actual
forwarding path
depends on the forwarding path for the BGP next-hop according to the
IGP.
Also, MPLS VPN routes are learnt via BGP, hence to modify the
forwarding
path for the VPN, it is the forwarding path of the BGP next-hop in
the IGP
that needs to be modified.
The use of the BGP next-hop command in the Vrf and the TE tunnel
(unless,
you want to configure static routes all the way from the ingress to
the
egress) seems to me a very good solution.
By the way, I have this solution working on my network.
Regards.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
Brent Foster
Sent: 30 March 2006 16:31
To: Cisco certification; comserv@groupstudy.com
Subject: Re: OT: how to filter out several VPNs from a MPLS backbone
backup
path
So, I think I answered my own question here. See this
link...
http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cr/hirp_r
/rte_bgh1.htm#wp1074763
"The ip extcommunity-list command is used to configure
named or numbered extended community lists. Extended
community attributes are used to filter routes for VPN
routing and forwarding instances (VRFs) and
Multiprotocol Label Switching (MPLS) Virtual Private
Networks (VPNs)."
I'll test this, but I believe this may be a better
solution to the problem.
--Brent
--- Brent Foster <jbrentfoster@yahoo.com> wrote:
> I went back and looked at the original problem
> statement on this thread. We want to restrict
> certain
> VPN traffic from the backup link, right? It might
> even be desirable to have the backup link carry this
> VPN traffic if there is a failure on the primary
> links
> right?
>
> Could there be a different approach using BGP
> filtering techniques since VPNs are simply carried
> as
> MP-BGP routes with route-targets carried as extended
> BGP communities? Could we somehow filter on those
> communities and even use advertise-map/non-exist-map
> techniques to allow the backup link to carry these
> VPNs if there is a failure?
>
> Just thinking out of the box for a different
> solution
> to this problem. It is an interesting one!
>
> --Brent
>
> --- Reinhold Fischer <Reinhold.Fischer@gmx.net>
> wrote:
>
> > On Fri, Mar 24, 2006 at 12:50:28PM +0200,
> > sheherezada@gmail.com wrote:
> > > Hi all,
> > >
> > > I have four routers linked in a row, let's say
> > A-B-C-D, and a lower
> > > bandwidth backup link between A and D. I have
> just
> > added MPLS and set
> > > up several VPNs, but I don't want all VPNs to
> > generate traffic on the
> > > backup link when it comes up. Any idea of how to
> > do it?
> > >
> > > Thanks,
> > >
> > > Mihai
> > >
> >
> > Hi Mihai,
> >
> > here is a possible solution. I have put also the
> > CCIE SP list on CC
> > since this is more a topic for there...
> >
> > - create a second loopback interface on the
> > pe-routers.
> >
> > - add your second loopback interface into your igp
> > so it is reachable
> >
> > - filter your LDP so it is not assigning and
> > distributing any labels
> > for this second loopback
> >
> > - change the next-hop ip-address that bgp will
> > advertise for the
> > VPN that you do not want to have on the
> > low-bandwidth backup link
> >
> > Example> Assuming Lo1 is the Loopback where you
> > are not distributing labels
> > for:
> > !
> > ip vrf TWO
> > rd 2:1
> > route-target export 2:1
> > route-target import 2:1
> > bgp next-hop Loopback1
> > !
> >
> > - at this point this VPN will not work anymore,
> > because you have no
> > LSP to the new Loopbacks
> >
> > - enable MPLS Traffic Engineering, use the new
> > loopback ip as router-id
> > for mpls traffic engineering
> >
> > - build mpls-te tunnels between the new loopback
> > addresses. Use an
> > explicit path that excludes the ip addresses of
> > the low-bandwidth
> > backup link.
> >
> > - at this point the VPN will work again. LSPs are
> > provided through
> > MPLS-TE. As soon as the main link between your
> PE
> > routers goes
> > down the MPLS-TE Tunnel will also go down
> because
> > they are not
> > allowed to signal a path through your
> > low-bandwidth link.
> >
> > hope the explanation is not too confusing.
> >
> > regards
> >
> > reinhold
> >
> >
>
_______________________________________________________________________
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> >
> >
>
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>
>
> Brent Foster
> jbrentfoster@yahoo.com
>
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