From: Brent Foster (jbrentfoster@yahoo.com)
Date: Fri Mar 31 2006 - 16:19:12 GMT-3
Arun,
Would you please expand on "Step 4"? I'm not clear on
that step.
--Brent
--- Arun Kumar Arumuganainar <aarumuga@hotmail.com>
wrote:
---------------------------------
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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