Re: Anycast RP

Malick,

Here is what I have found in my testing. It is not by any mean all
inclusive, there may be several other scenarios you can dig into with MBGP
in the mix.

The originator-id is used as the RP address in the SA message. By default,
this is the actual RP address configured/learned on the router. When anycast
RP is being used, this means that the receiving MSDP router receives the SA
message with an address belonging to itself as the RP. This will normally
cause the RPF check on that address to fail because it is received on an
interface that is not local (obviously!). But...afaik, Cisco doesn't
perform RPF checking in this manner by default so it does not matter what
your originator-id is. By default, SAs are excepted even when the RP address
is equal to an address on the receiving MSDP peer.

If you want Cisco to RPF check the RP address in the SA message, use this
command:

R4(config)#ip msdp rpf rfc3618

http://cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide/gt_msdp.html

As an example I have R2 and R4 both at 24.24.24.24 as RPs, using Antonio's
mini labs :) I have no originator-id so the RP in the SA message is
24.24.24.24 by default.

Scenario 1: "no ip msdp rpf rfc3618" (default) on R4

R2 sends an SA...R4 accepts it:

01:18:40: MSDP(0): Received 20-byte TCP segment from 2.2.2.2
01:18:40: MSDP(0): Append 20 bytes to 0-byte msg 92 from 2.2.2.2, qs 1
01:18:40: MSDP(0): 2.2.2.2: Received 20-byte msg 92 from peer
01:18:40: MSDP(0): 2.2.2.2: SA TLV, len: 20, ec: 1, RP: 24.24.24.24
01:18:40: MSDP(0): 2.2.2.2: Peer RPF check passed for single peer
01:18:40: MSDP(0): (10.10.10.1/32, 224.1.1.1), accepted

Scenario 2: "ip msdp rpf rfc3618" on R4

R2 sends the same exact SA...R4 denies it:

01:19:45: MSDP(0): Received 120-byte TCP segment from 2.2.2.2
01:19:45: MSDP(0): Append 120 bytes to 0-byte msg 94 from 2.2.2.2, qs 1
01:19:45: MSDP(0): 2.2.2.2: Received 120-byte msg 94 from peer
01:19:45: MSDP(0): 2.2.2.2: SA TLV, len: 120, ec: 1, RP: 24.24.24.24, with
data
01:19:45: MSDP(0): 2.2.2.2: RPF check failed for 24.24.24.24, we are RP

Notice in both cases, the RP was 24.24.24.24 (the Anycast RP) and it one
case it passed and the other it didn't, depending on the ip msdp rfc3618
command. In scenario #2, you would use the originator-id to specify what
goes in the RP field of the SA message so it would pass the RPF check on R4.

I was testing in with 12.4(23) on 3640s so perhaps there could be different
behaviors across IOS version, but hopefully sheds some light on what you are
looking for.

-hth

On Sun, Mar 28, 2010 at 4:54 PM, Muzammil Malick <malickmuz_at_gmail.com>wrote:

> Thanks Narbik, appreciate the offer but I think I have cracked it!
>
> I tried what you recommended Marko but it didnt work :(
> So I went back to the drawing board and labbed it all again and now its
> working :)
> But after reading about the "ip msdp originator-id" command, I have found 2
> references which suggest that the command should not be the Anycast
> Address,
>
>
> http://www.cisco.com/en/US/docs/ios/solutions_docs/ip_multicast/White_papers/anycast.html
>
> http://www.groupstudy.com/archives/ccielab/200710/msg00110.html
>
> Can you confirm?
> <http://www.groupstudy.com/archives/ccielab/200710/msg00110.html>
>
> On 28 March 2010 22:44, Narbik Kocharians <narbikk_at_gmail.com> wrote:
>
> > Malick,
> >
> > Let me know if you like couple labs on MSDP/Anycast, and i will send it
> to
> > you.
> >
> > On Sun, Mar 28, 2010 at 2:24 PM, Marko Milivojevic <markom_at_ipexpert.com
> >wrote:
> >
> >> On Sun, Mar 28, 2010 at 20:58, Muzammil Malick <malickmuz_at_gmail.com>
> >> wrote:
> >> > The looback0 address.
> >>
> >> Originator-ID needs to be set to the interface you are using as
> >> Anycast-RP. Set it to Lo1 and give it another go. If it doesn't
> >> work... it's ASCII art time. We'll need diagram and all the relevant
> >> configs.
> >>
> >> I'd also like to see "show ip route" from the last-hop router and the
> >> client.
> >>
> >> --
> >> Marko Milivojevic - CCIE #18427
> >> Senior Technical Instructor - IPexpert
> >>
> >> YES! We include 400 hours of REAL rack
> >> time with our Blended Learning Solution!
> >>
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> >>
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> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >
> >
> > --
> > Narbik Kocharians
> > CCSI#30832, CCIE# 12410 (R&S, SP, Security)
> > www.MicronicsTraining.com
> > Sr. Technical Instructor
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-- 
Bryan Bartik
CCIE #23707 (R&S, SP), CCNP
Sr. Support Engineer - IPexpert, Inc.
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