Subject: Re: New draft on embedding the RP address in IPv6 multicast address

From: Brian Haberman <[email-masked]>
Date: Thu, 10 Oct 2002 14:58:10 -0400

Mike,

Mike O'Connor wrote:
> Brian,
> 
> Is there an underlying assumption that a given group has all of it's
> sources in one PIM domain? 

      In a previous append, I pointed out that there is still an
open issue with a sender being outside of the PIM domain that
allocated the address.

> 
> ASM in V4 doesn't restrict the number of RP's per multicast group. How
> does the proposal support an ASM conference where all participants are
> in different AS/PIM domains and each is both sender and receiver with
> it's own RP?  I'm seeing this as supporting SSM but not ASM.

Why would SSM need an RP?  SSM support is a part of RFC 3306, which
this approach is based on.

Brian

---

From: Gert Doering <[email-masked]>
Date: Thu, 10 Oct 2002 21:39:27 +0200

Hi,

> open issue with a sender being outside of the PIM domain that

Just an idea.  What about sending a PIM register from the sender's RP 
to the RP that belongs to the multicast address?  It would need another 
protocol change, of course.

gert
-- 
Total number of prefixes smaller than registry allocations:  47686  (47095)

SpaceNet AG                 Mail: [email-masked]
Joseph-Dollinger-Bogen 14   Tel : +49-89-32356-0
80807 Muenchen              Fax : +49-89-32356-299

---

From: Brian Haberman <[email-masked]>
Date: Thu, 10 Oct 2002 15:49:02 -0400

> protocol change, of course.

It can lead to a DoS attack on the embedded address.  A bad guy could
embed any address in the multicast address that it wants to attack.
So using register messages would require some type of authentication
mechanism.

Brian

---

From: "Mike O'Connor" <[email-masked]>
Date: Thu, 10 Oct 2002 11:45:11 -0700

[ post by non-subscriber.  with the massive amount of spam, it is easy to
  miss and therefore delete mis-posts.  so fix subscription addresses! ]

Brian,

-Mike 

--
Mike O'Connor,                  E-mail: [email-masked]
Network Engineer                Energy Sciences Network (ESnet)
East coast: +1 631 344-7410     West coast: +1 510 486-7421
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)

-----Original Message-----
From: Brian Haberman [mailto:[email-masked]] 
Sent: Thursday, October 10, 2002 1:56 PM
To: Mike O'Connor
Cc: Marshall Eubanks; Pekka Savola; [email-masked];
[email-masked]; [email-masked]
Subject: Re: New draft on embedding the RP address in IPv6 multicast
address

Mike O'Connor wrote:
> Hi Brian,
> 
> I don't understand how the reciever's RP receives the "owning RP" 
> address for a given multicast group. How are the "owning RP" addresses

> distributed between domains without PIM flooding?

The RP address is embedded in the multicast address.  The key is in the
assignment of multicast addresses in a domain and the configuration of
RP addresses.

So, if a domain uses prefix 3ffe:1:2::/48.  It places an RP in the
network and gives it an address of 3ffe:1:2:3::5.  Now, this RP can be
the RP for the multicast address range FF7x:0540:3ffe:1:2:3::/96. The
key is that the IID portion of the RP's address is set to a value that
can be encode in the RPad field of the multicast address.  The mcast
groups are distinguished by the lower 32 bits of the address.

Now, a receiver's RP can examine the multicast address when it is
creating state and reconstruct the owning RP's address by extracting the
network prefix value and appending the RPad field.

Brian

---

From: "Rami Lehtonen" <[email-masked]>
Date: Fri, 11 Oct 2002 09:27:15 +0300

Hi,

I also see another problem in embedding the RP address in IPv6 multicast
address. Now the sources have to know the address of the RP they are going
to use, when selecting the multicast group address. Is there need for RP
address discovery/announcement?

Another problem that was identified already is that we have only one RP per
group. This means that sources from the another domain than the RP can't use
their own domain RP without RP-RP signalling (e.g. RP-RP Register messages).

Also the receiver domain's RP does not join SPT (S, G) but (RP, G) which
might be suboptimal. It could change afterwards to (S, G) when it learns the
source address but this needs additional state creation signalling
throughout the domains in between.

And last point is that if there are no active sources for that group, this
model allows Internet wide multicast state creation (from receiver(s) in
another domain to the multicast group RP in another domain) compared to the
domain wide state creation in IPv4 MSDP model. This is because we don't have
any source active information available.

- Rami Lehtonen

---

From: Brian Haberman <[email-masked]>
Date: Fri, 11 Oct 2002 18:10:51 -0400

Hi Rami,

> address discovery/announcement?

I don't think so.  Generally, I see applications being assigned
addresses
by network administrators.  That allows the admins to setup their group
to RP mappings.

Other opinions?

> their own domain RP without RP-RP signalling (e.g. RP-RP Register messages).

Right.  That is one of the open issues I pointed out.

> throughout the domains in between.

Actually, most PIM routers switch on the first packet anyway.  So this
approach gives you the same level of support as using MSDP.

> any source active information available.

Good point.  That issue needs to be investigated.

Thanks,
Brian