Subject: mboned: AMT SSM addressing

From: Venketesan <[email-masked]>
Date: Thu, 14 Sep 2006 14:50:00 -0700

Hi,
I had a question about the functioning (fault tolerence) of AMT in a 
certain situation in SSM described below. If one of the authors or 
someone could answer it..

Suppose the unicast address of the gateway is a.b.c.d and is anycast 
prefix is x.y/16. thats makes the possible group addresses available 
for SSM to be 232.c.d/24. Now suppose that this gateway for this 
domain fails and we have another gateway avaialble with unicast 
address a.b.c.e. Now since the G in (S, G) is coupled with the unicast 
address of the gateway, what happnes to the existing connections i.e 
(x.y.a.b, 232.c.d/24). How would they be recovered, how would the 
applications in hosts in remote domains be made aware of the changed 
Group address pool i.e. 232.c.e/24.   

Thanks,
Venkat
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From: John Zwiebel <[email-masked]>
Date: Thu, 14 Sep 2006 15:55:25 -0700

> someone could answer it..

Don't source traffic from an AMT gateway?

FWIW: how do you make the receivers aware of any source/group that
is mashed up by going through this process?

The way I read it, the real source has to be a gateway to make this
work.  If your source breaks, your gateway breaks at the same time.

Setting up a router to be an AMT gateway to provide a source
capability for an entire isolated PIM domain brings up a ton of
other problems.  IMHO, if you want to source enough traffic that
you want to have a backup AMT tunnel, you'd be much better off
getting native multicast.  (Which is the point of AMT -- go native)
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user interface: http://darkwing.uoregon.edu/~llynch/mboned.html
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From: "Sachin K" <[email-masked]>
Date: Fri, 15 Sep 2006 10:40:53 -0500

Hi Venkat,

Even if another gateway tries to backup the failed gateway, the relay may
drop the packets from the new gateway, as it has no state information for
this new gateway.

IMO: another tunnel (through a 3-way handshake) has to be established
between the new gateway and the relay. But according to the AMT draft the
3-way handshake is initiated by the receiver and not the source.
Also SSM itself does not have any fault tolerant mechanism for this
scenario. Correct me if I am wrong on this.

Thanks,
Sachin