Subject: Join Message

From: "Jyotheeswara Rao Kurma" <[email-masked]>
Date: Mon, 14 May 2001 08:44:57 +0500

Hi All :
  
   I have a small question. Can a Pim router sent a join message, 
saying that I am  interested in joining range of groups. i.e 
group address/prefix length . Some thing similar to what RP can 
advertise . Like I want to be a candidiate RP for the following range 
of groups, which is specified by a group address/prefix length.

I am not sure whether this makes sense or not, because either IGMPv2 , 
v3 won't have any mechanism that lets a host, to say I want listen for 
this group of multicast address in a single join message. 

My question is some thing like this. Join messages will have group 
address, to which they want to join. Can this group address, be a range 
of groups.

Thanks in advance,
Jyotheesh

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Every moment is a golden one for him who has the vision to recognize it 
as such. 
-- Henry Miller

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From: Bill Fenner <[email-masked]>
Date: Sun, 13 May 2001 23:47:43 -0700

The packet format allows for group prefixes, but nobody implements it
so it would be tough to deploy.  One of my todo items for the new spec
is to disallow mask lengths other than those identifying a single group.

  Bill

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From: "Jyotheeswara Rao Kurma" <[email-masked]>
Date: Mon, 14 May 2001 12:00:03 +0500

Hi :

     To realize this I guess, a Pim router has to do some ground work,
i.e it has to see all the group for which it is interested, and then 
decide the prefix lenght etc.. And then send this Join message, instead 
of sending one for each group. 

Thanks Bill,
Jyotheesh

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From: Bill Fenner <[email-masked]>
Date: Mon, 14 May 2001 11:42:51 -0700

The parts that I'm worried about are:

- The router has to determine that the router that it's sending the Join
message to will accept it.  Since not all routers implement lengths other
than 32, there would have to be a new Hello option or something similar
to advertise this capability (and all routers on a LAN would have to
understand it before it was used, so that e.g. prune-override has a
chance to work)

- The ramifications of sending a (*,G-prefix) Join where multiple RP's
handle the groups in the G-Prefix have to be defined.  Does it get
split into multiple messages (good candidate for a DoS attack)?  Does
it get dropped (causing black holes)?

S-Prefix is even worse, since routing table aggregation works against
you.

  Bill