Subject: [pim] Small doubt regarding the assert

From: "[email-masked]" <[email-masked]>
Date: Tue, 28 Oct 2003 08:38:43 -0500 (EST)

Hi all,
Why does the draft state that. For the data triggered asserts the source address MAY be set to the actual source of the data packet. Why can't it be said that the Source address in the assert for data packet arriving on the olist of a (*, G) state MUST be INADDR_ANY.
Can I know the reason why it should be that way. Is it required to maintain backward compatability?
Thanks in advance
Rajesh.

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From: Isidor Kouvelas <[email-masked]>
Date: Tue, 28 Oct 2003 11:51:13 -0800

If the data packet that triggered the assert was forwarded on the link
by a router with (S,G) state, then a (*,G) assert with an INADDR_ANY
source address will not resolve the forwarding conflict. The reason is
that when the router with the (S,G) state receives the assert it will
not know that it has to respons with an (S,G) assert. 
The forwarding conflict will have to wait to be resolved when the
router with the (*,G) state forwards a data packet onto the link and
the router with the (S,G) state responds with the assert.
By providing the source address of the data packet in the (*,G) assert
you optimise this behaviour by allowing the router with the (S,G)
state to respond immediately thus eliminating the additional delay.

Isidor

"[email-masked]" writes:
>
>Hi all,
>Why does the draft state that. For the data triggered asserts the source addre
>ss MAY be set to the actual source of the data packet. Why can't it be said th
>at the Source address in the assert for data packet arriving on the olist of a
> (*, G) state MUST be INADDR_ANY.

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From: Isidor Kouvelas <[email-masked]>
Date: Tue, 28 Oct 2003 11:51:13 -0800

Isidor

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From: Dino Farinacci <[email-masked]>
Date: Tue, 28 Oct 2003 12:23:13 -0800

>> state to respond immediately thus eliminating the additional delay.

    And what if the Assert source address is not in the PIM neighbor database
    for the interface? A router shouldn't process Assert messages from just
    anyone?

Dino

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From: Dino Farinacci <[email-masked]>
Date: Tue, 28 Oct 2003 12:23:13 -0800

Dino

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From: Isidor Kouvelas <[email-masked]>
Date: Tue, 28 Oct 2003 13:24:51 -0800

>    for the interface? A router shouldn't process Assert messages from just

The source address refers to the source of the data packet that
triggered the assert and not the address of the router that sent the
assert PIM packet. The source address of the PIM packet MUST always be
set. A (*,G) assert is identified as a wildcard by the presence of a
wc bit in the message and may have a non INADDR_ANY S in the (S,G).

Isidor

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From: Isidor Kouvelas <[email-masked]>
Date: Tue, 28 Oct 2003 13:24:51 -0800

Isidor

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From: Dino Farinacci <[email-masked]>
Date: Tue, 28 Oct 2003 14:06:40 -0800

>> triggered the assert and not the address of the router that sent the

   That wasn't clear.

>> The source address of the PIM packet MUST always be set.

    Of course it must be set, how can it not be. You need to be more specific
    and precise in your description. Like what's the value of the source
    address in the Assert message.
   
>> wc bit in the message and may have a non INADDR_ANY S in the (S,G).

    I think you are confusing matters. The original question was asking 
    about the source address of the Assert. You seemed to answer the question
    in that context. So that is why I'm confused.

>> wc bit in the message and may have a non INADDR_ANY S in the (S,G).

    This is clear as mud.

Dino

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From: Dino Farinacci <[email-masked]>
Date: Tue, 28 Oct 2003 14:06:40 -0800

That wasn't clear.

   

    This is clear as mud.

Dino

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From: Isidor Kouvelas <[email-masked]>
Date: Tue, 28 Oct 2003 14:23:01 -0800

>    in that context. So that is why I'm confused.

OK lets be more specific. The assert packet format in the current spec
is defined in "4.10.6.  Assert Message Format".  One of the fields *in
the pim assert message* is the "Source Address (Encoded-Unicast
format)".

I think the question was asking why this addres may be something other
than INADDR_ANY for (*,G) asserts.

The answer is:
(*,G) asserts are identified by the R bit in the assert message:
  "R RPT-bit is a 1 bit value. The RPT-bit is set to 1 for Assert(*,G)
     messages and 0 for Assert(S,G) messages."

Hence a (*,G) assert MAY have the Source Address field set to the
source address of the data packet that triggered the assert for the
optimisation reason in my first message.

Now if you think the question was about something else then please
explain what this is along with the answer :-)

thanks
Isidor

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From: Isidor Kouvelas <[email-masked]>
Date: Tue, 28 Oct 2003 14:23:01 -0800

The answer is:

thanks
Isidor

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From: Dino Farinacci <[email-masked]>
Date: Tue, 28 Oct 2003 14:34:08 -0800

>> explain what this is along with the answer :-)

    No, everything is clear now. There were a lot of broken references and you
    don't want me to go down that path.

Dino

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From: Dino Farinacci <[email-masked]>
Date: Tue, 28 Oct 2003 14:34:08 -0800

Dino