Subject: RFC 4861: Multicast Router Advertisement

From: "Juan A. Ternero" <[email-masked]>
Date: Thu, 16 Dec 2010 20:34:15 +0100

Dear members:
I have a question about the Router Advertisement sending algorithm of RFC 4861. 
On page 49, it states:

“A router might process Router Solicitations as follows:
- Upon receipt of a Router Solicitation, compute a random delay
within the range 0 through MAX_RA_DELAY_TIME. If the computed
value corresponds to a time later than the time the next multicast
Router Advertisement is scheduled to be sent, ignore the random
delay and send the advertisement at the already-scheduled time.
- If the router sent a multicast Router Advertisement (solicited or
unsolicited) within the last MIN_DELAY_BETWEEN_RAS seconds, ...”

The question is about the second paragraph: “within the last ...”

When does the time start? Does it start from the reception of the Router 
Solicitation or from the computed value in the first paragraph?

-- 
Regards,
Juan A. Ternero

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From: Karl Auer <[email-masked]>
Date: Fri, 17 Dec 2010 09:51:22 +1100

> Solicitation or from the computed value in the first paragraph?

My interpretation is as follows:

The time started when the router *sent* its most recent Router
Advertisement.

As the name suggests, the period is the "minimum delay between router
advertisements". It's designed to rate limit RAs. If the random delay
would result in sending an RA inside that time, ignore the random delay.

Regards, K.

-- 
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Karl Auer ([email-masked])                   +61-2-64957160 (h)
http://www.biplane.com.au/kauer/                   +61-428-957160 (mob)

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From: "Juan A. Ternero" <[email-masked]>
Date: Wed, 29 Dec 2010 19:30:56 +0100

Dear members:
I agree with Karl that one end of the time interval is when the router sent its 
most recent Router Advertisement, and that interval must be less than 
MIN_DELAY_BETWEEN_RAS.

My question was about the other end of the interval.
Is it the computed value in the first paragraph (a random value plus the 
reception of the Router Solicitation), or is it the reception of the Router 
Solicitation?

I think it should be the computed value, but in the text it seems to be the 
reception of the Router Solicitation.

-- 
Regards,
Juan A. Ternero

Karl Auer wrote:
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From: Karl Auer <[email-masked]>
Date: Thu, 30 Dec 2010 10:11:13 +1100

> reception of the Router Solicitation.

So you are asking "when is the *latest* that a router should send an
advertisement after receiving a router solicitation?"

Regards, K.