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Date:      Mon, 30 Jul 2018 00:20:48 -0400
From:      Kurt Lidl <lidl@pix.net>
To:        Maxim Konovalov <maxim.konovalov@gmail.com>, Michael Tuexen <Michael.Tuexen@macmic.franken.de>
Cc:        Randall Stewart <rrs@FreeBSD.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   Re: svn commit: r336465 - in head/sys/netinet: . tcp_stacks
Message-ID:  <91467128-5e84-6518-87ce-5374d410e1af@pix.net>
In-Reply-To: <alpine.BSF.2.20.1807191616560.76318@mp2.macomnet.net>
References:  <201807182249.w6IMns6D076446@repo.freebsd.org> <alpine.BSF.2.20.1807191009050.76318@mp2.macomnet.net> <7FC7DAA2-9B03-4D89-A878-7706EDE4294A@macmic.franken.de> <alpine.BSF.2.20.1807191616560.76318@mp2.macomnet.net>

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On 7/19/18 9:18 AM, Maxim Konovalov wrote:
> On Thu, 19 Jul 2018, 08:09-0400, Michael Tuexen wrote:
> 
>>> On 19. Jul 2018, at 03:12, Maxim Konovalov <maxim.konovalov@gmail.com> wrote:
>>>
>>> Hi Randall,
>>>
>>> On Wed, 18 Jul 2018, 22:49-0000, Randall Stewart wrote:
>>>
>>>> Author: rrs
>>>> Date: Wed Jul 18 22:49:53 2018
>>>> New Revision: 336465
>>>> URL: https://svnweb.freebsd.org/changeset/base/336465
>>>>
>>>> Log:
>>>>   Bump the ICMP echo limits to match the RFC
>>>>
>>> [...]
>>>
>>> Just wonder, are there any practical reasons to do that?
>> In case you send encapsulated packets triggering an ICMP message
>> you actually need more than the 8 bytes which are currently
>> reflected.
> 
> OK, let me rephrase: why do you need more than 8 bytes?  It looks like
> it has been working rather well for 20+ years.

Coming late to the game (I was away for vacation)...

It's handy to have more than 8 bytes of returned payload for ICMP 
packets to allow for more sophisticated network health scanning metrics.

Back when I worked at UUNET, we used the ICMP ECHO REQUEST packets to 
carry accurate timestamps for monitoring dispersion of multicast 
datagrams to select hosts.  I know, ICMP ECHO REQUEST packets have 
required all payload to be returned since at least RFC 1712 - so it's 
not exactly the same as what is being change here...

I imagine that a similar generic treatment of payload data for other 
ICMP type message might be handy too.

-Kurt




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