Subject: Re: WG Action - Accept [LL29] Link-local sources should specify TTL=1

From: Bernard Aboba <[email-masked]>
Date: Mon, 14 Apr 2003 18:11:53 -0700 (PDT)

I agree with Joshua on this one. The impetus for raising this issue was
backward compatibility. There are some implementations that send with TTL=255 and
check it; there are some implementations that send with TTL != 255 (128,
specifically) and don't check it. There are *no* implementations that send
with TTL=1 today.

Given this, it's difficult to see how we promote maximum "backward
compatibility" by choosing an option that *noone* implements. This way
most implementations break, not just some.

Of course, this choice is probably equivalent to deleting all mention of
TTL since I doubt that any implementations will change to support TTL=1.
About the only thing that TTL=1 achieves is to limit global multicast
propagation by packets sourced from an IPv4 LL address. This is somewhat
useful, but hardly a major concern (if it were, it could be special
cased).

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From: "Christian Huitema" <[email-masked]>
Date: Wed, 30 Apr 2003 12:06:32 -0700

> The only implementations doing any checking are checking for TTL 255.

... and failing to interoperate with pre-existing implementations that
don't check the TTL to 255.

Let's face it: there will not be a consensus to set the TTL to any
particular value, including 255. 

-- Christian Huitema