Subject: Time Exceeded and unknown extension headers before the ICMP header

From: "Markku Savela" <[email-masked]>
Date: Fri, 13 Oct 2000 11:16:43 +0300

A router is supposed to send Time Exceeded ICMP when hoplimit goes to zero.

However, it should not send this error, if the packet itself is an ICMP
error, right?

Now, in IPv6 I see a potential problem in implementing above. If there are
unknown extension headers in front of the ICMP, as follows:

  IPv6 [ext. hdrs] ICMP6[Time Exceeded] ...

If the router doesn't implement that particular extension header (for
example AH, but also something totally new), how is it supposed to know that
it should not generate a new ICMP Time Exceeded? (extension headers cannot
be skipped without knowing them, as not all extension headers follow the
same structure).

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From: Francis Dupont <[email-masked]>
Date: Mon, 16 Oct 2000 13:46:33 +0200

In your previous mail you wrote:

   

   
=> this was already discussed in this mailing list. The answer is to
send the Time Exceeded if it is too expensive (or impossible with ESP)
to know if the packet is an ICMP and to rely on ICMP rate limit in order
to keep some bandwidth for other traffic.

[email-masked]