Subject: Re: Hop Limit = 0

From: [email-masked]
Date: Tue, 26 Mar 2002 19:04:15 +0100

Christophe,

Shouldn't launch this question on the ipv6 mailing list (rather than the 
ipng mailing list) since our question is ipv6 specific, non?

Kind regards,

        Francis.

=================

christophe preguica <[email-masked]>
26/03/2002 14:07

        To:     [email-masked]
        cc:     (bcc: Francis ARTS/BE/ALCATEL)
        Subject:        Hop Limit = 0 

What should be the behavior of a router when it receives an IPv6 packet
with Hop Limit = 0 ? Does IPv6 have the same behavior as for IPv4 TTL ?

Following are some extracts of RFCs.

----------------------------------
(Extract from RFC 1812 -- requirements for ipv4 routers)

4.2.2.9 Time to Live: RFC 791 Section 3.2

   Note in particular that a router MUST NOT check the TTL of a packet
   except when forwarding it.

   A router MUST NOT originate or forward a datagram with a Time-to-Live

   (TTL) value of zero.

   A router MUST NOT discard a datagram just because it was received
   with TTL equal to zero or one; if it is to the router and otherwise
   valid, the router MUST attempt to receive it.

--------------------------------------------
(Extract from RFC 2463 -- ICMPv6)

3.3 Time Exceeded Message

If a router receives a packet with a Hop Limit of zero, or a router
  decrements a packet's Hop Limit to zero, it MUST discard the packet
  and send an ICMPv6 Time Exceeded message with Code 0 to the source of

  the packet.  This indicates either a routing loop or too small an
  initial Hop Limit value.
--------------------------

Kind regards,

Christophe.

---

From: "Dave Thaler" <[email-masked]>
Date: Tue, 26 Mar 2002 10:25:42 -0800

christophe preguica wrote:
> with Hop Limit = 0 ? 

If it's destined to the router itself, accept it.
Otherwise, drop it, and send the ICMPv6 error if the packet wasn't
multicast.

> Does IPv6 have the same behavior as for IPv4 TTL ?

Yes it should be the same.

> If a router receives a packet with a Hop Limit of zero, 

I think the above phrase is incorrect, since it contradicts 2460 as
you pointed out.

>                                                         or a router

-Dave
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