Subject: issue 17: functions of redirect

From: <[email-masked]>
Date: Wed, 10 Dec 2003 15:07:51 +0200

I have reviewed this issue, and read the relevant parts of RFC
2461. This RFC does indeed contain one of Francis' functions i.e.
specification of a link-layer address for an on-link destination which
has not been advertised as an on-link prefix is:

   Redirect messages are sent by routers to redirect a host to a
   better first-hop router ... or to inform hosts that a destination
   is in fact a neighbor (i.e., on-link).

For the other function, the update of a link-layer address by the
node itelf: The RFC prohibits hosts from sending Redirects:

   A host MUST silently discard any received Redirect message that does
   not satisfy all of the following validity checks:
   
      ...

      - The IP source address of the Redirect is the same as the current
        first-hop router for the specified ICMP Destination Address.

      ...

But I think Francis meant that Neighbor Advertisements should be
used for this purpose.

So what text modifications are necessary? Here's my proposal:

Change

   o  The Redirect function is used for automatically redirecting hosts
      to an alternate router.  Redirect is specified in Section 8 of RFC
      2461 [7].  It is similar to the ICMPv4 Redirect function [15].

=>

   o  The Redirect function is used for automatically redirecting a host
      to a better first-hop router, or to inform hosts that a
      destination is in fact a neighbor (i.e., on-link).  Redirect is
      specified in Section 8 of RFC 2461 [7].  It is similar to the
      ICMPv4 Redirect function [15].

This text has already disappeared through other modifications:

   o  Redirect: This message is always sent from the router's link-local
      address to the source address of the packet that triggered the
      Redirect.  Hosts verify that the IP source address of the Redirect
      is the same as the current first-hop router for the specified ICMP
      Destination Address.  Rules in [1] dictate that unspecified,
      anycast, or multicast addresses may not be used as source
      addresses.  Therefore, the destination address will always be a
      unicast address.

This text has already been changed as well:

      The receiver MUST verify that the Redirect message comes from an
      IP address to which the host may have earlier sent the packet that
      the Redirect message now partially returns.  That is, the source
      address of the Redirect message must be the default router or the
      on-link destination host for traffic sent to the destination of
      the returned packet.  If this is not the case, the message MUST be
      silently discarded.

      This step prevents a bogus router from sending a Redirect message
      when the host is not using the bogus router as a default router.

=>

      Note that RFC 2461 rules already prevent a bogus router from
      sending a Redirect message when the host is not using the bogus
      router as a default router.

I think this would cover all that we need to do. Comments?

--Jari

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