Subject: RE: AD comments on draft-ietf-ipv6-router-selection-02.txt

From: "Richard Draves" <[email-masked]>
Date: Thu, 1 Aug 2002 10:55:01 -0700

> Ok, that much I sort of guessed, but is there as simple 
> answer to my followup question:
> 
> - if router2 is not reachable, obviously packets matching prefix2/L
>   can be sent to router1. But, is there any advice on algorithm how
>   the system detects if router2 becomes available? Just wait for RA?
>   Probe with some logic?. (There is no RA in IPv4 -- I think this
>   should work for IPv4 too!)
> 
> Ok, so my address matches the route for router2, but this 
> router is currently unreachable (no entry in neighbor cache). Do I 
> 
> a) drop the packet
> 
> b) if there is a reachable router with shorter matching prefix, send
>    there

As kre points out I think the draft answers your questions, but I want
to followup on one point that should probably be clarified in the draft.
When you say "currently unreachable (no entry in neighbor cache)" it
sounds like you might have a misunderstanding. If the host has no
information about the router's reachability then the host should assume
the router is reachable.

Rich

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From: Markku Savela <[email-masked]>
Date: Thu, 1 Aug 2002 21:30:58 +0300

> From: "Richard Draves" <[email-masked]>

> As kre points out I think the draft answers your questions,

Right, I commented without reading the draft properly :-)

> but I want to followup on one point that should probably be
> clarified in the draft.  When you say "currently unreachable (no
> entry in neighbor cache)" it sounds like you might have a
> misunderstanding. If the host has no information about the router's
> reachability then the host should assume the router is reachable.

Hmm.... the IPv6 neighbor discovery says that after probes fail, entry
should be removed, see RFC-2461 7.3.3

   Upon entering the PROBE state, a node sends a unicast Neighbor
   Solicitation message to the neighbor using the cached link-layer
   address.....
   ..... If no response is received after waiting RetransTimer
   milliseconds after sending the MAX_UNICAST_SOLICIT solicitations,
   retransmissions cease and the entry SHOULD be deleted.

As to 3.4 in internet-drafts/draft-ietf-ipv6-router-selection-02.txt,
it talks only about routers X and Y.

Playing nasty, I imagine situation where I have routers X, Y and Z
(with prefix lengths X > Y > Z) and destination matching all of
them. Now, if only Z is currently reachable, I should probably probe
both X and Y using some logic...