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RE: I-D ACTION:draft-ietf-ipv6-router-selection-05.txt ---- a question.




In section 3.2 Conceptual Sending Algorithm.
And in the 3.6 Example.

Suggest that a host will send a packet to unreachable router instead of
notifying the upper layer that there is no route to destination. Why is
that?
An alternative would be to send a notification to the application of
Destination Unreachable/ No Route To Destination.

3.2. Conceptual Sending Algorithm for Hosts 

   Type A hosts use the conceptual sending algorithm described in 
   Neighbor Discovery [RFC2461]. 

   When a type B host does next-hop determination and consults its 
   Default Router List, it primarily prefers reachable routers over 
   non-reachable routers and secondarily uses the router preference 
   values.  If the host has no information about the router's 
   reachability then the host assumes the router is reachable. 

   When a type C host does next-hop determination and consults its 
   Routing Table for an off-link destination, it first prefers 
   reachable routers over non-reachable routers, second uses longest-
   matching-prefix, and third uses route preference values.  Again, if 
   the host has no information about the router's reachability then the 
   host assumes the router is reachable. 

   If there are no routes matching the destination (i.e., no default 
   routes and no more-specific routes), then a type C host SHOULD 
   discard the packet and report a Destination Unreachable / No Route 
   To Destination error to the upper layer.

3.6. Example 

   Suppose a type C host has four entries in its Routing Table: 
        ::/0 -> router W with Medium preference 
        2001::/16 -> router X with Medium preference 
        3ffe::/16 -> router Y with High preference  
        3ffe::/16 -> router Z with Low preference 
   and the host is sending to 3ffe::1, an off-link destination. If all 
   routers are reachable, then the host will choose router Y. If router 
   Y is not reachable, then router Z will be chosen and the 
   reachability of router Y will be probed. If routers Y and Z are not 
   reachable, then router W will be chosen and the reachability of 
   routers Y and Z will be probed. If routers W, Y, and Z are all not 
   reachable, then the host should use Y while probing the reachability 
   of W and Z. Router X will never be chosen because its prefix does 
   not match the destination. 


Thanks,
Shuki
-----Original Message-----
From: ipv6-bounces@ietf.org [mailto:ipv6-bounces@ietf.org] On Behalf Of
Internet-Drafts@ietf.org
Sent: Thursday, August 12, 2004 3:31 PM
To: i-d-announce@ietf.org
Cc: ipv6@ietf.org
Subject: I-D ACTION:draft-ietf-ipv6-router-selection-05.txt

A New Internet-Draft is available from the on-line Internet-Drafts
directories.
This draft is a work item of the IP Version 6 Working Group Working Group of
the IETF.

	Title		: Default Router Preferences and More-Specific
Routes
	Author(s)	: R. Draves, D. Thaler
	Filename	: draft-ietf-ipv6-router-selection-05.txt
	Pages		: 13
	Date		: 2004-8-12
	
This document describes an optional extension to Router 
   Advertisement messages for communicating default router preferences 
   and more-specific routes from routers to hosts. This improves the 
   ability of hosts to pick an appropriate router, especially when the 
   host is multi-homed and the routers are on different links. The 
   preference values and specific routes advertised to hosts require 
   administrative configuration; they are not automatically derived 
   from routing tables.

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