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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
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.
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.
From: firstname.lastname@example.org [mailto:email@example.com] On Behalf Of
Sent: Thursday, August 12, 2004 3:31 PM
Subject: I-D ACTION:draft-ietf-ipv6-router-selection-05.txt
A New Internet-Draft is available from the on-line Internet-Drafts
This draft is a work item of the IP Version 6 Working Group Working Group of
Title : Default Router Preferences and More-Specific
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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