From: William Chen (kwchen@netvigator.com)
Date: Sat Feb 07 2004 - 00:25:59 GMT-3
Dear all,
I was very confused by the IRDP preference. Lower preference value is
better or higher preference value is better?
1. RFC 1256 (http://www.faqs.org/rfcs/rfc1256.html) - A Router
Advertisement includes a "preference level" for each
advertised router address. When a host must choose a default router
address (i.e., when, for a particular destination, the host has not
been redirected or configured to use a specific router address), it
is expected to choose from those router addresses that have the
highest preference level.
2. DocCD
(http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fip
ras_r/1rfipadr.htm#1018753) - Preference value. The allowed range is -231 to
231. The default is 0. A higher value increases the preference level of the
router. You can modify a particular router so that it will be the preferred
router to which other routers will home.
3. Microsoft Clients
(http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnw2kmag00
/html/Redundant2.asp) - An IRDP-enabled computer selects as its default
gateway the router that has the lowest preference number (the lower the
preference number, the higher the preference).
4. Cisco IOS Clients (I can't find a document talking about it) - But,
the lower the preference prefer the higher preference, and positive prefer
the negative. I have tested about it.
5. Solaris 9
(http://docs.sun.com/db/doc/816-0211/6m6nc66sq?q=in.rdisc&a=view) - On a
host, in.rdisc listens on the ALL_HOSTS (224.0.0.1) multicast address for
ROUTER_ADVERTISE messages from routers. The received messages are handled by
first ignoring those listed router addresses with which the host does not
share a network. Among the remaining addresses, the ones with the highest
preference are selected as default routers and a default route is entered in
the kernel routing table for each one of them.
Did the vendors implement their client accroding to the RFC said?
Moreover, in the real lab, should I always configure as DocCD saids? Any
guys with pratical experience in IRDP please comment on this.
Best Regards,
William Chen
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