Subject: RE: draft-hinden-ipv6-host-load-sharing-00.txt

From: Bob Hinden <[email-masked]>
Date: Wed, 14 Nov 2001 16:04:46 -0800

Christian,

>Even if we wanted to somehow mandate load sharing, there are generally
>issues with mandating a round robin approach, or in fact any specific
>algorithm. Round robin has two drawbacks: it hypothesizes that all
>routers are equal, which is very often not the case, and it implies some
>explicit ordering of the requests, which can lead to synchronizations.
>The all routers equal hypothesis is fine for dumb hosts, but smart hosts
>can acquire a knowledge that this or that router usually performs
>better, which is enough to justify a "SHOULD" instead of "MUST". The way
>to avoid synchronization is normally randomization, i.e. pick routers in
>a random order rather than doing round robin.

The issue of all routers not being equal is a generic neighbor discovery 
issue.  Currently a host will add to it's default router list any router it 
receives routing advertisements.  Rich Draves "Default Router Preferences 
and More-Specific Routers" draft addresses this issue and allows a ranking 
of the default routers.

I think load sharing has value when there are multiple (equal preference) 
default routers.  It is very common in the IPv4 world for people to set up 
parallel paths with two or more routers.  In this case it is useful for 
hosts to spread their traffic among these routers.

I will revise the draft to change from round-robin to random order to avoid 
synchronization, and also change it from a MUST to a SHOULD to allow for 
hosts with more information.

Also, it may make sense to later combine this with Rich's draft as they are 
both dealing with related default router selection issues.  In this case 
the load sharing would be done when there are multiple default routers with 
equal preference.

Bob

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