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Re: source routing honored by hosts? [really: per-interface forwarding]

To: Pekka Savola <pekkas@xxxxxxxxxx>
Subject: Re: source routing honored by hosts? [really: per-interface forwarding]
From: "David Stevens" <dlstevens@xxxxxxxxxx>
Date: Mon, 10 Sep 2001 14:45:04 -0700
Cc: <usagi-users@xxxxxxxxxxxxxx>, <ak@xxxxxx>, <netdev@xxxxxxxxxxx>, <davem@xxxxxxxxxx>
Importance: Normal
Sender: owner-netdev@xxxxxxxxxxx
> (device-specific forwarding toggle might be a good thing too, but
>separate issue to be discussed):

BTW, I came across this bit from RFC2460:

   Note: it is possible, though unusual, for a device with multiple
   interfaces to be configured to forward non-self-destined packets
   arriving from some set (fewer than all) of its interfaces, and to
   discard non-self-destined packets arriving from its other interfaces.
   Such a device must obey the protocol requirements for routers when
   receiving packets from, and interacting with neighbors over, the
   former (forwarding) interfaces.  It must obey the protocol
   requirements for hosts when receiving packets from, and interacting
   with neighbors over, the latter (non-forwarding) interfaces.

I don't see any place for a global "forwarding" flag in this interpretation,
except as a convenience for turning all interfaces on or off. The code (other
than sysctl) I think ought to use per-interface flags.

Whether a router is eligible to be a defaut router should be determined by
a separate flag, "AdvSendAdvertisements" in RFC2461, if the concern was that
a backwater router would become a default router for some hosts. I haven't
looked at radvd to see if it supports that, but by my reading, having IsRouter
true shouldn't by itself add a router to the default-router list for a host. I
thought that was your concern, Alexy-- did I misunderstand your comments?
     It does say that IsRouter being cleared is reason to remove a router
from the default-router list, but I think they should be added only based
on router advertisements. So, having forwarding enabled alone wouldn't mean
hosts would use the router as a default router.

                                              +-DLS



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