Hi Havard,
El 12/11/2007, a las 17:27, Havard Eidnes escribió:
AFAIU, you are essentially proposing to perform source address
based routing by the hosts and by the routers in a multiprefix
site, is that correct?
I don't like the term, because I first do a destination lookup and
only look up the source address in certain cases. Kind of like the
previous comment on source routing, which in IEEE 802.5, DSR, and RFC
791 IP means that the source specifies all or part of the routing
path. I think the term mis-states the case.
But yes, in certain cases where there is a multipath route, the point
is that if the datagram is handed to the wrong ISP and the ISP is
doing ingress filtering, the datagram will be dropped, and hence I
suggest that we direct it toward the right ISP.
But still, you appear to propose to fundamentally change the
forwarding process by inserting a relatively complex lookup
operation into per-packet forwarding, and I think such a change
needs quite a bit more in terms of justification.
Instead, my inclination would be to "solve" this problem in a
much simpler manner, simply by declaring it a configuration
error. A site which receives prefixes from more than a single
provider is clearly multihomed, and needs to have its providers
make appropriate exceptions to a strict "I will only accept
packets with source addresses from within the prefix I delegate"
rule. Either that, or the domain in question needs to ensure via
a combination of address selection and routing policy that one
avoids being subjected to (presumably unwanted) RPF failures.
but which type of sites do you think will have such configuration? I
mean, i would expect that very small multihomed sites may end up with
this configuration, e.g. a home network with dsl and CATV access.
So in this case, i am not sure if the trust needed to release the
ingress filters will exist, so i am not sure the isp will agree to
release them
Regards, marcelo
Regards,
- Håvard
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