[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Source address selection in IPv6 multihomed multi-addressed sites
> > However, to enable source address filtering to discard packets with
> > source addresses not belonging to an ISP, it is useful to enable a
> > host, not some intelligent intermediate router, select a source
> > address compatible with an outgoing ISP. For that purpose, intra
> > domain routing protocols or something like that should maintain
> > routing table entries with not only preference values of an external
> > routes, but also proper prefixes to be selected for source
> > addresses,
> > if the entries are chosen by a host.
> > It should be noted that it is already doable with the current OSPF
> > spec.
> Hm, how would that work? In BGP you could see the next hop AS number
> and map this to a source address,
And the information is carried by IGP as has been stated in my draft.
> but in OSPF there is no obvious way
> to do this. (Although I'm sure a non-obvious way can be created.)
You should check the format of AS-external-LSAs, of, say, RFC2740,
where there is a place to hold addresses of outgoing routers.
> However, I certainly wouldn't want hosts to interact with OSPF as this
> is a somewhat fragile protocol. In RIP you can simply ignore what hosts
> have to say and in BGP you can filter it, but in OSPF as-is you can
> only hope the host don't send any information that screws up the
> routing table.
The paragraph above contains so much errors to worth commenting.
> And then there is still the problem of how useful this information is.
> Even today with BGP is is fairly common that BGP selects a very bad
You can use whatever EGP you like, though BGP practically is the
> What BGP doesn't know is that the
> interconnect between B and C is 500 km away while the interconnect
> between D and E is on another continent.
Relying on ASPATHLEN does not address the issue.
On the other hand, BGP administrators know that the interconnect
between B and C is 500 km away while the interconnect between D and
E is on another continent.
However, BGP administrators feel difficulty to grasp connections
between neighbor ASes, if there are so many neighbor ASes.
> Obviously this problem is only
> going to get worse as the routing table becomes smaller. That's why I
> think that there will always be upward pressure for the routing table
The smaller routing table allows more policy based control,
not blindly relying on ASPATHLEN.