Re: [mif] Some thoughts

[Jan Melen <jan.melen at nomadiclab.com>]

Hi William again,

I'm replying to my own mail sorry for that but forgot one thing from  
the previous mail. If we forget about the failure case then I think  
that the scenario you proposed is valid for MIF meaning that what ever  
mechanism we use to select the source address we should also select  
the default router accordingly regardless whether the routers are on  
the same link or different links of the host. That I think was already  
in the scope of MIF problem statement if I understood correctly Marc  
and Margaret yesterday at WG meeting.

Marc or Margaret may correct me if I've misunderstood something.....

   Regards,
      Jan


On Nov 10, 2009, at 7:00 AM, Jan Melen wrote:

> Hi William,
>
> See inline.....
>
> On Nov 10, 2009, at 6:03 AM, William Herrin wrote:
>
> > On Mon, Nov 9, 2009 at 10:11 PM, liu dapeng <maxpassion at gmail.com>  
> > wrote:
> > > > Routers are hosts too and figuring out how to handle packets to
> > > > multiple upstreams in different administrative domains is important
> > > > there as well. Otherwise we limit ourselves to only the simplest  
> > > > case:
> > > > where no component larger than a single host is a member of two
> > > > networks. As often as not, that isn't the case. The entire local  
> > > > LAN
> > > > can be a member of two upstream networks and it'd be nice if entire
> > > > routed subsystems could be members of two networks.
> > >
> > > In my understanding, router normally does not have the multiple
> > > interfaces issue, since router is designed to forward packets across
> > > different interfaces and there is no default route issue in  
> > > router. so
> > > what problems are you thinking that need to be solved?
> >
> > Hi,
> >
> > Starting from a post-multipath TCP world...
> >
> > The situation that jumps to mind is:
> >
> > 3 offices, A B and C.
> >
> > B connects to A with a T1.
> > C connects to A with a T1.
> > B connects to C with a T1. So they're connected in a triangle.
> >
> > A connects to the Internet with a DSL.
> > B also connects to the Internet with a WiMax link.
> >
> > Server located at C called CS. It has an address from the DSL ISP and
> > an address from the WiMax ISP.
> >
> > CS(DSL)->CA router->AC Router->DSL Router->Internet
> > CS(WiMax)->CB router->BC Router->WiMax Router->Internet
> >
> > But if the CA T1 is down then:
> > CS(DSL)->CA router->CB Router->BC Router->BA Router->AB Router->DSL
> > Router->Internet
>
>
> The CA router can't for the packet that has the source address of  
> the DSL ISP to the CB router. The source address filtering in the  
> WiMax ISP would drop the packet. If the CA router would do  
> translation of addresses it would somewhat work but still the end- 
> host mif function would not have any control. If then again the CA  
> router would replace the source address with the address CS(WiMax)  
> the return packet would come back on a socket that is not open.
>
> Or maybe I misunderstood something from this...
>
> > And while CS has two addresses and network blocks, it has only one
> > ethernet interface on which it talks to both the CA and CB routers.
> >
> >
> > Following me? The routers in the picture have two different routing
> > domains depending on the source address.
>
>
> So far....
>
>
> > Add an Internet cable modem to site C and now you have to handle 3
> > routing domains on every router in the system.
> >
> >
> > But if you keep thinking about it, maybe you don't try to introduce
> > routing domains at all. Maybe you introduce source+destation CIDR
> > pairs instead of just destination CIDRs. So, the DSL at A offers
> > 1.2.3.0/24+0.0.0.0/0, the WiMax at B announces 4.5.6.0/24+0.0.0.0/0
> > and the cable modem at C announces 7.8.9.0/24+0.0.0.0/0. On the flip
> > side, the site-C routers announce 0.0.0.0/0+1.2.3.32/28,
> > 0.0.0.0/0+4.5.6.32/28 and 0.0.0.0/0+7.8.9.32/28. Now there's just one
> > routing domain and six routes which work sensibly in a dynamic  
> > routing
> > protocol.
> >
> > And if CS gets hacked and tries to send a packet to 9.9.9.9 from the
> > forged source address 8.8.8.8, the packet dies at the first router
> > because there's no route for 8.8.8.8/32+9.9.9.9/32.
> >
> > Now if you go back and think of host CS the same way as the routers,
> > CS has the following routes:
> > 1.2.3.35/32+1.2.3.32/28->eth0
> > 1.2.3.35/32+0.0.0.0/0->Router CA metric 2
> > 1.2.3.35/32+0.0.0.0/0->Router CB metric 3
> > 4.5.6.35/32+4.5.6.32/28->eth0
> > 4.5.6.35/32+0.0.0.0/0->Router CB metric 2
> > 4.5.6.35/32+0.0.0.0/0->Router CA metric 3
> > 7.8.9.35/32+7.8.9.32/28->eth0
> > 7.8.9.35/32+0.0.0.0/0->Cable Modem metric 1
> > 127.0.0.0/8+127.0.0.0/8->loopback
>
>
> If any of the default routes fail in such configuration it should be  
> the routing protocol that stops advertising default route through  
> that interface at that point in which case it would result that  
> default route through that interface deprecates in few minutes and  
> the traffic will be routed through another router. Existing  
> connections will break if there is no translation in place in the  
> network see the earlier comments about source address filtering.
>
> DHCP has very poor or non-existing mechanisms to inform the clients  
> about changes in the network routing information as the protocol is  
> designed to be pull instead of push where as all routing protocols  
> are much more appropriate for this type of operation.
>
>   Regards,
>     Jan
>
>
>
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