"jose orlando t. ribeiro" wrote:
>
> Hi Pierre, Bob!
>
> I hope that everithing is ok now :-)
>
> reading a little more about Bob's problem I had some ideas...
>
> well, Bob needs two routes, from different ISP's cause he's running a
> DNS server, which is tne endpoint from both ISP's...
I'm not grokking... DNS servers are only endpoints for name resolution queries
and there is no requirement for more than one except for redundancy.
> Bob is fiddling his routing configurations in case his route trough the
> DSL goes down he can still works trough the ISP coming from the T1.
Actually, he wasn't... yet...
> Bob is a wayout! To discover all the routes from DSL ISP is even easy...
> that ISP probably is running BGP on his routers... they could configure
> it to propagate theirs routes to BOB... Bob only needs a router capable
> of doing BGP (I don't know if a linux router can do this, I think that
> the cheapest model from Cisco that can do this is the 4700, that has
> discontinued... by the way "cheap" in the cisco way... $$$).
An easier/cheaper way would be for the ISPs to send him just a default route in
a RIP packet. BGP is very complex; eBGP/iBGP needs internal routing protocols
to exchange info between non-adjacent BGP nodes... The reason I didn't suggest
one-way RIP is that there is no way to detect upstream failures; and even if the
ISPs listened to RIP packets from Bob's machine, there is no way to tell him
they stopped arriving... Another option might be OSPF; but again one of the
more complex protocols.
Yet another option is to use per packet load balancing; but with dissimilar
speeds, that's problematic... not to mention one link failing would severely
impede traffic flow...
> Now Bob has a new router, doing BGP, he knows ALL routes from the DSL
> ISP... nothing from that ISP goes to the T1... everything is fine...
The T1 is the primary (faster than DSL)... this sounds like trying to avoid
becoming a transit network... is that what you are saying...? If so, I didn't
hear that being an issue... yet... :^)
Besides, without careful configuration, he could end up with 50,000+ routes....
then, if both ISPs have the same upstream provider, both ISPs could feed him the
same routes...
> then in a dark knight the DSL line goes down... what happens??? BOB
> stops responding requests coming from the DSL ISP's networks.. the same
> filtering/anti-spoof problem...
can't quite grok this...
> What I think Bob should do? Register a second DNS, that one with an ip
> address from the T1 ISP... Bob would respond trough two different
> networks...
Again, DNS has nothing to do with routing or route/packet filtering...
> Happy End! :-)
:^)
> orlando
Pierre
PS: I was starting to forget most of my routing expertise.... slowly coming
back... :^)
