Re: Sharing ISPs

"rg" <rg@xxxxxxxxxxxxx> wrote in message
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"Phillip Windell" <philwindell@xxxxxxxxxxx> wrote in message
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"rg" <rg@xxxxxxxxxxxxx> wrote in message
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This seems to work very well since I can use tracert to see which
gateway is being used for any specific destination. All I had to do was
re-run the SBS connection wizard to make ISA accept this scenario
without complaining!

And so you can yank the network cable on the "external" side of the
functioning NAT box and it switches to the other link? Note, I said the
external side,...because you want the NAT box "itself" to still respond
to the SBS. Bet it does work because the from the SBS view of things the
link is still up because the NAT box is still alive and all the
Dead-Gateway detection cares about is the first "hop" as far as I know.

Any existing connections through the disconnected ISP would fail.

Yes, but it would not jump to the other path because the current "gateway"
is not dead (the "break" is *upstream* from it).

I realized immediately upon posting that the SYN flag can't be used to
influence routing without adding complicated connection tracking to the
router - not the job of the router.

Yes, I think you are getting the point I'm trying to make. Although it *is*
the job of a router because Dynamic Routing Protocols that interact between
the routers that cover multiple redundant pathes to the same destination
will take care of this. What this is not the job of is the Windows OS or a
Firewall Product like ISA Server.

Now with that said some of the later hardware firewalls have mechanism to
handle this that didn't used to exist. Perhaps a future version of ISA will
as well,...but for now it does not. Some of the "home user" NAT Boxes have
this ability to but they are not doing it with traditional Dynamic Routing
Protocols,...so they are using some other method.

Dynamic Routing Protocols need all the involved routers to work together
which means all the the redundant paths have to be under the control of the
same provider,...unless by some miracle two different ISP's would cooperate
together to make it happen.

--
Phillip Windell
www.wandtv.com

The views expressed, are my own and not those of my employer, or Microsoft,
or anyone else associated with me, including my cats.
-----------------------------------------------------


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