Subject: Re: Multiple TCP source addresses?

From: Vernon Schryver <[email-masked]>
Date: Mon, 18 Dec 2000 12:01:38 -0700 (MST)

> From: Harald Koch <[email-masked]>

> ...
> If you run a dynamic routing protocol (even RIP will do with the right
> configuration files), then you can set the default route based on which
> gateway is up and/or primary.
>
> If the primary gateway goes down, the default route will switch to the
> other gateway. At that point, *new* connections will get the new source
> IP address.
>
> The details of "appropriate configuration files" are left as an exercise
> to the reader; IIRC, both zebra and gated have a way to prefer one of
> two equal-cost gateways; this would allow you to set the
> primary/secondary gateway separately on each host on your LAN.

The `routed` daemon in several flavors of UNIX including FreeBSD, NetBSD,
and perhaps OpenBSD will do that by default for IPv4 using RIP, RIPv2,
and Router Discovery.

In flavors of UNIX that make it reasonable to tell whether the host's
Ethernet or other interface is alive (e.g. more packets received and sent
than errors), that `routed` pays attention to the state of interfaces.

Vernon Schryver    [email-masked]

---

From: Joe Touch <[email-masked]>
Date: Wed, 20 Dec 2000 09:15:55 -0800

> Vernon Schryver    [email-masked]

That works only if your interface is UP or DOWN. If it's malfunctioning
or there's a break somewhere else in the LAN (e.g., on the next wire in
a switched ethernet), there's no indication.

It's even worse if you can receive but not send. In that case,
you get RIP announcements and set your route accordingly, but
the packets drop on the floor...

(it would be nice if there were a version that at least tests next-hop 
connectivity in the forward case after receiving an announcement - is
there one that does this??)

Joe