Subject: Re: Multiple TCP source addresses?

From: Vernon Schryver <[email-masked]>
Date: Wed, 20 Dec 2000 10:57:29 -0700 (MST)

> From: Joe Touch <[email-masked]>

> ...
> > 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.

> 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.

On the contrary, what I wrote is accurate, based not only on my own testing
of my code, but the quieting of some bug reports and other complaints.
Flavors of UNIX that support the 4.4BSD style interface statistics and
that do a reasonable job of noticing errors do talk to my version of
`routed` and cause it to do the obvious right things, which in some cases
includes switching the interface between UP and DOWN.  Of course, it is
not a panacea.

> 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...

Ethernet drivers that notice missing 10BASE-T and 100BASE-T heartbeats or
coax no-carrier errors such as are cause by partially disconnected cables
cause my `routed` to do the right thing.  Of course, while those are the
most common causes of receive-but-not-send, there are other causes.

> (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??)

That would be hard in RIP, RIPv2, or Router Discovery, although you might
glue some periodic thing with ICMP on the outside.

Blackholes have always been hassles, which may be why they're
mentioned so often in RFC's.

Vernon Schryver    [email-masked]

---

From: Joe Touch <[email-masked]>
Date: Wed, 20 Dec 2000 13:49:39 -0800

> of my code, but the quieting of some bug reports and other complaints.

Only if sent-on-the-floor is recorded as an error. There are
cases where it is not. Ethernet isn't one of these, as you note
later in your reply, but there are others (esp. wireless).

Joe