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SubjectRe: Patch for route.c
On Mon, 7 Apr 1997, Stephen R. van den Berg wrote:

> "David S. Miller" <davem@jenolan.rutgers.edu> wrote:
> > Date: Thu, 03 Apr 1997 14:49:04 -0500
> > From: "Larry J. Blunk" <ljb@merit.edu>
>
> > This patch was submitted by Dave Madden addressing a problem
> > with legitimate routes getting rejected.

[SNIPPED]
Just a note. If you do NOT have two or more different network paths into
or out of your machine (like two Ethernet cards, etc), you do NOT want
to run `gated`. For some strange reason, it runs by default on Sun machines.
There is no way that a machine with a single connection to a network can
provide a "route" to something on the same wire. To provide such a
"route" results in a large amount of extra traffic because the packets are
duplicated.

When `gated` runs, it advertises that it can provide a route to everything
that it can see, i.e., the local network and the default route (perhaps
to the internet through a Cisco router, etc.). Other machines running
`gated` will change their routing to send packets to the machine that
magically declares that it has such a route, EVEN THOUGH THESE MACHINES
ALREADY HAVE THE SAME STATIC ROUTE! The result is that packets will
go from machine -> machine -> machine -> then finally to the destination.
The result is LAN congestion as the traffic is duplicated by the number
of machines that handle the same stuff on the same wire.

You should have static routes set up to handle traffic on a single wire
if you have only a single wire!

Since `traceroute` only uses IP addresses, not Ethernet hardware addresses,
everything looks fine with traceroute because the IP addresses don't
change during the duplicate routing. You need to use a Network Analyzer,
or Sun's snoop to see what is happening. You will see the same packets
duplicated with different hardware addresses.

We have 600+ nodes here, many of them are Suns. We were having problems
with massive LAN congestion until we reconfigured all the Suns to NOT
run `gated`. The result was a reduction in traffic to less than 1 percent
(yes, 1/100th) of the original overloaded condition.


Cheers,
Dick Johnson
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Richard B. Johnson
Project Engineer
Analogic Corporation
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