[lug] Linux boxes drop off the net? Router problem?

Gary Frerking (TurboPower) garyf at turbopower.com
Tue Feb 6 12:39:47 MST 2001


>> Ok we're one step closer.  I'm assuming you are using dumb hubs.
(unmanaged) <<

Correct.

>> Some routers/switches use the ARP protocol to keep track of machines
attached to them.  I'm curious if perhaps the linux boxes are not responding
to ARP messages, which is causing them to drop of the network. Switches hubs
ARE intelligent enough to add an entry into their ARP table when they see a
packet coming from a machine attached to them. (This would explain why the
machine shows back up after a ping out from it) <<

I definitely think you're on the right track.

>> You mentioned that you had several security packages installed on all of
the linux machines. Perhaps one of them is filtering ARP messages? <<

Hmmm...

ARP is handled by the kernel, isn't it?

I'm asking to make sure I didn't turn off a daemon or something that handles
it. I have ArpWatch turned off, for example, but I'm pretty sure that's
okay.

Is there some sort of ARP client that I could use from a Linux or Solaris
box to query another and see if/how it responds?

Okay, here's some more [potentially very relevent] info: when I verified
with our SysAdmin that our hubs were unmanaged hubs (and explained why I was
asking) he "happened to mention" that he turned off a bunch of features on
the router some time ago (probably at least a year ago) -- he described the
features to me as "RIP this and ARP that" -- he said he had to turn them off
to resolve some other sort of misrouting issue with our ISP.

Is it possible that he turned off one feature too many, and now the router
*isn't* using ARP to check for connected machines? Windows machines are
obviously noisy enough on the network to keep the router informed of where
they are without ARP. Linux boxes are quiet enough when they're not doing
something that they could be missed, I suppose.

Our SysAdmin is pretty good in many respects, but I think he'd be the first
to say that he falls short of the "guru level" in some areas -- Linux is
definitely one of them, and I don't think he knows everything there is to
know about router configuration either.

-- Gary



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