Leo Song wrote:
Hi, there
We met such a problem, while two Cisco 1720 routers and one
3Com router
are interconnected via a share HUB, in a single collision L2 as
well as
L3 domain, the problem is somehow we can't PING the 3Com router
from any
of Cisco 1720 routers,
Is the 3Com router working correctly in every other way? Maybe the 3Com
software rate-limits ping replies.
but the two Cisco 1720 router can PING
each
other, and we check the ARP table in the two Cisco 1720 routers
and they
does show up the correct APP entry for that 3Com router, and we
have no
access to that 3Com router (so we can't check its ARP table),
the only
thing about the 3Com router is it is correctly configured with
IP
address.
Try an extended ping and make sure that the source address used by the Cisco
router is the one for the shared Ethernet subnet that the 3Com is also on.
Maybe the Cisco router is using a different address that the 3Com doesn't
have a route back to.
Is the Ethernet healthy? Are there lots of errors or other symptoms? Does
show interface ethernet have any other clues? Can you put an anzlyer on the
hub and check for errors as well as check the actual packets?
And after we clear the ARP table in the Cisco 1720 router, then
the PING
to 3Com router is working but, after some time the PING
connectivity
between the Cisco 1720 routers and 3Com router was lost,
That's very strange. But maybe sending the ARP restarts the rate limiting so
it works for a while and then you reach the threshold again.
I
suspect that
is due the ARP problem, (incorrect ARP overwritten, in my
mind).
Why do suspect that? Does it not show the MAC address that you expect for
the 3Com router?
Would
you give me any hits on this problem without access to that 3Com
routers, and solution? I thought to place another Cisco router
to
replace that share HUB would be able to solve this problem and
it'll not
be cost effective. Thanks.
If you replace a hub with a router, you'll have to redo your addressing. A
router connects different L3 networks whereas a hub connects a single
network usually. Well, I guess you could do bridging with the router
instead of routing, and then you wouldn't have to change the addressing, but
that would be an expensive fix.
Priscilla
Best Regards.
Leo
System Engineer.
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