From: Church, Chuck (cchurch@xxxxxxxx)
Date: Mon May 13 2002 - 18:20:16 GMT-3
I guess that's one of those things where the theory doesn't match what
really happens. I should have known though. A month ago, I had a similar
problem with a duplicate MAC address and HSRP. A colleague configured HSRP
between 2 routers using 2 interfaces on each router, and 2 VLANs. But he
didn't put the group numbers in the HSRP config, so the virtual MAC for both
HSRP pairs was the same. Even though they were different VLANs, the
switches reacted strangely, and HSRP was flapping active between the two
routers. So I guess to be safe, always keep your MACs unique, no matter
where they are. Good catch, Christopher!
Chuck Church
Sr. Network Engineer
CCIE #8776, MCNE, MCSE
US Tennis Association
70 W. Red Oak Lane
White Plains, NY 10604
914-696-7199
-----Original Message-----
From: Christopher M. Heffner [mailto:cheffner@certified-labs.net]
Sent: Monday, May 13, 2002 4:51 PM
To: Church, Chuck
Cc: >CCIE_Lab Groupstudy (E-mail)
Subject: RE: How to Configure a Cisco Router Behind a Non-Cisco Cable
Mode m
Chuck,
You would think since the mac addresses are on two different
segments it would not be a problem but it is.
I ran into the same problem last month with the cable modem and Cisco 2651
router. Had to assign the pcs mac address
to the fa0/0 interface that was connected to the cable modem. I thought the
same thing as you did ... same mac adddress
but two different segments.
The problem is in the arp cache though. Same mac address to two
different ip addresses on the same router in the same
arp cache. Nasty things happen then.
Just thought you like to know.
============================================================================
======
Christopher M. Heffner
Strategic Network Solutions, Inc.
Cisco IMCR Course Director
CCIE, CCSI, MCT, MCSE, MCNI, MCNE, CLI, PCLP, FCSE, ASE, CTT, A+
cheffner@certified-labs.net
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Church, Chuck
Sent: Monday, May 13, 2002 2:58 PM
To: 'Jeff Duchin'; 'Ccielab'
Subject: RE: How to Configure a Cisco Router Behind a Non-Cisco Cable
Mode m
Jeff,
Some cable providers require you to register your MAC address with
them. Try changing the MAC address of the Cisco int to match your PC's.
The duplication shouldn't matter, since they're different physical segments.
You're using 'ip address dhcp' on your interface, right?
Chuck Church
Sr. Network Engineer
CCIE #8776, MCNE, MCSE
US Tennis Association
70 W. Red Oak Lane
White Plains, NY 10604
914-696-7199
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Jeff Duchin
Sent: Monday, May 13, 2002 1:56 PM
To: Ccielab
Subject: How to Configure a Cisco Router Behind a Non-Cisco Cable Modem
Anyone experienced with this?
I've tried this with my 2611 sitting behind my 3Com cable modem, but my
router won't get an IP address for the lofe of it.
Thanks,
Jeff
Jeff Duchin
Design Engineer
WAM!NET Atlantic Region
13600 EDS Drive, 5N-A47
Herndon, VA 20171
Office: (703) 736-4083
Mobile: (301) 305-0122
Fax: (703) 904-4012
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