MAC addr takeover

David Lang dlang at
Fri Oct 16 18:26:38 MDT 1998


the problem is not a changing mac address on a switch port, but the mac
address changing from one switch port to another without (in some cases
like a OS crash) a disconnect from the switch. two examples

3com switch 3000 15 min timeout on a mac address, immediate timeout if the
port is disconnected (link lost on that port)

Cisco Catalyst 5000 15 min timeout on a mac address, no reduction if the
port is disconnected.

everything will clear up in a few min (these values are settable, but if
set to low your switch wasts bandwidth and cpu figuring things out
repeatedly) but during this time there is no way to tell the switch that
the mac address is no longer on one port and is instead on the other port.

Daid Lang

On Fri, 16 Oct 1998, Yiming Zhang wrote:

> Date: Fri, 16 Oct 1998 15:44:48 -0700
> From: Yiming Zhang <yzhang at>
> To: linux-ha at
> Subject: Re: MAC addr takeover
> At 06:23 PM 10/16/98 -0400, you wrote:
> >On Fri, 16 Oct 1998, David Lang wrote:
> >> but on the other hand you have to update the MAC tables in your ethernet
> >> switch if you are using one. is this really easier?
> >
> >It's just a single "task", and you just have to concentrate on making it
> >work with that one type of switch.
> >
> >That beats the heck out of having to deal with a plethora of M$-bred myopic,
> >non-compliant, and just plain stupid/broken networked devices.
> >
> >If your switch is broken (wrt physical address mapping), at least you
> >probably have control over it and can replace it with something that works...
> Agree, 
> HA cannot and should not guarantee broken switch also works.
> Let's forget about HA, in a non-HA setting, if a workstation on LAN changed
> a NIC, and reboot (to send gratuitous ARP), the switch should timely
> capture this mapping (instead of until cache timeout). 
> If this basic need cannot met, the switch should be
> replaced even when we have no HA.
> (But we should mention the broke switch issue in installtion manual).
> Zhang

Version: PGP for Personal Privacy 5.0
Charset: noconv


More information about the Linux-HA mailing list