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jamal | 28 Aug 2002 04:59
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Re: conflicting MAC addresses


On Tue, 27 Aug 2002, danny mitzel wrote:

>
> --- jamal <hadi <at> cyberus.ca> wrote:
> >> Has anyone thought about the effect of having two
> pairs
> >> of routers VRRPing for different IPs with an end
> result
> >> of the same VMAC address being used by two routers
> on the
> >> same broadcast domain?
>
> the vrrp protocol receive processing (rfc2338 section
> 7.1)
> specifies:

[..]

>
> >> Actually not concerned about VRRP perse; rather say
> VRRP
> >> and HSRP.
>
> vrrp calculates its vmac using a range of mac
> addresses
> assigned from official ietf OUI.  I can't remember the
>
> hsrp algorithm from memory but I can say it doesn't
> use
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danny mitzel | 28 Aug 2002 05:34
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Re: conflicting MAC addresses


--- jamal <hadi <at> cyberus.ca> wrote:

> A CISCO running HSRP on the same network is
> 00-00-5E-00-01-1F;

the original rfc submitted to document hsrp
(rfc2281) states the hsrp mac is from the cisco 
oui (00:00:0c:07:ac:{hsrp group number}).  from
the latest ios 12.2 docs online this still seems
unchanged.  my only guess would be that someone
has used a 'value add' ios feature 
[e.g. standby mac-address <mac-address>] to 
utilize non-standard hsrp group mac address.  
not a very smart idea IMO.

later,danny

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jamal | 28 Aug 2002 14:28
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Re: conflicting MAC addresses


Danny,
I agree with your point view in general;
Apart from the "value-adding" crowd, this could be a result of a
misconfiguration; the problem is clearly avoided when the OUIs are
known to be owned by vendors who take a lot of care ensuring they dont
get rotated in decade time-frames. How do you do the same for a
MAC address which is reusable like the VRRP ones are? The dangers of
conflict are pretty high as we have seen.

cheers,
jamal

On Tue, 27 Aug 2002, danny mitzel wrote:

>
> --- jamal <hadi <at> cyberus.ca> wrote:
>
> > A CISCO running HSRP on the same network is
> > 00-00-5E-00-01-1F;
>
> the original rfc submitted to document hsrp
> (rfc2281) states the hsrp mac is from the cisco
> oui (00:00:0c:07:ac:{hsrp group number}).  from
> the latest ios 12.2 docs online this still seems
> unchanged.  my only guess would be that someone
> has used a 'value add' ios feature
> [e.g. standby mac-address <mac-address>] to
> utilize non-standard hsrp group mac address.
> not a very smart idea IMO.
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