[c-nsp] DHCP Option 82 Oddities

[Jason Travis]

I had seem that document.
I was hoping someone would have a fix to this "feature" ;)



On Thu, Feb 14, 2008 at 4:09 AM, <sthaug at nethelp.no> wrote:

> > We just turned on DHCP Option 82 on our Cisco switches and we are seeing
> > some oddities in the logs.
> > The switch seems to relay the incorrect port number to the logs.
> > For instance, if a device is connected to 1/0/4, the logs will show
> 1/0/6.
> > The difference of 2 is consistent until we get to higher port numbers,
> > around port 24.  At that point the difference increases to 4.  So if a
> > device is connected to 1/0/40, the log says it's connected to 1/0/44.
> >
> > Has anyone else encountered this error? Is there anything that has to be
> > configured on the switch to fix this?
> > It seems to be an error in the way the switch relays the information.
>
> This is documented (well, at least part of it), and therefore it's a
> feature not a bug :-)
>
> See for instance
>
>
> http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_guide_chapter09186a00808e0574.html#wp1069615
>
> "In the port field of the circuit-ID suboption, the port numbers start
> at 3. For example, on a switch with 24 10/100 ports and small
> form-factor pluggable (SFP) module slots, port 3 is the Fast Ethernet
> x/0/1 port, port 4 is the Fast Ethernet x/0/2 port, and so forth,
> where x is the stack member number. Port 27 is the SFP module slot
> x/0/1, and so forth."
>
> Steinar Haug, Nethelp consulting, sthaug at nethelp.no
>