Hi Ed,
Take a look at this:
http://www.cisco.com/en/US/docs/switches/lan/catalyst3550/software/release/12.1_19_ea1/configuration/guide/swdhcp82.html#wp1069615
That little blurb explains a bit how DHCP Option 82 is used. For more
detail, consult RFC 3046 (a short read).
Doing a "show ip dhcp snooping" on a switch shows the following as part of
the output:
Insertion of option 82 is enabled
circuit-id default format: vlan-mod-port
remote-id: 001e.7a07.c500 (MAC)
So you can see the default values used for each of the sub-option fields.
These would allow a server to make some sort of decision based on the
information provided in those fields, specifically that the relay was the
"remote-id" with that MAC address, and the circuit ID was something like
452-0-24 for port 24 of module 0 in VLAN 452.
What you referenced as one command is actually two:
(config)#ip dhcp snooping info option format remote {hostname|string {blah}}
and
(config-if)#ip dhcp snooping vlan 500 information option format-type
circuit-id string {blah}
Note one is global and one is interface specific. Once you grok the purpose
of the sub-options, that makes perfect sense.
They can be used to override the default formats for those options listed
above. So you could change the remote-id from a MAC to either the switch
hostname or an arbitrary string like "Columbus-Edge-CPE" and you can modify
the circuit-id to be an interface specific string like "CustID_5555555" or
something like that.
Again, it's so the DHCP server can serve the desired addresses based on the
info it can glean from these hints. See the DHCP class function for how it
could be done on IOS.
Why would you use each? Because the lab tells you to. :-)
For the record I had to research that detail... I knew they were related to
Opt 82 but had to dig around a little bit to figure all that out.
HTH,
Bob
On Wed, May 16, 2012 at 2:25 PM, Bodnar, Edward <[email protected]>wrote:
> Can anybody provide some clarity around these commands.
>
> Ip dhcp snooping information option format-type ( circuit-id | remote-id )
>
>
> Need info on what they do and why I would use them.
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_______________________________________________
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www.ipexpert.com
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www.PlatinumPlacement.com
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