DHCP Circuit ID - vIOS

[ChrisNewnham_]

I am not sure if this is a vIOS_l2 15.2 specific issue, but when using the command ip dhcp relay information option globally, I found it does insert Agent Remote ID (Option 82 sub-option 2) but does not insert the circuit ID.

I believe it is supposed to do both. Can anyone advise or compare with a physical switch? Thanks!

[MHM Cisco World]

It must be
did you check that in wiresharke ?
MHM

[ChrisNewnham_]

Yep - that's where I saw it.

[MHM Cisco World]

Try add it manually via

Ip dhcp snooping inforomation option format-type circuit-id string xxxx

Then check output in wireshark

MHM

[ChrisNewnham_]

Command is not available (format-type), also format doesn't work.

sw101(config)#ip dhcp snooping information option ?
allow-untrusted DHCP Snooping information option allow-untrusted
format Option 82 information format
<cr>

sw101(config)#ip dhcp snooping information option for
sw101(config)#ip dhcp snooping information option format ?
% Unrecognized command

Also nothing available at interface level either. Thanks

[MHM Cisco World]

2.    ip dhcp snooping

3.    ip dhcp snooping vlan vlan-range []

4.    ip dhcp snooping information option

Are all above command accpet by SW?

Try 

.....Format option 82 ? 

What option you get

MHM

[ChrisNewnham_]

Yeah, I had already tried that too. Even though "format" is listed, if you go beyond it, it says unrecognised as I posted above ^^

sw101(config)#ip dhcp snoop
sw101(config)#ip dhcp snoop vlan 101
sw101(config)#ip dhcp snoop inf
sw101(config)#ip dhcp snoop information op
sw101(config)#ip dhcp snoop information option ?
allow-untrusted DHCP Snooping information option allow-untrusted
format Option 82 information format
<cr>

sw101(config)#ip dhcp snoop information option
sw101(config)#ip dh
sw101(config)#ip dhcp sn
sw101(config)#ip dhcp snooping inf
sw101(config)#ip dhcp snooping information op
sw101(config)#ip dhcp snooping information option ?
allow-untrusted DHCP Snooping information option allow-untrusted
format Option 82 information format
<cr>

sw101(config)#ip dhcp snooping information option form
sw101(config)#ip dhcp snooping information option format ?
% Unrecognized command
sw101(config)#ip dhcp snooping information option format
% Incomplete command.

sw101(config)#ip dhcp snooping information option format options 82
^
% Invalid input detected at '^' marker.

sw101(config)#ip dhcp snooping information option format option82
^
% Invalid input detected at '^' marker.

sw101(config)#ip dhcp snooping information option format option 82
^
% Invalid input detected at '^' marker.

sw101(config)#

[MHM Cisco World]

I think this is same when you use command ""ip dhcp snooping information option format"" under interface ?

MHM

[ChrisNewnham_]

There's no option to do that, I did try the subscriber-id but that's option 6, the circuit ID is option 1

sw101(config)#ip dhcp snoop
sw101(config)#ip dhcp snoop vlan 101
sw101(config)#int vlan 101
sw101(config-if)#ip dh
sw101(config-if)#ip dhcp sn
sw101(config-if)#ip dhcp sn?
% Unrecognized command
sw101(config-if)#ip dhcp sn
sw101(config)#int vlan 101
sw101(config-if)#ip dh
sw101(config-if)#ip dhcp rel
sw101(config-if)#ip dhcp relay ?
information DHCP relay information option
source-interface Set source interface for relayed messages

sw101(config-if)#ip dhcp relay in
sw101(config-if)#ip dhcp relay information ?
check-reply Validate relay information in BOOTREPLY
option DHCP relay information option
option-insert Insert relay information in BOOTREQUEST
policy-action Define reforwarding policy
trusted Received DHCP packet may contain relay info option with zero
giaddr

sw101(config-if)#ip dhcp relay information op
sw101(config-if)#ip dhcp relay information option?
option option-insert

sw101(config-if)#ip dhcp relay information option ?
server-id-override Insert server-id-override and link-selection suboptions
subscriber-id Subscriber identifier sub option
vpn-id Insert VPN sub-opt and change the giaddr to the outgoing
interface

sw101(config-if)#ip dhcp relay information option sub
sw101(config-if)#ip dhcp relay information option subscriber-id ?
WORD Subscriber identifier string

sw101(config-if)#ip dhcp relay information option subscriber-id TEST
sw101(config-if)#

[MHM Cisco World]

There are two port 

L2 port (here you cab use ip dhcp snooping)

L3 interface (vlan svi) ( here you can use ip dhcp relay)

In you network there is no relay so no need ip dhcp relay

Add ip dhcp snooping under port connect to host and check option you get.

MHM

[ChrisNewnham_]

There is a relay, I have a helper-address configured under the SVI of vlan 101.

No dice on the host-facing interface either.

sw101(config)#int po11
sw101(config-if)#ip dh
sw101(config-if)#ip dhcp nso
sw101(config-if)#ip dhcp nso?
% Unrecognized command
sw101(config-if)#ip dhcp snoo
sw101(config-if)#ip dhcp snooping ?
information DHCP Snooping information
limit DHCP Snooping limit
trust DHCP Snooping trust config

sw101(config-if)#ip dhcp snooping in
sw101(config-if)#ip dhcp snooping information ?
option DHCP Snooping information option

sw101(config-if)#ip dhcp snooping information op
sw101(config-if)#ip dhcp snooping information option ?
allow-untrusted DHCP Snooping information option allow-untrusted

[MHM Cisco World]

There is relay 

Then in global 

Ip dhcp relay information option format...

Check option you get

I know it confuse but this how SW add option in case SW is without relay and with relay and I hope after this topic you have good information about dhcp snooping.

MHM

[ChrisNewnham_]

Yep, I do thanks. We are literally going around in circles at this point:

sw101(config)#ip dhcp snooping information op
sw101(config)#ip dhcp snooping information option ?
allow-untrusted DHCP Snooping information option allow-untrusted
format Option 82 information format
<cr>

sw101(config)#ip dhcp snooping information option fo
sw101(config)#ip dhcp snooping information option format ?
% Unrecognized command
sw101(config)#ip dhcp snooping information option format

[MHM Cisco World]

When DHCP snooping is enabled, these Cisco IOS DHCP commands are not available on the switch:

–ip dhcp relay information check global configuration command

–ip dhcp relay information policy global configuration command

–ip dhcp relay information trust-all global configuration command

–ip dhcp relay information option global configuration command <<<- this point 

-ip dhcp relay information trusted interface configuration command

to add circuit-id add new SW with snooping ONLY and under l2 port or in global add the ip dhcp info op format 

[ChrisNewnham_]

I have a L2 only switch the host is connected to. This connects to the L3 switch with the SVI and relay.

It's running the same IOS and has no option to add the circuit ID.

sw110(config)#ip dhcp snooping information op
sw110(config)#ip dhcp snooping information option ?
allow-untrusted DHCP Snooping information option allow-untrusted
format Option 82 information format
<cr>

sw110(config)#ip dhcp snooping information option for
sw110(config)#ip dhcp snooping information option format ?
% Unrecognized command
sw110(config)#i