DHCP Option 43

[johnlloyd_13]

hi,

i've never used this command in our wireless/WLC deployments

can someone advise if we really need this (or not) on DHCP pool?

ip dhcp pool WIFI

option 43 ip <WLC IP>

what are some scenarios when you use it and when you don't?

advantage vs disadvantage?

[Leo Laohoo · Accepted solution]

I need this all the time, John.  Particularly when provisioning APs.  

The CON to this is the way DHCP Option 43 is "constructed".  It ain't that easy as putting the IP address in the DHCP pool.  Option 43 is expressed in HEX.

[johnlloyd_13]

pre,

will it work if i set option 43 as IP?

why is the setup working even if i don't put option 43 in the DHCP pool?

is it bcoz of the broadcast?

Translating "CISCO-CAPWAP-CONTROLLER"...domain server (255.255.255.255)

[Sandeep Choudhary · Accepted solution]

NO it will not work if you set it as Option 43 IP.

You must set it in HEX...- option 43 hex <>

On the DHCP server, the vendor specific information is mapped to VCI text strings. When the DHCP server sees a recognizable VCI in a DHCP discover from a DHCP client, it returns the mapped vendor specific information in its DHCP offer to the client as DHCP Option 43. On the DHCP server , option 43 is defined in each DHCP pool (Scope) that offers IP address to the LAPs.

Regards

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[johnlloyd_13]

thanks! our DHCP pool is usually on the CPE router.

will keep in mind it should be in HEX, which is a pain (need conversion)!

[johnlloyd_13]

by the way, does anyone know why the option 43 includes the IP?

why does the router IOS code has it? why not limit only to HEX?

Router(dhcp-config)#option 43 ?
  ascii     Data is an NVT ASCII string
  hex       Data is a hexadecimal string
  instance  Specify the option instance
  ip        Data is one or more IP addresses

[Leo Laohoo]

will it work if i set option 43 as IP?

It's got to be in HEX.  That's the rule and that's the standard.