DHCP Option 252

[mlitka]

Has anyone been able to successfully setup DHCP option 252 on a router running DHCP? If so can you provide the statments?

Option 252 is for DHCP WPAD (proxy auto discovery).

[ankbhasi]

Hi Friend,

In order to use the option 252 with DHCP on an IOS based cisco router, the option 252 can be configured on the DHCP pool but only as forwarding agent, you still have to have your microsoft server in place to perform this operations.

You have to provide the ip address of the Windows server that will give away that information, like this:

dhcp pool

option 252 ip X.X.X.X

Please try this out, but make sure the Windows machines have to have the configuration to ask for option 252.

I believe this option is for Microsoft Servers only, so there is no direct way to configure this n the Cisco Router

HTH

Ankur

[mlitka]

Ankur -

Thanks for the info. So in this scenario, can I setup all the other options on the router and just point option 252 to a Microsoft box?

[ankbhasi]

Hi Friend,

What all options you will like to configure? If you can update I will try to find if they are supported and how they work.

Regards,

Ankur

[mlitka]

default-gatway

name-server

wins-server

typical stuff. The question is can I setup a standard scope like this:

ip dhcp pool VLAN1

network 192.168.x.x 255.255.255.0

default-router 192.168.x.x

domain-name mydomain.com

dns-server 10..x.x.x

netbios-name-server 10.x.x.x

netbios-node-type h-node

option 252 xxx

lease 5

But just have 252 point to another server like you mentioned earlier.

[ankbhasi]

Hi Friend,

Yes your config will work fine and all standard things will work like a champ.

HTH

Ankur

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[mlitka]

What I am confused about is that the description of ip is that the data is an ip address, it doesn't sound like it will go to that ip to get the option 252 information

router(dhcp-config)#option 252 ?

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

[ankbhasi]

Hi Friend,

Go ahead and type "option 252 ip ?" and you will get an option to type an ip address. I understand that the description is "DATA" but here it means that the number or data which you enter is an ip address.

Give it a try.

HTH

Ankur

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[mlitka]

Right but is it the IP address that the option will set? Or is it going to go to that IP for the option?

[ankbhasi]

Hi Friend,

Router will work as a forwarding agent for option 252 so whatever ip you specify it will reach that ip to get that option work.

I haven't tried this option though so cannot exactly tell you how packet will look like and how will it work. So I will say give it a try and update us back if it worked for you.

Regards,

Ankur

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[bengeldenhuys]

Hi all,

Please find below the configuration on how to configure option 252 on a DHCP scope for a Cisco Switch or Router.

It look quite simple but please focus on the following:

When configuring the path of the wpad file in the option you will need to configure it with the (“) as per this example: option 252 ascii "http://X.X.X.X/wpad.dat "

NOW:

Make sure after the .dat at the end there is a space before configuring the closing (“).

This is a flaw in Cisco. If you don’t include the space it reads the .dat as a .da –(WPAD will not work)

But by including the space it reads the .dat as .dat

Tested and this works!!

Hope this help

[ashokpatel]

is this problem still exist in latest IOS? I tried with space and it is still not working ...I am still trying to check different way to make sure it is not PFR or Proxy file issue.