configure dhcpclient to send predefine MAC address

[kyiu]

I installed SuSe 6.4 to setup a IP masquerading
firewall. My ISP hand out IP based on a predefined
mac address. How can I modify dhcpclient to send out predefined MAC address?

[Aaron_Adams]

Predefined.. as in an address that doesn't belong to your ethernet card? I don't know that dhcpclient would have a feature where you could spoof the arp packet... that's the only way it can be done I believe. Programs like arpspoof, by dugsong, which is included in the dsniff package can do that. I don't see a program like dhcpclient doing it. That isn't much help, and I'm probably wrong, or misunderstanding, but I'd say it can't be done by normal means.

Waiting to be corrected.

[kyiu]

In RedHat, the host PC uses "pump" to get IP address from the server. In the "ifcfg-ethX" script file, I can configure (among various things) the MACADDR to send to the server for an IP address. I thought, if "pump" can do it, why not dhcpclient. Do you mean dhcpclient can't send a dummy MAC address to the server?

Ken

[Aaron_Adams]

I'd guess no, but that's just me.
I'm sure JimH will know

[JimH]

I installed SuSe 6.4 to setup a IP masquerading
firewall. My ISP hand out IP based on a predefined
mac address. How can I modify dhcpclient to send out predefined MAC address?

DHCP requests from clients always include the clients MAC address. Since the client doesn't have an IP address yet the server uses the MAC address it recieves from the client to respond. Example of what a DHCP server sees from a clent requesting an IP address:

Client sends a DHCPDISCOVER request over the network

Server receives the request from a client:
DHCPDISCOVER from 00:14:98:15:f5:22 via eth0

Server reponds with a DHCPOFFER with an IP address to the client:
DHCPOFFER on 192.168.1.10 to 00:14:98:15:f5:22 via eth0

Client reponds using the IP address it received from the server and asks for permission to use the address:
DHCPREQUEST for 192.168.1.10 from00:14:98:15:f5:22 via eth0

Server responds with an DHCPACK to accept the request or DHCPNAK to deny the request:
dhcpd: DHCPACK on 192.168.1.10 to 00:14:98:15:f5:22via eth0

Client uses DHCPINFORM to request other configuration information:
dhcpd: DHCPINFORM from 192.168.1.10

Red Hat 7.2 uses dhcpcd instead of pump now by default. However if you want to use pump you can install the rpm for it from your Red Hat cds.

Jim H

[Aaron_Adams]

Does that actually answer the question over whether you can define the mac address for dhcpclient to send ? If it does, I'm not thinking straight about this entire subject lol.

Good example of what goes on with DHCP Jim

[JimH]

I am not aware of an option to speciify the mac address to send using dhcpcd or pump. If there was such an option it would basically amount to a built-in hacker tool. :-/

Jim H

[Aaron_Adams]

Ah hah, I wasn't wrong then... That's pretty much what I figured as well. Thus the reference to arpspoof in the dsniff package.

[JimH]

Ah hah, I wasn't wrong then... That's pretty much what I figured as well. Thus the reference to arpspoof in the dsniff package.

Yep. you are correct. ;D Or we are both wrong.

Jim H

[kyiu]

I'm confused. Can dhcpclient send bogus mac address to server or not? I know for fact pump can do it. Many of commercial internet routers (ex: LinkSys) has feature to "clone mac address" for that purpose. do they all use pump?

Ken