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New Member

PIX DHCP Gives Out Its Inside IP To LAN Clients

Hi All,

I have a strange one here. One of my location's PIX firewall is setup to be a DHCP server for LAN clients. However, the PIX gives out its inside interface IP address to cleints requesting an IP address. What happens is there are 2 nodes with the same IP. The PIX inside address is the gateway to the internet- causing other clients to think the workstation is a gateway.

The range for the DHCPD is set to 172.x.x.20-100. The inside IP of th PIX is not in that range.

Anyone know why this is happening. I was told this has been going on since the PIX was installed. It hasn't been a problem until lately.

Any advice would br great!

Thanks,

Vince

5 REPLIES
New Member

Re: PIX DHCP Gives Out Its Inside IP To LAN Clients

DHCPD address pools are bound to an interface and will serve only clients directly connected to that interface.

The pool must be in the same subnet as the interface that you are assigning from.

Hope this helps! Please rate if it does.

New Member

Re: PIX DHCP Gives Out Its Inside IP To LAN Clients

I see your point. I didn't explain myself correctly.

All "x" being equal, the IP of the inside interface is 172.16.x.2. The pool is 172.16.x.20 to 172.16.x.100.

The PIX gives out it's own inside interface IP of 172.16.x.2 to a client requesting an IP. 172.16.x.2 is not even in the pool.

See what I mean? That's not normal. It's like a MS DHCP server giving out its own static IP to a workstation. It's a software problem.

All the PIX are using 6.3(4). This is the only one having this issue.

Thanks for your reply.

New Member

Re: PIX DHCP Gives Out Its Inside IP To LAN Clients

ok, lets confirm some things:

The pix is operating as a DHCP server only, not a client or proxy.

all clients are directly connected to the subnet of the inside interface

If all those things are true, I would like to view your config if possible.

New Member

Re: PIX DHCP Gives Out Its Inside IP To LAN Clients

It's configured with PPPoE on the outside to aquire an IP from the ISP.

All clients are connected to the same subnet as the inside IP.

See attchaed.

Thanks.

V.

New Member

Re: PIX DHCP Gives Out Its Inside IP To LAN Clients

ok, after looking at your config, I dont find any configuration problems. I would clear out the DHCP settings on the internal interface and save the config. Reboot. Put the config back in and see what happens. I have checked and cannot find any bugs related to your issue.

I would also make sure that no other DHCP servers are on the inside network that could interfere with this, and also make sure that the IP address obtained from the ISP is not within the range of the DHCP pool for the inside range.

If it still doesnt work, its time for a TAC call.

Hope that gets you help in the right direction.

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