PIX 501 dhcp client & Charter cable system

Jan 24, 2005 3 Replies

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Marshall Stacks 21 years ago

I recently moved from a Roadrunner cable network (San Diego) to the Charter network in southern Utah. My PIX 501 refuses to get an IP address from the Charter DHCP servers. I also have a Linksys wireless router and a couple of PCs running 2000/XP. Those devices get their IP addresses from Charter via DHCP with no problem.

Debugging on the PIX shows:

DHCP Offer Message Offered Address: 192.168.100.10 DHCP: Lease Seconds: 15 DHCP: Server ID Option: 192.168.100.1 DHCP: offer received from 192.168.100.1 DHCP: offer has below min lease length: 15. punt DHCP: offer not good enough. punt.... DHCP: SDiscover attempt # 2 for entry:

Looks like the PIX isn't accepting an offer below a minimum lease length. Which is curious because I am running 6.3(4) and a minimum lease length bug (CSCdz09957) was supposedly fixed in 6.3.(1). I have tried

6.3(1),(3), and now (4) but I get the same behavior.

FYI, I had called Charter a couple of times and they cleared out their mac address table for my cable modem so I don't believe the problem is really on the Charter side. It just seems that the PIX is being too picky.

Any thoughts on how I might get this to work? I can put the Linksys on the outside and have the PIX behind the Linksys, but it's just bugging me that I can't get it to work with the PIX on the outside.

Thanks

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Warren 21 years ago

The lease isn't being offered by the Charter DHCP servers. It's being offered by the cablemodem. My guess is you've exceeded the maximum number of CPE's that can be behind the modem.

Let me make sure I've got your configuration right. You have a couple of PC's connected to a router, and the router and the PIX are connected to a hub or switch, which is then connected to the cablemodem. In this configuration, the router would get it's IP address from Charter's DHCP servers, and then would serve the PC's internal IP address to the PC's. If the max CPE for the cablemodem is set for 1, the PIX would not be able to get another IP from Charter, and the cablemodem would default to an attempt to serve a short-leased, temporary IP in the 192.168.100.x range.

Or maybe, since you've said the PC's are getting their IP's from Charter, they're not behind the router. What's connected to the router then? What every is behind the router would get an IP address from the router, not Charter.

Whatever the setup is, the most likely reason for the cablemodem to be attempting to serve the address instead of the Charter network would be that you have too many devices already directly connected to the modem.

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Marshall Stacks 21 years ago

I'm saying that connecting any of my devices directly to the cable modem EXCEPT the PIX works. Individually and one at a time. I am troubleshooting step by step- I don't have everything hooked up at once.

Thanks

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Warren 21 years ago

In that case, each time you change what is connected to the modem, make sure you unplug the modem, and let it sit for 30 seconds before plugging it back in. When you plug it back in, allow it to regain sync before connecting any new equipment to it.

The log except you showed indicates that the PIX isn't communicating past the modem, and is refusing the address that the modem, not the network, is trying to assign to it.

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