Router problem (maybe DHCP related?)

[djh-world]

Hello there.

I've been having problems with my router, basically it doesn't seem to assign DHCP addresses correctly.

Well, at least this is what I think is the problem..

On the network there are 2 computers and one cable modem, one is on Windows XP and then there is this one on Gentoo. The router is downstairs with the modem and on occasion these are turned off at night to conserve power.

Upon switching them back on, and starting up this machine I get a really bizarre IP address from DHCP. Instead of the usual 192.168.1.100, I get something similar to the cable modems IP as if the router was never detected.

This allows me to access the internet, yes, but if the machine downstairs wants to at the same time, it doesn't work because that also cannot see the router properly.

(Also, I cannot access the routers internal settings at this point by going to 192.168.1.1)

But if I shutdown this machine, restart the router and modem then turn on the machine downstairs, Windows finds the router perfectly with no problems and starts the network.

Which brought me to the concern of DHCP being the culprit in this case and I was wondering if anyone had any ideas as to why this is happening.

The router has worked perfectly in the past, this has just been a recent problem of around 2 - 3 weeks.

Thankyou for any help that is received.
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djh-solutions :: freelance web design | solution provider

[NeddySeagoon]

djh-world,

Can you post a sketch of the network topology with the IP addess that get allocated when things are working normally and what you get when you see the problem?
ASCII art is fine.

I also need to know which OS is assoiated with which IP address.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

[djh-world]

Hello there, Thanks for the reply, here is the diagram that you requested.

http://djh-world.com/images/router.png
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djh-solutions :: freelance web design | solution provider

[NeddySeagoon]

djh-world,

I guess that your public IP is assigned by your ISP using DHCP and your router provides Network Address Translation (NAT) from the private 192.168.x.x to your public IP.

It may be a switch on sequence thing. If you switch on the router and modem at the same time, the router will have to wait for its public IP address to be assigned. It may timeout if the modem is not started or your ISP takes a long time to service the DHCP request. In this state it becomes transparent (no NAT) and the Gentoo box picks up the public IP. Thats game over if you are only allowed a single public IP.

Can you make it work by switching on the modem, wait for it to do its startup routine, then switch on the router?
The failure is likely to be intermittent, since it will depend on switch on sequences, your network segment (to your ISP) load, and the load on the ISPs DHCP server.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

[djh-world]

NeddySeagoon

I figured this might of been the problem - the only thing is both router and modem are connected to a multisocket so they both come on at the same time.

The only thing I can think of doing is leaving the power cable out of the router, switch on the modem then the router after that.

Thanks for your help.

(The only bizarre thing is the fact that it has worked perfectly before, but it's only just started now. The only conclusion that I can think of is my ISP is taking longer then usual to retrieve my IP)
_________________
djh-solutions :: freelance web design | solution provider