DHCP puzzle (which component is misbehaving?)

Two days ago, my home network became a notwork. No connectivity to the world, but internal connections were OK - the media server and printer were unaffected. Power-cycling the DSL bridge and router (Linksys WRT54G) didn’t help, so I looked at the router’s config page and found it had no IP. Not, not - it was

To make a long story short, I was able to regain service by setting the router for static IP, even though my ISP recommends DHCP as their IPs are “semi-static,” meaning it is billed as dynamic, but they don’t normally change IPs unless you move or change phone numbers. This is in comparison to their static IP service, where you pay $25 a month more for a guaranteed static IP. In other words, leaving the router set for static IP will probably work indefinitely, but there’s no promises.

The puzzle is why I couldn’t get it to work with DHCP. Is this a failure in the router to obtain an IP, or a failure in the DSL bridge to provide an IP?

Did you try connecting a PC directly to your cable connection? Did it get an IP address? It is possible that your cable co had an outage.

If your router normally has a 192.168.x.x address that’s the internal (LAN) address of the gateway, not the external (public WAN) IP that your ISP would assign it (192.168.x.x is one of the blocks that are non-routable).

So if what used to show 192.168.x.x is now showing it sounds like something is munged up with the DHCP server or NAT functions of your router. Since power cycling the router didn’t work I’d check the DHCP and NAT config pages of the router. A reset to factory defaults might also do the trick, just make sure that you first note down all info that will have to be manually re-entered!

If your router is showing on the WAN screen (that is, where it should be displaying the dynamic address it gets from your ISP) then that indicates some kind of problem between the router and your ISP - like Quart said that sounds like their DHCP server went offline.

What type of address did you have to enter manually to get back online? Was it a 192.168.x.x or something else?

One day my router up and started acting similarly squirrely. Some internet research suggested I go into the modem and set it to “bridge mode”. After I did that, all was well. It’s a little disconcerting that it could wake up one day and decide it needed a significant configuration change, but oh well.

Oftentimes with ISPs, the DHCP servers are logically distant from their nodes. For example, doing simple traceroutes show that my DHCP server is 5 network hops away. Based on the round trip times, it seems that my DHCP server is probably in the Chicago area or thereabouts. This sometimes is a problem as the BOOTP protocol through network gear isn’t very resilient thus requiring many DHCP relay agents (think signal repeaters) throughout the network to move the DHCP packets along. Most home-Internet providers have very shoddy DHCP architecture. on your home router is the result of you not getting an IP address from your ISP due to one of the above reasons. A couple times a year I have to deal with the same thing and it usually comes back after a day or two.

Keep in mind that because you statically defined your external IP address on a network that uses the same addressing scheme as dynamic, you’re eventually going to lose connectivity when that address becomes associated with a different MAC address (someone else’s stuff).

This doesn’t answer your question, but I wonder if you knew that you can install much better formware on the WRT54G - specifically dd-wrt. I bought a WRT454G last week and installed dd-wrt on it so I could use it as a client bridge. It’s the bees tits.

Looks like my ISP was just having a bad few days as I tried kicking the router over to DHCP just now, and it picked up the address immediately. Even picked up a second DNS server name.