I work for a small ISP and recently have been noticing people reporting their internet going down until they reboot their modems. And when the modems are unresponsive they have a red light. Now we have two different vendors of modems with two models each. This red light issue indicated no ip address on the WAN.
That is just to sum up the issue. So I dug into the issue and the DHCP server. After some captures I was able to find that the DHCP request are hitting the server upon request and getting a valid IP on boot. Ok, good so far. The problem now lies with the lease renew. The request is sent to the server and the server processes it and send out the ACK. The problem now is the host is not getting the ACK. So it sends it until it expires and boom, modem is down.
A few notes
- ip helper is configured for private IP on 1 server interface
- no DHCP snooping
- Relay is setup on access platforms
- DHCP server has a private and public interface and gateway is off public interface.
I am stumped why it the initial lease goes through but the renew does not as both are able to route to the DHCP server. My only thoughts are related to the modem's firewall as the renewal is going through the private IP but leave its public. But then again the tcpdumps on the access platforms dont even show the ACK returning. Also go easy on me as I didnt set this up originally and am a CCNA noob.
No comments:
Post a Comment