WAN dhcp renewal problem

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mutiny
DD-WRT Novice


Joined: 31 Mar 2011
Posts: 36

PostPosted: Fri Sep 20, 2013 0:52    Post subject: WAN dhcp renewal problem Reply with quote
I have been having a seemingly awkward problem lately, where my WAN connection seems to reset at exactly the same time, and has been occurring for the past 4 days (I just had the internet service installed 2 days before observing this problem).

I am using dd-wrt fractal build 22208 on a linksys e2000 router, with cable connection from time warner through a motorola sb6141 modem.

What I have observed, is that I have a 24 hour dhcp lease from TWC. My WAN connection seems to reset at exactly the time this lease expires, at exactly the same time every day. The Connection Uptime counter in the WAN status page of dd-wrt will reset to 0. I have tried logging a series of pings from within my network to something like google, starting 10min before and going to 10min after this reset time, and the pings do not stop. However other services such as vpn or connection to a game server will stop momentarily (I can immediately reconnect after this occurs).

Although it is not a long period of disconnect... the fact that a disconnect occurs at all is unnacceptable to me. What exactly is going on here and how do I work with this? Thanks!
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SHoTTa35
DD-WRT User


Joined: 09 May 2011
Posts: 243

PostPosted: Fri Sep 20, 2013 1:08    Post subject: Reply with quote
Seems like your DHCP lease is not renewing when it should which should be 12hrs in your case. Your counter on the WAN page should never reach 0 if everything is working all good.

What I would do is reset the modem and router so that it picks up a fresh 24 then keep an eye to see it renews when it's supposed to. If it's still not then i'd reset at say late at night (you can set a CRON job even) so that the disconnect happens at say 3am when you wont notice.

Maybe it's the build as well, my router renews exactly 1/2 way during it's lease like it supposed to using the latest build from BS.
mutiny
DD-WRT Novice


Joined: 31 Mar 2011
Posts: 36

PostPosted: Fri Sep 20, 2013 1:21    Post subject: Reply with quote
I had the same idea, so that I could monitor the disconnect what I was at home instead of having to probe stuff remotely. However, after powering down both the router and cable modem and leaving off for a bit, after rebooting both I noticed the DHCP lease time did not reset, and the dhcp expiration would once again occur at the usual time the following day. I also always have the same IP every day.

I also run some programs and games over night, so a disconnect even at a seemingly convenient time would not be acceptable for me.
barryware
DD-WRT Guru


Joined: 26 Jan 2008
Posts: 12980
Location: Behind The Reset Button

PostPosted: Fri Sep 20, 2013 1:55    Post subject: Reply with quote
dd-wrt's firewall blocks dhcp renewal requests / responses by default..

This is in the iptables wiki. I use it and it solves the problem (thanks Phuz~)

iptables -I INPUT -p udp --dport 68 -j ACCEPT

save the above to your firewall, not startup.

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mutiny
DD-WRT Novice


Joined: 31 Mar 2011
Posts: 36

PostPosted: Fri Sep 20, 2013 2:48    Post subject: Reply with quote
barryware wrote:
dd-wrt's firewall blocks dhcp renewal requests / responses by default..

This is in the iptables wiki. I use it and it solves the problem (thanks Phuz~)

iptables -I INPUT -p udp --dport 68 -j ACCEPT

save the above to your firewall, not startup.

This is standard behavior? Why would this be a default feature? Is this true for all dd-wrt versions?
LOM
DD-WRT Guru


Joined: 28 Dec 2008
Posts: 7608

PostPosted: Fri Sep 20, 2013 3:55    Post subject: Reply with quote
mutiny wrote:
barryware wrote:
dd-wrt's firewall blocks dhcp renewal requests / responses by default..

This is in the iptables wiki. I use it and it solves the problem (thanks Phuz~)

iptables -I INPUT -p udp --dport 68 -j ACCEPT

save the above to your firewall, not startup.

This is standard behavior? Why would this be a default feature? Is this true for all dd-wrt versions?


Because the firewall does by default not allow any incoming traffic unless there has been an outgoing request from the router beforehand (connection initiated by the router pokes a hole in the firewall allowing the response to get in).

The DHCP renewal is in your case not requested by the router, it is something your ISP pushes onto you a short time before the lease is about to expire.

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mutiny
DD-WRT Novice


Joined: 31 Mar 2011
Posts: 36

PostPosted: Fri Sep 20, 2013 5:35    Post subject: Reply with quote
LOM wrote:
mutiny wrote:
barryware wrote:
dd-wrt's firewall blocks dhcp renewal requests / responses by default..

This is in the iptables wiki. I use it and it solves the problem (thanks Phuz~)

iptables -I INPUT -p udp --dport 68 -j ACCEPT

save the above to your firewall, not startup.

This is standard behavior? Why would this be a default feature? Is this true for all dd-wrt versions?


Because the firewall does by default not allow any incoming traffic unless there has been an outgoing request from the router beforehand (connection initiated by the router pokes a hole in the firewall allowing the response to get in).

The DHCP renewal is in your case not requested by the router, it is something your ISP pushes onto you a short time before the lease is about to expire.

Excellently explained, thank you LOM. This also explains why I did not have this problem with my previous DSL connection? (ISP not forcing renewal in same way, requested by dd-wrt instead?) I'll report back tomorrow when dhcp expires
barryware
DD-WRT Guru


Joined: 26 Jan 2008
Posts: 12980
Location: Behind The Reset Button

PostPosted: Fri Sep 20, 2013 15:43    Post subject: Reply with quote
Thanks LOM.. yea, incoming.. not outgoing.

I wuz having problems when I changed my ISP from DSL to cable. I stumbled across the solution in the iptables wiki when I was looking for a solution for a different problem I wuz having.

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mutiny
DD-WRT Novice


Joined: 31 Mar 2011
Posts: 36

PostPosted: Sat Sep 21, 2013 0:05    Post subject: Reply with quote
Just reporting back that this has solved my particular problem! DHCP lease seems to have renewed around the 13 hour mark, and no longer counts down to 0 and resets, and connection did not drop! Thanks guys
benbun
DD-WRT Novice


Joined: 22 Mar 2007
Posts: 12

PostPosted: Mon Jun 27, 2016 12:05    Post subject: Reply with quote
barryware wrote:
dd-wrt's firewall blocks dhcp renewal requests / responses by default..

This is in the iptables wiki. I use it and it solves the problem (thanks Phuz~)

iptables -I INPUT -p udp --dport 68 -j ACCEPT

save the above to your firewall, not startup.



I have the same Problem with a Linksys WRT-1200 with DD-WRT.
How to do, to save the above to Firewall (I'm a router-newbie) ?

* The "iptables ..." doesn't work for me.
Problem solved => back to the roots
I go back to the original Linksys-firmware and the DHCP-renewal works fine.
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