Adjusting DHCP Lease Time On DSL-300G ADSL Modem
This page provides information for adjusting the DHCP server lease time on
a DLink DSL-300G Generation II ADSL modem.
DLink DSL-300G Generation II ADSL modem
ADSL Failures
I run a Smoothwall
box behind my ADSL modem, with the Smoothwall's red
interface configured for getting a DHCP IP address from the modem's internal DHCP server.
After upgrading from a trusty DSL-300+ modem to
a newer DSL-300G GenII ADSL modem, I found my Smoothwall
would occasionally fail to reconnect after the ADSL connection briefly dropped out.
The ADSL modem would happily reconnect to my ISP, but Smoothwall's red interface
would continue to hold on to the old IP address it had been given by the modem,
and as a result, Smoothwall could not communicate with the modem or the internet.
The only fix was to reboot Smoothwall, or manually restart Smoothwall's red interface
using
/etc/rc.d/rc.netaddress.down; /etc/rc.d/rc.netaddress.up
The Culprit
Some further investigation found that the DSL-300G modem was giving out DHCP IP addresses
to Smoothwall's red interface with a lease time of 30 days.
This is evident from the DHCP client info on Smoothwall
(in /etc/dhcpc/dhcpcd-eth2.info, where eth2
is the red interface):
LEASETIME=2592000
RENEWALTIME=1296000
REBINDTIME=2268000
However, my DSL-300+ modem only used to give out DHCP IP
addresses with a lease time of 60 seconds, thus ensuring Smoothwall (or any other device
connected to the modem's ethernet port) will immediately notice if the modem's DHCP server
sends notification a new IP address.
Apparently the default DHCP lease time on the DSL-300G is actually 60 seconds, but
it appears that deleting and re-creating the DHCP server configuration in the modem
changes the lease time to 30 days.
Changing The DHCP Lease Time
While you can delete and re-create the DHCP server configuration, there is no way to
change the DHCP lease time via the modem's web interface.
To do so, connect to the modem's telnet server:
telnet 10.1.1.1
Login using admin as the username and password.
To change the DHCP server default and maximum lease times, use the following command:
modify dhcp server pool poolid 0 dlease 60
modify dhcp server pool poolid 0 mlease 60
Save your changes to the modem's flash memory, and reboot the modem to make your
changes take effect:
commit
reboot
Force Smoothwall's red interface to request a new DHCP lease from the modem
by running the following from a command prompt on Smoothwall:
/etc/rc.d/rc.netaddress.down; /etc/rc.d/rc.netaddress.up
and verify the new lease duration by checking in /etc/dhcpc/dhcpcd-eth2.info
on Smoothwall, and you should see something like:
LEASETIME=60
RENEWALTIME=30
REBINDTIME=52
Results
Since making this change, I haven't experienced any futher isolations between Smoothwall
and the DSL-300G modem. Smoothwall always recovers after any ADSL outage.
last updated 28 Oct 2004
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