Any possibility to remove Option28(Broadcast Address) in DHCP?

[wangbc423]

Any possibility to remove Option28(Broadcast Address) in DHCP if I enable dnsmasq for dhcp?

 

[ColinTaylor]

You can make any changes you like by using a custom config file

https://github.com/RMerl/asuswrt-merlin/wiki/Custom-config-files

 

[wangbc423]

You can make any changes you like by using a custom config file

https://github.com/RMerl/asuswrt-merlin/wiki/Custom-config-files

Thanks. But it seems only "replace", "insert", "append", no delete option.

 

[ColinTaylor]

You could replace a string with spaces or make it a comment. i.e.

pc_replace "dhcp-lease-max=253" "# option removed" $CONFIG

 

[john9527]

Thanks. But it seems only "replace", "insert", "append", no delete option.

replace with a leading # to comment it out....

 

[wangbc423]

You could replace a string with spaces or make it a comment. i.e.

pc_replace "dhcp-lease-max=253" "# option removed" $CONFIG

I want to comment it out with below command. But it has no effect.

pc_replace "dhcp-option=28" "#dhcp-option=28" $CONFIG

 

[octopus]

Try this:

pc_replace "dhcp-option=28" "" $CONFIG

 

[wangbc423]

Try this:

Thanks for your reply. Tried and no effect...Still got Option28

 

[octopus]

show your config file.

 

[ColinTaylor]

show your config file.

And your script (/jffs/scripts/dnsmasq.postconf). What are you using to create the script, vi?

You have rebooted the router?

 

[wangbc423]

And your script (/jffs/scripts/dnsmasq.postconf). What are you using to create the script, vi?

You have rebooted the router?

/jffs/scripts/dnsmasq.postconf

#!/bin/sh
#sed -i "s/cache-size=1500/cache-size=15000/" /tmp/etc/dnsmasq.conf

CONFIG=$1
source /usr/sbin/helper.sh

pc_replace "cache-size=1500" "cache-size=9999" $CONFIG

pc_append "dhcp-option-force=125,00:00:00:00:14:02:06:48:47:57:2d:43:54:0a:02:00:00:0b:02:00:55:0d:02:00:2e" $CONFIG
#pc_append "dhcp-option=28,192.168.2.10" $CONFIG
#pc_replace "dhcp-option=28,192.168.2.255" " " $CONFIG
pc_replace "dhcp-option=28" "" $CONFIG

 

[octopus]

Try to modify dnsmasq-postconf with no comment out string. Do you have dhcp-option=28 in your dnsmasq config file ?

#!/bin/sh
CONFIG=$1
source /usr/sbin/helper.sh

pc_append "dhcp-option-force=125,00:00:00:00:14:02:06:48:47:57:2d:43:54:0a:02:00:00:0b:02:00:55:0d:02:00:2e" $CONFIG
pc_replace "cache-size=1500" "cache-size=9999" $CONFIG
pc_replace "dhcp-option=28" "" $CONFIG

 

[wangbc423]

Try to modify dnsmasq-postconf with no comment out string. Do you have dhcp-option=28 in your dnsmasq config file ?

I think there is no option28 in my config file. It's not my custom option. Seems it's dnsmasq default option. When enable dnsmasq, option28 will be added.

 

[ColinTaylor]

I think there is no option28 in my config file. It's not my custom option. Seems it's dnsmasq default option. When enable dnsmasq, option28 will be added.

You can't edit a string that doesn't exist!

What broadcast address are you trying to set? and why?

 

[ColinTaylor]

Seems it's dnsmasq default option. When enable dnsmasq, option28 will be added.

Correct.

http://www.thekelleys.org.uk/dnsmasq/docs/dnsmasq-man.html

By default, dnsmasq sends some standard options to DHCP clients, the netmask and broadcast address are set to the same as the host running dnsmasq

 

[wangbc423]

Correct.

http://www.thekelleys.org.uk/dnsmasq/docs/dnsmasq-man.html

Yes, I also find this. So we can't remove this broadcast address option?

One of my device will use this broadcast address and it will cause device no internet access. I don't know whether it's device fireware bug.
Now I have two solution:
1. Set dhcp-option=28,192.168.2.10. It's workaround solution and device works fine now.
2. Remove dhcp option 28.

 

[ColinTaylor]

So we can't remove this broadcast address option?

No.

One of my device will use this broadcast address and it will cause device no internet access. I don't know whether it's device fireware bug.

It sounds like a bug because dnsmasq is giving out the correct address, unless you have a non-standard network.

 

[ColinTaylor]

So we can't remove this broadcast address option?

Actually, it looks like I was wrong! The dnsmasq CHANGELOG for release 2.6 says this:

Changed the semantics of argument-less dhcp-options for the default-setting ones, ie 1, 3, 6 and 28. Now, doing eg, dhcp-option=3 stops dnsmasq from sending a default router option at all. Thanks to Scott Emmons for pointing out that this is useful.

So it looks like all you need is

dhcp-option=28

 

[wangbc423]

Actually, it looks like I was wrong! The dnsmasq CHANGELOG for release 2.6 says this:
So it looks like all you need is

dhcp-option=28

Thanks ColinTaylor. I will try it when back home.

 

[wangbc423]

Actually, it looks like I was wrong! The dnsmasq CHANGELOG for release 2.6 says this:
So it looks like all you need is

dhcp-option=28

Amesome!!! It works. Thanks a lot.