Changing DHCP server config on AOS 7

This posting is ~4 years years old. You should keep this in mind. IT is a short living business. This information might be outdated.

The embedded DHCP server on AOS 7 and AOS 8 is a less known feature. But it’s pretty handy in some cases, e.g. if you have no servers on premises, or you don’t want that a a non redundant firewall or router acts as DHCP server. Because you can run two or more switches as a virtual chassis, you can easily make the DHCP server role highly available.

Configuring the DHCP server

The configuration is pretty easy.

-> cd /flash/switch
-> cp dhcpd.conf.template dhcpd.conf
-> vi dhcpd.conf

Edit the dhcpd.conf as necessary. Then start the DHCP server.

-> dhcp-server enable
-> dhcp-server restart

The “enable” enables the DHCP server, but it’s not started. “restart” is used to start or restart the DHCP server.

Change the dhcpd.conf

But how do you change the dhcpd.conf? Sure, simply use VI and edit it. Not quite… After starting the DHCP server, the owner of the dhcpd.conf changes from “admin” to “root”. So with your normal “admin” user, you don’t have the permission to write the file.

In order to change the dhcpd.conf, we need an account with more privileges. In this case, the maintenance shell can help.

Maintenance Shell commands should only be used by Alcatel-Lucent Enterprise personnel or under the direction of Alcatel-Lucent Enterprise.
-> su
Entering maintenance shell. Type 'exit' when you are done.
TOR #-> vi /flash/switch/dhcpd.conf

With higher privileges it’s no problem to edit the dhcpd.conf. Make sure to leave the maintenance shell after the change, and don’t forget to restart the DHCP server.

-> dhcp-server restart

I assume that this behaviour is caused by a bug. I don’t know, if AOS 8 shows the same behaviour. I will update this blog post with further information, as soon as I get them.

Patrick Terlisten
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