Configuring VLANs - Why is IP address require on NIC connected to Trunk?

Geoff Roberts geoff at
Thu Jun 18 14:01:59 UTC 2009


I am currently using FreeBSD 7.2 - although the configuration below was 
originally configured on FreeBSD 7.0.

I have a working VLAN configuration - two VLANS on one interface.

Let's call the interface ext0 and the VLANS bound to this interface vlan0 and 

The interface ext0 is actually a symbolic name for the real interface (NIC) - 
done using ifconfig_em0_name="ext0" in rc.conf.

I find I have to give the ext0 interface an IP address in order for routing 
and packet filtering to work on the attached VLANs.

a) Is there a way to configure this so that I don't have to give ext0 an IP 

In reality ext0 actually does nothing and has no traffic directed to or from 

I would much rather have ext0 without an IP address, as then I don't have to 
worry about firewall rules etc.

b) If I do have to give the ext0 interface an IP address are there any general 
standards on IP address and mask to specify?

c) Should I also specify firewall rules in pf such as the following or will 
these rules cause other things to break.

block in on ext0 from any to (ext0)
block out on ext0 from (ext0) to any

Kind regards,


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