altq on more than one interface?

[Dave]

Hello,
    I've got a mostly working firewall that filters traffic based on 
interface allowing only selected items in or out. I'd like now to add altq 
in to this, but am uncertain as to which interface to set up queueing on, 
the internal which connects to my 100 mbps switch or the external which goes 
to my cable modem or both? If i use both i'm thinking of using cbq and am 
uncertain how to move traffic from the internal interface's queue for ssh to 
the external interface's queue for ssh and so on.
    Any tips?
Thanks.
Dave.