Bridging a Cisco Trunk

Danial Thom danial_thom at
Wed Jan 11 10:48:29 PST 2006

--- Peter Wood <peter at> wrote:

> Dave,
>  > 	I have two cisco switches, configured to
> put ports 2-6 on each of
>  > them into vlan 100. Then I have port 1 on
> both set to trunk between 
> the two
>  > switches. If I have a device on port 2 on
> switch1 it can ping a device on
>  > port 2 on switch2.
> I do this quite often, and it works very well
> on 6.0 for me. You haven't 
> mentioned what version your using, but I will
> assume you have if_bridge. 
> If you don't and you're gonna use this machine
> alot for bridging, I'd 
> recommend moving to 6.0.
> So presumably, you have two interfaces, plugged
> into the trunk port on 
> each cisco. For arguements sake, we'll say you
> have an fxp0 and fxp1.
> So first step is you need to make sure these
> two interfaces are "up", 
> very important, if they arn't, then it wont
> work. It's easy to forget if 
> you arn't assigning IP's to them.
> Remove "polling" if you don't have it compiled
> into the kernel, but 
> again if you're gonna be bridging packets alot,
> get it compiled in. It 
> helps.... alot.
> ifconfig_fxp0="up polling"
> ifconfig_fxp1="up polling"

Here we go again with  polling. If it "helps
alot", did you ever think that maybe interrupt
processing on the OS is broken? Because at best
it should make a nominal difference. We've
already established that FreeBSD doesn't properly
account for CPU usage when polling, so what's
"alot" better about it? fxp controllers are hard
coded to interrupt a maximum of 6000 times per
second, which on a modern CPU isn't going to make
a noticable difference. In fact 1000 HZ ticks per
second probably has just as much overhead with
all the other crap it has to do on each tick.

DragonflyBSD doesn't even support polling because
is *should* be a waste of time (do you think that
Matt Dillon is clueless also?). I'm really
baffled by the lack of understanding of this
subject by virtually everyone in FreeBSDland.


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