Forwarding w/o promisc on 6.4

Jon Otterholm jon.otterholm at
Sun Apr 19 20:52:58 UTC 2009

On 2009-04-19 11.14, "Robert Watson" <rwatson at> wrote:

> On Sun, 19 Apr 2009, Jon Otterholm wrote:
>> I have a router running 6.4R that does not forward packets if I disable
>> PROMISC on the interface. Hardware is a Dell PE with two Intel 82541EI
>> chipsets (if_em). I have a number (~100) of vlan-interfaces on em0.
>> Everything works as aexpected if I turn on PROMISC on em0 but forwarding
>> stops if I disable it, I can still communicate with the router directly on
>> the same logical network (for example pinging interface adress on a vlan_if
>> from a client on that vlan) but all forwarding stops.
> Try disabling hardware VLAN taggging/processing?  I believe you should be able
> to do this with "ifconfig em0 -vlanhwtag" (substituting appropriate interface
> names).  It could be there's a bug in how hardware-optimized tag handling is
> being managed, as when promiscuous mode is used we re-insert vlan headers in
> software for the benefits of BPF.

I tried doing this without any luck. Running GENERIC kernconf.


> Robert N M Watson
> Computer Laboratory
> University of Cambridge
>> Some info:
>> net.inet.ip.forwarding: 1
>> net.inet.ip.fastforwarding: 0 (enableing this does not help)
>> net.inet.tcp.recvspace=1048576
>> net.inet.tcp.sendspace=1048576
>> kern.ipc.maxsockbuf=16777216
>> I use PF for filtering and disableing this does not help either.
>> Anyone with a clue?
>> //JO
>> _______________________________________________
>> freebsd-net at mailing list
>> To unsubscribe, send any mail to "freebsd-net-unsubscribe at"
> _______________________________________________
> freebsd-net at mailing list
> To unsubscribe, send any mail to "freebsd-net-unsubscribe at"

More information about the freebsd-net mailing list