CFT: new trunk(4)

Andrew Thompson thompsa at
Thu Apr 12 08:36:15 UTC 2007

On Thu, Apr 12, 2007 at 03:59:53PM +0800, Adrian Chadd wrote:
> On 12/04/07, Ian FREISLICH <ianf at> wrote:
> >This is the configuration I'm going to be testing with our provider
> >this morning because FreeBSD can't do link aggregation on VLAN
> >interfaces.  I'm hoping that not having IP data available to the
> >switch will not prevent it from working in our scenario.
> Some switches (I'm sure the Cisco ones, for example) will happily do
> etherchannel packet distribution based on IP header info even if
> they're just configured to switch and not route.
> All it has to "know" about IP is which offsets in the packet
> correspond to what it should be hashing against. And (cisco) switches
> have been blurring the L2/L3 switch boundary for a while (think IGMP
> snooping for a very early example.)

In fec, lacp and loadbalance modes our trunk(4) also distributes using a
hash function, it hashes the vlan tag (if present), src and dst mac
addresses, and the full ip/ipv6 header (if present). See the
trunk_hashmbuf() function for the implementation.

The only trunk mode that isnt safe for frame ordering is roundrobin, and
just alternates ports as the name suggests. OpenBSD has this as the
default which is quite suprising, I changed our default to failover.


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