During an off-line discussion, a friend of mine wrote: >>> I have just come across a big problem using vlans on a FreeBSD box. >>> The mtu on the vlan interfaces is only 1496 bytes, the problem is >>> that any packets destined for the Interface larger than this are >>> just thrown away. The solution > > It's true that 802.1Q makes packets be 4 bytes longer. However, I've > not found a NIC that can't handle the larger packet, and hubs sure don't > care. The switches think it's just ducky, usually, since they hope to > implement the VLAN feature themselves. Changing the MTU in BSD is the > wrong approach, though. What they need to do is increase the size of > the ethernet header by 4 bytes (ETHER_MAX_LEN). There needs to be a > mechanism by which this may be done without a kernel rebuild, though. > > The thing that really surprised me was that I can send both "tagged" > packets and normal ethernet packets on the same BSD interface! I don't > know why I was so surprised. I have a 3COM 802.1Q-compliant switch with > one of its 10/100 ports configured as a VLAN trunk (so it expects its > packets to have the 4-byte tags) and another of its ports in a specified > VLAN. I built my BSD kernel with support for 24 vlans, and hacked > ifconfig to let me set the vlan number (no tools in the distribution to > do that). I can talk out the switch's port just fine, and I can also > talk to the switch and other things on the normal BSD interface just as > though the tagged packets weren't there. So, the BSD interface sends > both tagged and untagged packets and things on the LAN see the ones they > are supposed to, without the others appearing to be problems. Cool! > > However, if you have bpf configured in your kernel, it will panic > occasionally when doing TCP over tagged packets. I'm looking for info > on that one. > > -Les > > -- > Les Biffle Community Service... Just Say NO! > (480) 585-4099 [EMAIL PROTECTED] http://www.les.safety.net/ > Network Safety Corp., 5831 E. Dynamite Blvd., Cave Creek, AZ 85331 > -crl -- Chad R. Larson (CRL15) 602-953-1392 Brother, can you paradigm? [EMAIL PROTECTED] [EMAIL PROTECTED] [EMAIL PROTECTED] DCF, Inc. - 14623 North 49th Place, Scottsdale, Arizona 85254-2207 To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-stable" in the body of the message
