> >>> I noticed that the 802.1Q ARP frame size generated by the Linux > > driver > >>> (V1.8) is only 64 octets (not 68 octets). > >>> > >>> It seems the minimum frame size for 802.1Q is 68 octets. > >> The 64-octets is an ethernet physical level issue, not a VLAN issue, > > so > >> there is no need to pad the frame to 68 bytes. > >> > > > > So what happens when a switch untags the vlan tag and sends the untagged > > packet out a port? Is it the responsibility of the switch to then pad > > the packet? Or does this just happen automatically anyway? > > It's the switches duty..and most NIC's hardware will do the padding..I > assume switch hardware can easily do the same. When I first was sent a Cisco 2970-24TS switch when it was brand new, I noticed lots of "too small but good" frames and orange blinking of the port's LED when receiving minimum-sized dot1q frames. It turned out that these switches require 68 byte tagged frames minimum. If they receive 64 Byte frames, they still forward it but complain about it. This is unfortunately not fixable in the IOS because the bug is in the burned-in software on the ASICs. There is a patch around for the e1000 that pads the packets to 68 bytes instead of 64. I guess newer ASICs do not have this bug. Just my $0.02 Sascha
