Date: Sat, 6 Nov 1999 13:51:37 +0200 From: Tim Priebe <tim@iafrica.com.na> To: chad@DCFinc.com, "Chad R. Larson" <chad@DCFinc.com>, stable@FreeBSD.org Subject: Re: VLAN support in -stable? (fwd) Message-ID: <99110614162802.00318@310.priebe.alt.na> References: <199911051658.JAA23468@freeway.dcfinc.com>
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On Fri, 05 Nov 1999, Chad R. Larson wrote: > 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. I thought this was the solution, I added 4 to ETHER_MAX_LEN, rebuilt the kernel, rebooted. The mtu on the physical interfaces was 1504, so I changed it to 1500. I then reurned the mtu on the sun to 1500, and ran a few simple tests, it looked fine. The following morning, I was told things were a mess. A quick look and the system was running at 100% inturupt, 0% idle. I switched the kernel back, and rebooted, droped the mtu on the sun to 1496, and people could talk to the sun properly again. A little side note the system is still at 100% interupt, so that part of the problem had nothing to do with the change. I will try again as soon as I get some new equipment ready. > > 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. I do not have bpf configured and it ocassionally panics now, but with the system sitting at 100% interupt it may have nothing to do with vlans. Tim. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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