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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: I-D on operational MTU/fragmentation issues in tunneling
On Mon, Oct 11, 2004 at 11:12:55AM +0300, Pekka Savola wrote: Hi Pekka and others, > Please send comments to me by the end of this week, either on- of > off-list, as you deem appropriate. With the risk of stating the obvious I would say that normally, PMTUD should do the trick. Afterall, there is no real difference between the lower MTU of a tunnel and the lower MTU of any other link. With this in mind, the real problem can be found on networks and hosts that block ICMP-host-unreachables (or simply all ICMP traffic for "security" reasons). Taking this one step further, one might realise that we (as networking community) are looking for a technical solution to compensate for the lack of knowledge of the end-user administrators or webmasters. In my work I have been using tunnels quite a lot, and have delt with a lot if issues regarding PMTUD problems. For end-users behind a tunnel, the best solution is usually to turn PMTUD off completely, such as [[email protected] root]# sysctl -w net.inet.tcp.path_mtu_discovery=0 net.inet.tcp.path_mtu_discovery: 1 -> 0 on a FreeBSD box. I agree that this is far less efficient than it should be, but that's always the flipside of the tunnel-coin. Another option would be to simply strip the DF bit on your tunnel entrance point, but that would be rather undesirable.. -- Sabri Berisha, SAB666-RIPE - I route, therefore you are http://www.cluecentral.net - http://www.virt-ix.net
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