On 05/09/06, Mr. Adam ALLEN adam@dynamicinteraction.co.uk wrote:
OpenVPN supports Path MTU Discovery which *should* find the maximum packet size which can be supported, "--mtu-disc yes" I decided I'd rather set a conservative Maximum Segment Size (-mss-fix 1250) to ensure that TCP running through the tunnel always worked.
Ideally you find the maximum packet size and make sure all packets are <= that value.
The packet header:data ratio is higher with smaller MTU's, but it is true that MTU can effect delivery or non-delivery. Not every place in a network will want to spend time fragmenting packets and may elect to drop a packet bigger than it's locally configured mtu.
Adam
Many thanks for this and all other replies. The problem was indeed down to MTU issues: exactly what the fix was in the end I'm not sure. I'll ask Nick tomorrow when he's not being a vet then let you know.
Thanks, Jenny