On Tue, 18 Feb 2003, Petri Helenius wrote:

...

Maybe a stupid question... why would you need GRE tunneling while IPsec has a tunnel mode of its own?

Probably because a major router vendor, despite of repeated customer requests, declined to implement routing across such tunnel mode.

So if the router uses tunnel mode (as per the RFC) despite the GRE tunnel the packet has three IP headers... So that's 160 bits ethernet layer 1 + 18 bytes ethernet layer 2 overhead, 24 bytes for the GRE tunnel, 20 bytes for the IPsec tunnel mode IP header, 10 - 12 bytes for the ESP header, 16 bytes for the initialization vector, 20 bytes for the original IP header and finally 20 bytes for the RTP header. With a 40 byte payload that adds up to 188 bytes on the wire of which 78% is overhead...

--- On Crisco, if memory serves, default payload is 160 for G.711, not 40. The sizing goes in multiples of 80s. Thanks, Christian ***** "The information transmitted is intended only for the person or entity to which it is addressed and may contain confidential, proprietary, and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon, this information by persons or entities other than the intended recipient is prohibited. If you received this in error, please contact the sender and delete the material from all computers."