GRE overhead

[kencohen]

I need to create a tunnel between two sites. There is currently a 7140 in one location and a 2621 at another (FastE interfaces used at each end). I'd like to put a GRE tunnel in between the two locations.

I only need the encapsulation, I don't require the security of encryption. Would I get somewhere close to the full 100Mb/s through the tunnel? The customer is most concerned with getting 100Mb/s to their side of the VPN.

[k.poplitz]

GRE is 24 bites overhead so it’s not drastic. I would be more concerned about processor and memory on the 2600. I would guess, since you’re not encrypting the traffic, you’ll get great throughput. Anyone out there with a similar setup?

[gmiiller]

Your 2621 will probably struggle at the throughput figures you've indicated. One thing that will impact hard on the 2600 is the MTU/fragmentation issue, so as far as possible, if there are particular hosts at each end that will be heavy users of the GRE tunnel, consider altering MTU accordingly on them to avoid the need for fragmentation at the routers.

[mli]

As the Cisco 2621 has a performance of 25kpps (probably measured with 64byte packets) the maximum throughput would be: 25000x64x8=12800000 bits/second => 12.8MBit/s