How much overhead does a VPN tunnel chew?

[gnaveen]

We are receiving about 7.5 Mbps throughtput for direct ip traffic. We now need to configure VPN tunnels. How much overhead can a VPN tunnel take? I am assuming that our overall throughput will be reduced, but not sure how much.
Is there a way to figure it out? What paramters should I look for?

-NG

[dbass]

It is generally based on the hardware platform as to what the throughput is.  The stats are all on cisco.com...you should be able to search and find it.  The packet size overhead is something you'll need to think about as well as it's going to lower your MTU by 56 bytes.  If you add GRE it will be another 24 bytes on top of that. It will definitely have an impact on the hardware...especially at 7.5 Mb.

[sean_evershed]

I agree with dbass but the answer is that it depends on how you configure VPN and the type of traffic traversing the link.

See below:

http://www.cisco.com/en/US/tech/tk827/tk369/technologies_white_paper09186a00800d6979.shtml

"The added header(s) varies in length depending on the IPsec configuration mode but they do not exceed ~58 bytes"

If you refer to the link below a VPN IPSec Tunnel Mode with an Encrypted IP GRE Tunnel can incease the size of a G.711 voice packet by as much as 40%.

http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/IPSecQoS.html#wp56068

Please remember to rate all posts that are helpful

- Sean