Compression with ssh tunneling



Has anyone done compression testing with ssh tunnels ?

I was looking at it the other day and it looked like the compression options have no effect when you try and use them on a tunnel.

Here was the test:

# ssh -L222:localhost:22 root@server

Then with this tunnel in place I used scp to transfer a file

# scp -P222 root@localhost:/tmp/file1 .

Then I repoeated the test with compression on the tunnel...


# ssh -C -L222:localhost:22 root@server

Then with this tunnel in place I used scp to transfer a file

# scp -P222 root@localhost:/tmp/file1 .

And the speeds were about the same.

If I put the compression on the scp command instead of the tunnel there was a major speed increase.

Is this likely to be because the binary network traffic generated by scp is not very compressable or is it that compression on tunnels does not work ??

I also did some tests with using VNC over a tunnel and also found that there was no visible speed increase when compression was used on the tunnel.

I'd be keen to hear from anyone who has done testing on this and reached a conclusion oneway or the other.

Regards
Dave Gempton.
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