Hardware

All hosts were booted with ALTLinux Sisyphus and 2.4.22-std-up-alt15 kernel.

What is configuration I

+---+              +---+              +---+
| A x--------------x B x--------------x C |
+-x-+              +-x-+              +---+
  . e100     8139too . e100        e100
  . eth0     eth1    . eth0        eth0
  .                  .
  ....................
ipsectun0       ipsectun0

A/eth0: 192.168.0.1/30, default via 10.0.0.2
A/ipsectun0: 10.0.0.1 peer 10.0.0.2
B/eth1: 192.168.0.2/30
B/eth0: 192.168.1.2/30
B/ipsectun0: 10.0.0.2 peer 10.0.0.1
C/eth0: 192.168.1.1/30, default via 192.168.1.2
		
IPSec tunnel is set up between A and B, cipher is 3des-cbc with 192 bits key.

What is configuration II

Almost the same, but B now has 2 e100's and C has 8139too:
+---+              +---+              +---+
| A x--------------x B x--------------x C |
+---+              +---+              +---+
    e100        e100   e100     8139too
		
Addressing plan and interface configuration are the same. IPSec tunnel has the same configuration.

What is test 1

At host B: iperf -s -B 10.0.0.2 -w 10M -f m -i 1 -t 3600
At host A: iperf -c 10.0.0.2 -w 10M -f m -i 1 -t 3600

What is test 2

At host A: iperf -s -B 10.0.0.1 -w 10M -f m -i 1 -t 3600
At host C: iperf -c 10.0.0.1 -w 10M -f m -i 1 -t 3600

test results
configuration test iperf average TCP speed, Mbits/s average system load average interrupts per second
A B C A B C
I 1 70 0.99 0.95 - 1700 7500 -
I 2 66 0.89 0.98 0.10 1200 10000 1900
II 1 71 0.98 1.00 - 2000 1400 -
II 2 68 0.85 0.97 0.06 1300 3700 7200

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