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I am having thew following (simplified) setup: I have a private Subnet where my PC is located. The subnet goes over a virtualized server into the internet. The server uses internally two subnets: One is for internal services and one is some sort of DMZ. Between all subnets there sits (virtual) linux machines that route the traffic. For now, no firewalls were implemented except for the outgoing router. So it looks like this (router3 has firewall):

[PC] -- [router1] -- {subnet int} -- [router2] -- {subnet dmz} -- [router3] -- {wan}

I now did some tests with speeds in the network. I did iperf between my PC and the router1. I get

[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 684 MBytes 574 Mbits/sec

The connections is a gigabit ethernet connections. It may be that the cable is not routed perfectly, so I think this might be ok.

Now I tried with a host inside the int subnet:

[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 381 MBytes 320 Mbits/sec

You see that the traffic is maybe half of the upper value. If I redo things with a virtual box from the dmz subnet, the output is

[ 3] 0.0-10.0 sec 254 MBytes 213 Mbits/sec

So, that's even lower. A direct connection from subnet int to dmz resulted in something like

[ 3] 0.0-10.0 sec 1.00 GBytes 860 Mbits/sec

So my questions are:

  • Is this massive reduction of speed normal?
  • Where could I look for problems? (see below)

I thought of several possible problem sources:

  • The routers are a bit short in virtual RAM as I have not too much physical RAM in the whole box. They have about 80MB of RAM allocated. I could give more but I do not know hoch much is enough.
  • The virtualization is based on XEN. I use bridging for the networking. I did not find any statements if bridging is bad on performance.
  • The virtual subnets are realized as bridges with no physical device added. Same as above. Maybe there exists a better way to create a virtual net in a virtual environment.
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