User:Dennisvd@nikhef.nl/testbed

The testbed currently consists of four physical machines: bleek, toom, kudde and span.

name	type	#cores	mem	OS	disk	remarks
bleek	Intel 5150 @ 2.66GHz	4	8GB	CentOS4-64	software raid1 2×500GB disks	High Availability, dual power supply
toom	Intel E5440 @ 2.83GHz	8	16GB	CentOS5-64	Hardware raid1 2×715GB disks
kudde	Intel E5440 @ 2.83GHz	8	16GB	CentOS5-64	Hardware raid1 2×715GB disks
span	Intel E5440 @ 2.83GHz	8	24GB	CentOS5-64	Hardware raid10 on 4×470GB disks (950GB net)	DHCP,DNS,NFS,LDAP

The network between these machines is a bit particular: They all live in the same VLAN (194.171.96.16/28) but they all have an extra alias interface in the 10.198.0.0/16 range. The Xen DomUs on each of the Xen machines that live in that address range are given connectivity to the other DomUs in the same VLAN without using NAT, and connectivity to the outside with SNAT. Here's an example of the iptables on span:

Chain POSTROUTING (policy ACCEPT 58M packets, 3693M bytes)
 pkts bytes target     prot opt in     out     source               destination         
    0     0 ACCEPT     all  --  any    any     10.198.0.0/16        194.171.96.16/28    
  436 63986 ACCEPT     all  --  any    any     10.198.0.0/16        10.198.0.0/16       
    1   190 SNAT       all  --  any    any     10.198.0.0/16        anywhere            to:194.171.96.28

So all traffic from a DomU on span will appear to have come from span to the outside.

Note that DomUs that have interfaces in the public address range do not need SNAT at all, they simply connect to the hosts xen bridge.