Sören Bleikertz
22 Apr 2010

Notes on Amazon EC2's Network

Shortly after publishing my notes on the EC2 architecture, I was looking into the networking setup of EC2 and in particular figuring out their address schemes. Since I am currently no longer interested in such information, I will publish my incomplete notes and the raw data gathered from about 80 instances in this post. My notes are based on information obtained from small instances in the us-east-1d zone.

IP Address Scheme

I assumed the first hop in the traceroute from a VM is the actual dom0 IP address.

Consider the private IP addresses in the form 10.X.Y.Z. I have noticed that Y is partitioned into blocks containing a /24 for dom0 IP addresses, a /24 for VMs, and a /23 for another set of VMs. For example: 10.208.176/24 is the dom0 range; 10.208.177/24 the first VM range; 10.208.178/23 the second VM range.

Based on my data, the dom0 IP addresses always end in .2 or .3, but there seems to be no pattern between a VM’s IP address and the ending of the corresponding dom0.

MAC Address Scheme

I do not have many information on this one. MAC addresses are typically in the form of 12:31:39:X:Y:Z, where X can be derived from the second octet of the private IP address. The following list gives the value of X for the second IP address octet. As an example: IP 10.210.X.Y leads to 12:31:39:09:X':Y', because 09 is listed for octet 210.

00  254
01  255
02  248
03  249
04  240
05  241
06  208
07  209
09  210
0A  211
0B  214
0C  215

Raw Data

The raw data can be found here. It contains network configuration information (ifconfig, traceroute, and routes) of about 80 instances from the us-east-1d zone. Let me know if you make any interesting discoveries based on that data.