Re: Using TTL to Locate Hosts

Hi,

It's a pretty open question. Do you want to know if the machine (networking stack in kernel) is up or the service?

TTL is a guide. When you send a packet, you are looking for a response. That response will contain a TTL. However, you don't know many things about that TTL. The most important thing you don't know is if the TTL was created by the stack on the host or somewhere else, most often a device between you and the host. This device can be proxies for certain ports, like cache proxies for HTTP port 80, or a "firewall".

The good thing is that the TTL if through correlation you can identify where the response came from, you have your probable answer of "up".

There are tools, especially in HPING, that will help you do things such as Fire Walking (there is also a firewalking tool) and loose source routing which both work with "hops" and end-effect TTLs in sending to achieve responses. Something as simple as Traceroute and its derivatives (like TCPtraceroute) especially with attempting certain settings (see the OSSTMM 2.11 modules on Logistics and Enumeration) will aide in eliciting responses. Every response counts as it tells you something about the host.

Sincerely,
-pete.

Chris Hammer wrote:
Hello everyone, I had an interesting question posed to me earlier. The
question was "Could you use only the TTL of a packet to locate hosts and
verify they are up?" I know playing around with Tracert this could be
possible, or a crafted packet using HPING. Any other ideas or thoughts?
Thanks!
Chris

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