Re: Using TTL to Locate Hosts

[Pete Herzog <lists () isecom org>]

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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