Otdfbt

You can telnet to an open tcp port on the machine. For instance, if the machine is a web server, and has port 80 open, just:

telnet ip.ad.dre.ss 80

This will work even on encrypted ports (although you won't be able to understand the data)

Some other ports to try are:

• 443 for an https server


• 22 for ssh

(there is a list of ports/services in /etc/services on linux machines)

Run an SNMP agent on the remote machine, and use a manager to read one of the values out of the standard MIB.

If you have not firewalls and routers in the way, i.e., if you're on the same segment as the host you're trying to check - most of the solutions above are a little exhaustive imho.

It doesn't matter what port you connect to, and in fact, if you connect to a port that's unlikely to have a service running, you can get the job done without being detected.

How?

You can use any tool you like, but we can just use telnet...

% telnet <host> 313373
Trying 10.211.55.3...
telnet: connect to address 10.211.55.3: Connection refused
telnet: Unable to connect to remote host
%

This should happen immediately, unless the host is dropping packets. What's actually happening is that the TCP/IP stack on the host is sending you back a TCP segment with the RST bit set - i.e. terminating your SYN packet.

The fact that you received a RST packet means that there is indeed a host up at the other end, and as a bonus - you've done so undetected (The TCP/IP had no upper-layer application to talk to about this connection).

Rather than telnet however, I'd probably use something like scapy, write up something that looks for the RST flag and let's you know.

Just to complete this, if there is no host on the IP that you try - it will hang for a little while, and the timeout - the same thing that would happen if the receiving host had a firewall with a drop filter.

If firewalls are involved, then as others have suggested, make use of tools such as nmap and whatever else.

If you have access to another machine on the same LAN as your target machine, you can use arping.

Arping works by sending ARP packets targeting the machine, this works perfectly because you cannot block arp packets if you want to use the network (well, you can set up static arp tables everywhere :D ) But the downside is you have to be within the same LAN as your arping target.

Are there any services available on the machine? One way to see if a machine is there is to use the telnet client to connect to it, but changing the port you need to hit.

So lets say the machine is running MS SQL which runs on port 1433 by default. You use the following command

telnet machine-name-address 1433

If Telnet connects the the machine is up and running, Doesn't mean it's running properly, but listening to that port nonetheless

for i in seq 1 65535 ; do tcpconnect -v remotehost $i ; done

nmap -T5 -sS -P0 ho.st.ip.addr
That will see what's available port wise on that machine.. Recommend installing cygwin if you are running on windows or don't have access to a linux machine.

softperfect network scanner.

google for it.

I use it alot. Works great

Google for "nmap". I use this all the time. Great for verifying your firewalls are operating as expected too. Plus I believe it was referenced in a Matrix movie which makes it doubly awesome.

You could have the machine send an snmp trap (packet) once a minute to a remote monitor and set up a rule to monitor that you were receiving the trap each minute.

The simple solution to this issue will be to use netcat utility. Only prerequisite for this scenario is that one should be aware of at least one port which is open on that remote machine.

nc -nv ip_address port_number

The above command will give a result, which would determine if the said port is open or not and hence the availability of the machine

Ping is ICMP, if you blocked ICMP you can't ping.

You might still be able to test TCP or UDP ports if you are accepting TCP/UDP connections.

If you are running your test on containers, which lack ping, nc, telnet and other tools, you can use this trick:

(echo >/dev/tcp/$host/$port) &>/dev/null && echo "open" || echo "closed"

This will attempt to connect through tcp/udp through the device (wow, I know) and echo "open" if the port is open or "closed" if it is closed.

It will hang for a while before echoing "close" when that is the case.

You can install a simple web server and use a web page saying "ONLINE".
The you only have to connect to it wherever you want
Of course you need a statin ip or services linke dyndns

A very simple approach is to telnet to a TCP port that should be open on the server, ie:

telnet theServerHostname 80

Although if the service is down you would get the same result as if the host was down.

There are all sorts of scans that can be done with nmap, learn about them on nmap's site and you should become an expert on how to test if a host is up. These include using protocols other than icmp (ping), such as TCP (as telnet does) and UDP.

Also, if you want something that includes the ability to connect to udp, that is similar to telnet in this sense, consider netcat.

Microsoft's own PortQry Command Line Port Scanner Version 2.0

I use it to test SQL Server ports often

open port = LISTENING or NOT LISTENING
firewall = FILTERED