ok...uhm i want to ask
can ngrep be detected.i mean can admins detect that someone is using ngrep ?
can packets be hidden from ngrep,for example can someone hide all packets from ngrep.
it seems that i am allowed to use ngrep,im not going to go into issues
of legality/illegality(you can discuss this elsewhere,but not in this topic).
also its unclear to me how packets can be printed by ngrep so fast because i know that in
some networks..there are transfers of 4-5mb/s so i cant imagine how ngrep could print them
on the screen that fast,does it skip some of them ?
thank you for any information you may provide

ngrep can see anything reaching your nic. it's impossible to detect. it's impossible to "hide" data from it, but the features of the nic you are using will affect what can be listened for, primarily if it can use promiscuous mode or not. it can only print stuff as fast as the rest of the system can cope with, i assume it has an internal buffer that would fill up if the system isn't accepting data output from it fast enough.

ngrep is just a libpcap application, just like tcpdump, wireshark, tcptrace etc... all sitting on the same common library.

"the features of the nic you are using will affect what can be listened for",so data can be hidden from me right ?

no, just promisc mode, which isn't "hiding" in any way.

ok ill go look elsewhere