Originally posted here by Surreal
I am indeed using linux. That grep command sounds interesting. What did the command look like?
"grep" and "ngrep" they are differents:
Code:
NAME
       grep,  egrep,  fgrep, zgrep, zegrep, zfgrep, bzgrep, bzegrep, bzfgrep -
       print lines matching a pattern

SYNOPSIS
       grep [options] PATTERN [FILE...]
       grep [options] [-e PATTERN | -f FILE] [FILE...]

DESCRIPTION
       grep searches the named input FILEs (or standard input if no files  are
       named, or the file name - is given) for lines containing a match to the
       given PATTERN.  By default, grep prints the matching lines.

       In addition, two variant programs egrep and fgrep are available.  egrep
       is  the  same  as grep -E.  fgrep is the same as grep -F.  zgrep is the
       same as grep -Z.  zegrep is the same as grep -EZ.  zfgrep is  the  same
       as grep -FZ.
etc
Code:
SYNOPSIS
       ngrep <-hXViwqpevxlDtT> <-IO pcap_dump > < -n num > < -d dev > < -A num
       > < -s snaplen > < match expression > < bpf filter >


DESCRIPTION
       ngrep strives to provide most of GNU grep's common  features,  applying
       them  to the network layer.  ngrep is a pcap-aware tool that will allow
       you to specify extended regular expressions to match against data  pay-
       loads  of  packets.   It  currently recognizes TCP, UDP and ICMP across
       Ethernet, PPP, SLIP, FDDI and null interfaces, and understands bpf fil-
       ter  logic  in  the  same fashion as more common packet sniffing tools,
       such as tcpdump(8) and snoop(1).
etc
So you need to have "ngrep" install on your box and read the manual first..for ngrep and you will know what the command is..