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 or hexadecimal expressions to match
against data payloads of packets. It currently recognizes IPv4/6,
TCP, UDP, ICMPv4/6, IGMP and Raw across Ethernet, PPP, SLIP, FDDI,
Token Ring and null interfaces, and understands BPF filter logic in
the same fashion as more common packet sniffing tools, such as tcpdump
and snoop.

ngrep is built with IPV6 support by default; to disable it, do this:
  NGREP_IPV6=no ./ngrep.SlackBuild

A patch is included for IPV4 and IPV6 packet reassembly applied by
default.  The patch adds the -r switch to ngrep. To disable the patch,
do this:
  ASSEM_PATCH=no ./ngrep.SlackBuild