Luk� Oliva wrote:
Hello to the community,
I am doing some testing for the Diameter protocol and I noticed
interesting behaviour of the display filters. I noticed that if I run
tshark -r mypcap.pcap -R "diameter.cmd.code==302"
then the output contains afterwards also Diameter packets with
different diameter.cmd.code. I am not sure if it is actually a bug and
how tshark handles this filtering for application protocols.
E.g.: If there is a packet on containing more Diameter (or other
application protocol) messages on IP (or possibly TCP) level, how is
this will the display filter filter all of them?
Just for the illustration:
1 TCP packet: Diameter message 1 (LIR), Diameter message 2 (MAR),
Diameter message 3 (SAR)
Running tshark -r mypcap.pcap -R "diameter.cmd.code==302" ... # so
filtering out the LIR messages which have message code 302
Should the tshark produce a list of LIR messages only?
This is normal behavior. The read/display you have above means:
There exists a field named "diameter.cmd.code" with the value 302 in
this *frame*.
If the frame passes that filter, it is displayed.
In other words, while Wireshark's TCP dissector is capable of handling
multiple upper-layer messages in a given frame, the underlying
architecture is still frame-based.
(You'll see this a lot with SCTP chunk bundling too.)
