Hi,
The pacet capture is handled by libpcap or winpcap (or some other tool/program) 
depending on the platform used.
In the case of Ethernet the capture is made by puting the Ethernet car in 
promiscuous mode
which means that all packets on the network segment the card is on will be 
captured.
 
Dissection is based on the protocol layer an Ethernet packet will be handled to 
the Ethernet dissector
which in the case of IP will hand it to the IP dissector which will hand it to 
the UDP dissector in the case of UDP.
On UDP it gets trickier to discover what protocol is used on top of UDP 
basically three metods exists:
- Dissector registered on a particular port.
- Hueristics ( look at the packet data and guess).
- Conversation - A previous (Control packet) packet was dissected which had 
information about which ports and addresses was going to be used for a certain 
protocol.
 
Its done in a similar manner for other protocols.
 
BR
Anders

________________________________

From: [EMAIL PROTECTED] on behalf of prashanth joshi
Sent: Wed 12/13/2006 4:53 PM
To: Developer support list for Wireshark
Subject: Re: [Wireshark-dev] Protocol development


Hi our requirement is as follows:
The packets are sent from the  application to a particular multicast ip address.
Now we want ethereal to capture these packets from the network.
So as I have observed for the implemnation of a protocol, a dissector has to be 
registered with a port. But I really dont know how they are getting the packets 
capturing at the ip layer. I mean I dont know how ethereal recognizes the ip 
address on which it has to capture the ip packets. Pleaseb any one tell me how 
this can be done. Besos we are supposed to implement our protocol for a 
particular multicast address and a particular udp port.
Regards
Prashanth

[EMAIL PROTECTED] wrote:

        Hi,
        
        You can't as you said "register a protocol for an IP address" ... but 
you can
        register a plugin which will dissect your protocol.
        If you only want the dissection for a particular IP address, wireshark 
allows
        you to create a filter (capture or display).
        
        for a plugin implementation in wireshark see the documentation
        http://www.wireshark.org/docs/wsdg_html_chunked/
        
        Regards,
        Sebastien Tandel
        
        Selon prashanth joshi :
        
        > Hi all,
        > We are required to develop a protocol on ethereal. The packets are 
sent to
        > a particular ip address and the ethereal is supposed to capture 
packets from
        > that ip address. Please any one tell me how to register our protocol 
for that
        > ip address.
        > Regards,
        > Prashanth.
        >
        >
        > ---------------------------------
        > Everyone is raving about the all-new Yahoo! Mail beta.
        
        
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