[Richard Sharpe <sharpe@xxxxxxxxxx>]

I have most of LDP done now, or will soon ... :-)


At 06:28 PM 11/28/00 -0800, Guy Harris wrote:
>> >     I'm trying to code an LDP dissector for Ethereal. LDP uses UDP and
TCP
>> >packets, not raw ones. Can this be done with a dissector? As far as I read
>> >in README.developer, dissectors can only access raw packets. Thanks in
>> >advance.
>> 
>> There are no problems in accessing UDP datagrams and TCP segments within a
>> dissector, see packet-tftp.c and packet-pop.c.
>
>Section "1.4.2 Extracting data from packets" should perhaps be made
>clearer; it says:
>
>	The "tvb" argument to a dissector points to a buffer containing
>	the raw data for the frame.  A tvbuffer is a opaque data
>	structure, the internal data structures are hidden and the data
>	must be access via the tvbuffer accessors.
>
>but what the tvbuff handed to the dissector contains is the raw data for
>the protocol the dissector is handling - the IP dissector is handed a
>tvbuff referring to the link-layer payload, i.e.  the IP datagram
>*without* the link-layer header, the TCP and UDP dissectors get handed a
>tvbuff referring to the IP payload, i.e. the TCP segment or UDP
>datagram *without* the IP header, and dissectors for protocols above TCP
>or UDP get handed a tvbuff referring to the TCP or UDP payload, i.e. the
>data in the TCP segment *without* the TCP header or the data in the UDP
>datagram *without* the UDP header.
>
>> However, what is LDP, apart from the Linux Documentation Project?
>
>As per earlier mail from him:
>
>	From: "Armenio Pinto (EST)" <est-a-pinto@xxxxxxxxxxxxx>
>	To: ethereal-users@xxxxxxxxxxxx
>	Subject: [Ethereal-users] Ethereal Plug-ins.
>	Date: Mon, 27 Nov 2000 13:52:20 -0000
>
>	Hi there,
>
>	     Can anyone please tell me where can I find resources about building
>	Ethereal plug-ins? I'm trying to bring LDP (Label Distribution Protocol)
>	support to Ethereal. Thanks in advance.
>
>	Arménio Pinto - PT Inovação SA, Portugal
>
>it's the Label Distribution Protocol.
>
>I assume the LDP to which he's referring is the one that's part of the
>architecture for "multiprotocol label switching":
>
>	http://www.ietf.org/html.charters/mpls-charter.html
>
>which, at least from a quick look at
>
>	http://www.ietf.org/internet-drafts/draft-ietf-mpls-arch-07.txt
>
>"Multiprotocol Label Switching Architecture", involves attaching labels
>to frames, where the label can be used to refer to data on the next
>router that tells the router where next to send the packet and what
>label to put on it for the edification of that subsequent router (and
>may also contain QoS information).
>
>It sounds as if the idea is to speed up packet switching by storing some
>state information, in routers, about paths through the network for
>packet flows, and letting the routers look up the path information from
>the label rather than having to look up the source and destination IP
>addresses, and other such information, in routing tables.
>
>I seem to remember Cisco discussing a label switching scheme (which I
>think they may have patented) a while ago.
>
>The LDP spec is at
>
>	http://www.ietf.org/internet-drafts/draft-ietf-mpls-ldp-11.txt
>
>and is used to let routers tell each other about paths through the
>network.
>
>_______________________________________________
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>Ethereal-dev@xxxxxxxxxxxx
>http://www.ethereal.com/mailman/listinfo/ethereal-dev
>

Regards
-------
Richard Sharpe, sharpe@xxxxxxxxxx
Samba (Team member, www.samba.org), Ethereal (Team member, www.zing.org)
Contributing author, SAMS Teach Yourself Samba in 24 Hours
Author, Special Edition, Using Samba