NLRI Encoding as per
---------------------

RFC5575 - Dissemination of Flow Specification Rules


Compile package
---------------------
 $ make
 
Run interactive mode
---------------------
 $ ./flospec
 
 waits in the nlri> prompt, type the flow description string and hit <enter>
 In the nlri> prompt, 'show' shows upto 5 previous flow description history
 and the 'compare' command can be used to compare any 2 of them
 use Ctrl-D or type quit to end.

Files:
---------------------
Makefile
README      - this file
README.code - Explanation of Data structures used
TODO        - what can be done better? what more can be added?
encode.c    - encoding macros
flospec.c   - main file; has 2 different interfaces (see below) to encode NLRI 
token.c     - tokeniser for a human readable description of NLRI
bitset.h    - bit set routines (handles all endiannes)
dscp_cp.h   - DSCP code point definitions
utils.c
iana_ip_proto.h - picked up from http://www.iana.org/assignments/protocol-numbers/

Ways to encode flow spec:
------------------------

To test the encoder, the encoding Macros can be used within the code
or the more convenient  readable description can be given in a string form
to the tokeniser which will parse and interpret the NLRI components
and then order them in ascending order and encode. 

To test, the flospec.c creates a interactive program which will read a line
containing the flow description and encodes it, later decodes and displays it
to verify (the decoder dumps data in UPPERCASE).

The Macros needed for encode can be seen in the encode.h and the
flospec.h files and does not need much of an explanation

For interactive flow description, the following are the keywords 

    prefix.dest
    prefix.src
    ip.proto
    port
    port.dest
    port.src
    icmp.type
    icmp.code
    tcp.flags
    pak.len
    dscp
    fragment

and can be combined as follows

   ip.proto = tcp|udp and port.dest >= 300 & <= 600 and tcp.flags = 0x80

Note:
---------------------
   - 'and' is used to seperate the flow components, and within a component
     rule-set, c-style bitwise '|' and  '&' is used to specify more than
     1 value.
   - The comparison operators are again c-style: != >= <= < >, except = (not ==)
   - No new operators are assigned for bitwise op, hence = and != have to 
     be used
   - only commonly used protos are recognised - like 'tcp' 'rsvp' 'icmp' etc

Debugging & understanding
------------------------
set the DEBUG macro in debug.h to a non zero value to see whats
happening under cover.
make clean and re-make before re run.

Quirks:
---------------------
 - Within the values of a component, & (if used) has to appear before |
 - While specifying prefixes, the IP address have to be fully given, i.e,
   10.0.1/24 should be given as 10.0.1.0/24 (limitation of ip_addr() )
 - If length omitted in the above case, it is treated as /32


Examples (from the RFC)
----------------------

nlri> prefix.dest = 10.0.1.0/24 and ip.proto = tcp and port = 25

 Final buf len = 12, data/hdr len = 11 (B)
 0B 01 18 0A 00 01 03 81 06 04 81 19 

 DEST-PREFIX  = 0xA000100/24 
 AND
 IP-PROTO = 0x6 
 AND
 PORT = 0x19 

nlri> prefix.dest = 10.0.1.0/24 and  prefix.src = 192.0.0.0/8 and port >= 137 & <= 139 | = 8080

 Final buf len = 17, data/hdr len = 16 (10)
 10 01 18 0A 00 01 02 08 C0 04 03 89 45 8B 91 1F 90 

 DEST-PREFIX  = 0xA000100/24 
 AND
 SOURCE-PREFIX = 0xC0000000/8 
 AND
 PORT >= 0x89  AND PORT <= 0x8B  OR PORT = 0x1F90 

nlri> show

 [0] : prefix.dest = 10.0.1.0/24 and  prefix.src = 192.0.0.0/8 and port >= 137 & <= 139 | = 8080

 [1] : prefix.dest = 10.0.1.0/24 and ip.proto = tcp and port = 25

nlri> compare 0 1

 Precedence: prefix.dest = 10.0.1.0/24 and ip.proto = tcp and port = 25

nlri>