Internet Engineering Task Force                           Nevil Brownlee
INTERNET-DRAFT                                The University of Auckland
                                                   Expires October November 1999

              SRL: A Language for Describing Traffic Flows
                and Specifying Actions forFlow for Flow Groups

               <draft-ietf-rtfm-ruleset-language-04.txt>

               <draft-ietf-rtfm-ruleset-language-05.txt>

Status of this Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

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This Internet Draft is a product of the Realtime Traffic Flow
Measurement Working Group of the IETF.

Abstract

This document describes a language for specifying rulesets, i.e.
configuration files which may be loaded into a traffic flow meter so as
to specify which traffic flows are measured by the meter, and the
information it will store for each flow.

Contents

 1 Purpose and Scope                                                   3
   1.1 RTFM Meters and Traffic Flows  . . . . . . . . . . . . . . . .  3
   1.2 SRL Overview . . . . . . . . . . . . . . . . . . . . . . . . .  4

 2 SRL Language Description                                            5
   2.1 Define Directive . . . . . . . . . . . . . . . . . . . . . . .  5
   2.2 Program  . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   2.3 Declaration  . . . . . . . . . . . . . . . . . . . . . . . . .  6

 3 Statement                                                           6
   3.1 IF_statement . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.1 expression . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.2 term . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.3 factor . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.4 operand_list . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.5 operand  . . . . . . . . . . . . . . . . . . . . . . . . .  8
     3.1.6 Test Part  . . . . . . . . . . . . . . . . . . . . . . . .  8
     3.1.7 Action Part  . . . . . . . . . . . . . . . . . . . . . . .  9
     3.1.8 ELSE Clause  . . . . . . . . . . . . . . . . . . . . . . .  9
   3.2 Compound_statement . . . . . . . . . . . . . . . . . . . . . .  9
   3.3 Imperative_statement . . . . . . . . . . . . . . . . . . . . . 10
     3.3.1 SAVE Statement . . . . . . . . . . . . . . . . . . . . . . 10
     3.3.2 COUNT Statement  . . . . . . . . . . . . . . . . . . . . . 11
     3.3.3 EXIT Statement . . . . . . . . . . . . . . . . . . . . . . 11
     3.3.4 IGNORE Statement . . . . . . . . . . . . . . . . . . . . . 12
     3.3.5 NOMATCH Statement  . . . . . . . . . . . . . . . . . . . . 12
     3.3.6 STORE Statement  . . . . . . . . . . . . . . . . . . . . . 12
     3.3.7 RETURN Statement . . . . . . . . . . . . . . . . . . . . . 12
   3.4 Subroutine_declaration . . . . . . . . . . . . . . . . . . . . 13
   3.5 CALL_statement . . . . . . . . . . . . . . . . . . . . . . . . 13

 4 Example Programs                                                   14
   4.1 Classify IP Port Numbers . . . . . . . . . . . . . . . . . . . 14
   4.2 Classify Traffic into Groups of Networks . . . . . . . . . . . 15

 5 IANA Considerations                                                16

 6 APPENDICES                                                         17
   6.1 Appendix A: SRL Syntax in BNF  . . . . . . . . . . . . . . . . 17
   6.2 Appendix B: Syntax for Values and Masks  . . . . . . . . . . . 19
   6.3 Appendix C: RTFM Attribute Information . . . . . . . . . . . . 19

 7 Acknowledgments                                                    21

 8 References                                                         21

 9 Author's Address                                                   21

1 Purpose and Scope

A ruleset for an RTFM Meter is a sequence of instructions to be executed
by the meter's Pattern Matching Engine (PME). The form of these
instructions is described in detail in the 'RTFM Architecture' and 'RTFM
Meter MIB' documents [1], [2], but most users - at least initially -
find them confusing and difficult to write, mainly because the effect of
each instruction is strongly dependent on the state of the meter's
Packet Matching Engine at the moment of its execution.

SRL (the Simple Ruleset Language) is a procedural language for creating
RTFM rulesets.  It has been designed to be simple for people to
understand, using statements which help to clarify the execution context
in which they operate.  SRL programs will be compiled into rulesets
which can then be downloaded to RTFM meters.

An SRL compiler is available as part of NeTraMet (a free-software
implementation of the RTFM meter and manager), version 4.2 [3].

1.1 RTFM Meters and Traffic Flows

The RTFM Architecture [1] defines a set of 'attributes' which apply to
network traffic.  Among the attributes are 'address attributes,' such as
PeerType, PeerAddress, TransType and TransAddress, which have meaning
for many protocols, e.g. for IP traffic (PeerType == IP) PeerAddress is
an IP address, TransType is TCP, UDP, ICMP, etc., and TransAddress is
usually an IP port number.

An 'RTFM Traffic Flow' is simply a stream of packets observed by a meter
as they pass across a network between two end points (or to/from a
single end point).  Each 'end point' of a flow is specified by the set
of values of its address attributes.

An 'RTFM Meter' is a measuring device - e.g. a program running on a
Unix or PC host - which observes passing packets and builds 'Flow Data
Records' for the flows of interest.

RTFM traffic flows have another important property - they are
bi-directional.  This means that each flow data record in the meter has
two sets of counters, one for packets travelling from source to
destination, the other for returning packets.  Within the RTFM
architecture such counters appear as further attributes of the flow.

An RTFM meter must be configured by the user, which means creating a
'Ruleset' so as to specify which flows are to be measured, and how much
information (i.e. which attributes) should be stored for each of them.
A ruleset is effectively a program for a minimal virtual machine, the
'Packet Matching Engine (PME),' which is described in detail in [1].  An
RTFM meter may run multiple rule sets, with every passing packet being
processed by each of the rulesets.  The rule 'actions' in this document
are described as though only a single ruleset were running.

In the past creating a ruleset has meant writing machine code for the
PME, which has proved rather difficult to do.  SRL provides a high-level
language which should enable users to create effective rulesets without
having to understand the details of the PME.

The language may be useful in other applications, being suitable for any
application area which involves selecting traffic flows from a stream of
packets.

1.2 SRL Overview

An SRL program is executed from the beginning for each new packet
arriving at the meter.  It has two essential goals.

 (a) Decide whether the current packet is part of a flow which is of
     interest and, if necessary, determine its direction (i.e. decide
     which of its end-points is considered to be its source).  Other
     packets will be ignored.

 (b) SAVE whatever information is required to identify the flow and
     accumulate (COUNT) quantitative information for that flow.

At execution, the meter's Packet Matching Engine (PME) begins by using
source and destination attributes as they appear 'on the wire.'  If the
attributes do not match those of a flow to be recorded, the PME will
normally execute the program again, this time with the source and
destination addresses interchanged.  Because of this bi-directional
matching, an RTFM meter is able to build up tables of flows with two
sets of counters - one for forward packets, the other for backward
packets.  The programmer can, if required, suppress the
reverse-direction matching and assign 'forward' and 'backward'
directions which conform to the conventions of the external context.

Goal (a) is achieved using IF statements which perform comparisons on
information from the packet or from SRL variables.  Goal (b) is achieved

using one or more SAVE statements to store the flow's identification
attributes; a COUNT statement then increments the statistical data
accumulating for it.

2 SRL Language Description

The SRL language is explained below using 'railway diagrams' to describe
the syntax.  Flow through a diagram is from left to right.  The only
exception to this is that lines carrying a left arrow may only be
traversed right to left.  In the diagrams, keywords are written in
capital letters; in practice an SRL compiler must be insensitive to
case.  Lower-case identifiers are explained in the text, or they refer
to another diagram.

The tokens of an SRL program obey the following rules:

  - Comments may appear on any line of an SRL program, following a #
  - White space is used to separate tokens
  - Semicolon is used as the terminator for most statements
  - Identifiers (e.g. for defines and labels) must start with a letter
  - Identifiers may contain letters, digits and underscores
  - The case of letters is not significant
  - Reserved words (shown in upper case in this documents)
       may not be used as identifiers

2.1 Define Directive

  --- DEFINE -- defname ---- = ---- defined_text ------------------ ;

Simple parameterless defines are supported via the syntax above.  The
define name, defname, is an identifier.  The defined text starts after
the equal sign, and continues up to (but not including) the closing
semicolon.  If a semicolon is required within the defined text it must
be preceded by a backslash, i.e. \; in an SRL define produces ; in the
text.

Wherever defname appears elsewhere in the program, it will be replaced
by the defined text.

For example,

   DEFINE ftp = (20, 21);
   DEFINE telnet = 23;
   DEFINE www = 80;

2.2 Program

  ------------+-------+-------- Statement -------+-------+-----------
              |       |                          |       |
              |       +------- Declaration ------+       |
              |                                          |
              +---------------------<--------------------+

An SRL program is a sequence of statements or declarations.  It does not
have any special enclosing symbols.  Statements and declarations
terminate with a semicolon, except for compound statements, which
terminate with a right brace.

2.3 Declaration

  ---------------------- Subroutine_declaration ---------------------

SRL's only explicit declaration is the subroutine declaration.  Other
implicit declarations are labels (declared where they appear in front of
a statement) and subroutine parameters (declared in the subroutine
header).

3 Statement

  ----------------+---- IF_statement ----------------+---------------
                  |                                  |
                  +---- Compound_statement ----------+
                  |                                  |
                  +---- Imperative_statement --------+
                  |                                  |
                  +---- CALL_statement --------------+

An SRL program is a sequence of SRL statements.  There are four kinds of
statements, as follows.

3.1 IF_statement

              Test Part                Action Part
            .............            ...............

  --- IF --- expression ---+------------+---- Statement ----+--->
                           |            |                   |
                           +-- SAVE , --+                   |
                           |                                |
                           +-- SAVE ; ----------------------+

         >-----------+-----------------------------+-----------------
                     |                             |
                     +-----ELSE --- Statement -----+

3.1.1 expression

  -------- term --------+------------------------+-------------------
                        |                        |
                        +--<-- term ----- || ----+    logical OR

3.1.2 term

  ------- factor -------+------------------------+-------------------
                        |                        |
                        +--<-- factor --- && ----+    logical AND

3.1.3 factor

  ------------+-------- attrib  ==  operand_list --------+-----------
              |                                          |
              +------------ ( expression ) --------------+

3.1.4 operand_list

  ----------+------------------ operand -----------------+-----------
            |                                            |
            +-- ( operand ---+-------------------+-- ) --+
                             |                   |
                             +-<-- operand  , ---+

3.1.5 operand

  ------------- value ---------+----------------------+--------------
                               |                      |
                               +------- / width ------+
                               |                      |
                               +------- & mask -------+

3.1.6 Test Part

The IF statement evaluates a logical expression.  If the expression
value is TRUE, the action indicated in the 'Action Part' of the diagram
is executed.  If the value is FALSE and the IF has an ELSE clause, that
ELSE clause is executed (see below).

The simplest form of expression is a test for equality (== operator); in
this an RTFM attribute value (from the packet or from an SRL variable)
is ANDed with a mask and compared with a value.  A list of RTFM
attributes is given in Appendix C. More complicated expressions may be
built up using parentheses and the && (logical AND) and || (logical OR)
operators.

Operand values may be specified as dotted decimal, hexadecimal or as a
character constant (enclosed in apostrophes).  The syntax for operand
values is given in Appendix B.

Masks may be specified as numbers,
        dotted decimal  e.g. &255.255
     or hexadecimal     e.g. &FF-FF
or as a width in bits   e.g. /16

If a mask is not specified, an all-ones mask is used.

In SRL a value is always combined with a mask; this combination is
referred to as an operand.  For example, if we were interested in flows
originating from IP network 130.216, we might write:

   IF SourcePeerAddress == 130.216.0.0 & 255.255.0.0  SAVE;

or equivalently

   IF SourcePeerAddress == 130.216/16  SAVE;

A list of values enclosed in parentheses may also be specified; the test
succeeds if the masked attribute equals any of the values in the list.
For example

   IF SourcePeerAddress == ( 130.216.7/24, 130.216.34/24 ) SAVE;

As this last example indicates, values are right-padded with zeroes,
i.e. the given numbers specify the leading bytes of masks and values.

The operand values and masks used in an IF statement must be consistent
with the attribute being tested.  For example, a four-byte value is
acceptable as a peer address, but would not be accepted as a transport
address (which may not be longer than two bytes).

3.1.7 Action Part

A SAVE action (i.e. SAVE , or SAVE ;) saves attribute(s), mask(s) and
value(s) as given in the statement.  If the IF expression tests more
than one attribute, the masks and values are saved for all the matched
attributes.  For each value_list in the statement the value saved is the
one which the packet actually matched.  See below for further
description of SAVE statements.

Other actions are described in detail under "Imperative statements"
below.  Note that the RETURN action is valid only within subroutines.

3.1.8 ELSE Clause

An ELSE Clause provides a statement which will be executed if the IF's
test fails.  The statement following ELSE will often be another IF
statement, providing SRL's version of a 'select' statement.  Note that
an ELSE clause always matches the immediately preceding IF.

3.2 Compound_statement

  -------+-------------+----- { ---+---- Statement ----+--- } -------
         |             |           |                   |
         +-- label : --+           +--------<----------+

A compound statement is a sequence of statements enclosed in braces.
Each statement will terminate with a semicolon, unless it is another
compound statement (which terminates with a right brace).

A compound statement may be labelled, i.e. preceded by an identifier
followed by a semi-colon.  Each statement inside the braces is executed
in sequence unless an EXIT statement is performed, as explained below.

Labels have a well-defined scope, within which they must be unique.
Labels within a subroutine (i.e. between a SUBROUTINE and its matching
ENDSUB) are local to that subroutine and are not visible outside it.
Labels outside subroutines are part of a program's outer block.

3.3 Imperative_statement

  ------+---------------------------------------------------+------ ;
        |                                                   |
        +-- SAVE attrib --+--+-----------+--+---------------+
        |                 |  |           |  |               |
        |                 |  +- / width -+  |               |
        |                 |  |           |  |               |
        |                 |  +- & mask --+  |               |
        |                 |                 |               |
        |                 +--- = operand ---+               |
        |                                                   |
        +-- COUNT ------------------------------------------+
        |                                                   |
        +-- EXIT label  ------------------------------------+
        |                                                   |
        +-- IGNORE -----------------------------------------+
        |                                                   |
        +-- NOMATCH ----------------------------------------+
        |                                                   |
        +-- RETURN --+-------+------------------------------+
        |            |       |                              |
        |            +-- n --+                              |
        |                                                   |
        +-- STORE variable := value ------------------------+

3.3.1 SAVE Statement

The SAVE statement saves information which will (later) identify the
flow in the meter's flow table.  It does not actually record anything in
the table; this is done when a subsequent COUNT statement executes.

SAVE has two possible forms:

   SAVE attrib = operand ;
        saves the attribute, mask and value as given in the statement.
        This form of the SAVE statement is similar to that allowed
        in an IF statement, except that - since imperative statements
        do not perform a test - you may save an arbitrary value.

   SAVE attrib ;
   SAVE attrib / width ;
   SAVE attrib & mask ;
        saves the attribute and mask from the statement, and the
        value resulting from their application to the current packet.
        This is most useful when used to save a value with a wider
        mask than than was used to select the packet.  For example

                IF DestPeerAddress == 130.216/16
                        NOMATCH;
                ELSE IF SourcePeerAddress == 130.216/16 {
                        SAVE SourcePeerAddress /24;
                        COUNT;
                        }
                ELSE IGNORE;

3.3.2 COUNT Statement

The COUNT statement appears after all testing and saving is complete; it
instructs the PME to build the flow identifier from the attributes which
have been SAVEd, find it in the meter's flow table (creating a new entry
if this is the first packet observed for the flow), and increment its
counters.  The meter then moves on to examine the next incoming packet.

3.3.3 EXIT Statement

The EXIT statement exits a labelled compound statement.  The next
statement to be executed will be the one following that compound
statement.  This provides a well-defined way to jump to a clearly
identified point in a program.  For example

   outer: {
      ...
      if SourcePeerAddress == 192.168/16
         exit outer;  # exits the statement labelled 'outer'
      ...
      }
   # execution resumes here

In practice the language provides sufficient logical structure that one
seldom - if ever - needs to use the EXIT statement.

3.3.4 IGNORE Statement

The IGNORE statement terminates examination of the current packet
without saving any information from it.  The meter then moves on to
examine the next incoming packet, beginning again at the first statement
of its program.

3.3.5 NOMATCH Statement

The NOMATCH statement indicates that matching has failed for this
execution of the program.  If it is executed when a packet is being
processed with its addresses in 'on the wire' order, the PME will
perform the program again from the beginning with source and destination
addresses interchanged.  If it is executed following such an
interchange, the packet will be IGNOREd.

NOMATCH is illustrated in the SAVE example (section 3.3.1), where it is
used to ensure that flows having 130.216/16 as an end-point are counted
as though 130.216 had been those flows' source peer (IP) address.

3.3.6 STORE Statement

The STORE statement assigns a value to an SRL variable and SAVEs it.
There are six SRL variables:

           SourceClass        SourceKind
           DestClass          DestKind
           FlowClass          FlowKind

Their names have no particular significance; they were arbitrarily
chosen as likely RTFM attributes but can be used to store any
single-byte integer values.  Their values are set to zero each time
examination of a new packet begins.  For example

   STORE SourceClass := 3;
   STORE FlowKind := 'W'

3.3.7 RETURN Statement

The RETURN statement is used to return from subroutines and can be used
only within the context of a subroutine.  It is described in detail
below (CALL statement).

3.4 Subroutine_declaration

  -- SUBROUTINE subname ( --+-----------------------------+-- ) -->
                            |                             |
                            +--+-- ADDRESS --- pname --+--+
                               |                       |
                               +-- VARIABLE -- pname --+
                               |                       |
                               +------<------- , ------+

         >------+-------- Statement ---------+----- ENDSUB -------- ;
                |                            |
                +-------------<--------------+

A Subroutine declaration has three parts:

   the subname is an identifier, used to name the subroutine.

   the parameter list specifies the subroutine's parameters.
      Each parameter is preceded with a keyword indicating its
      type - VARIABLE indicates an SRL variable (see the STORE
      statement above), ADDRESS indicates any other RTFM attribute.
      A parameter name may be any identifier, and its scope is
      limited to the subroutine's body.

   the body specifies what processing the subroutine will perform.
      This is simply a sequence of Statements, terminated by the
      ENDSUB keyword.

Note that EXITs in a subroutine may not refer to labels outside it.  The
only way to leave a subroutine is via a RETURN statement.

3.5 CALL_statement

  ---- CALL subname ( --+---------------------+-- ) ---->
                        |                     |
                        +--+-- parameter --+--+
                           |               |
                           +----<--- , ----+
        >---+-------------------------------------+--- ENDCALL ---- ;
            |                                     |
            +---+--+-- n : --+--- Statement --+---+
                |  |         |                |
                |  +----<----+                |
                |                             |
                +--------------<--------------+

The CALL statement invokes an SRL subroutine.  The parameters are SRL
variables or other RTFM attributes, and their types must match those in
the subroutine declaration.  Following the parameters is a sequence of
statements, each preceded by an integer label.  These labels will
normally be 1:, 2:, 3:, etc, but they do not have to be contiguous, nor
in any particular order.  They are referred to in RETURN statements
within the subroutine body.

    e.g. RETURN 2;   would return to the statement labelled 2:
                        within in the CALL statement.

Execution of the labelled statement completes the CALL.

If the return statement does not specify a return label, the first
statement executed after RETURN will be the statement immediately
following ENDCALL.

4 Example Programs

4.1 Classify IP Port Numbers

#
#  Classify IP port numbers
#
   if SourcePeerType == IP save;
   else ignore;  # Not an IP packet
#
   if SourceTransAddress == (www, ftp, telnet)  nomatch;
      # We want the well-known port as Dest
#
   if DestTransAddress == telnet
      save, store FlowKind := 'T';
   else if DestTransAddress == www
      save, store FlowKind := 'W';
   else if DestTransAddress == ftp
      save, store FlowKind := 'F';
   else {
      save DestTransAddress;
      store FlowKind := '?';
      }
   save SourcePeerAddress /32;
   save DestPeerAddress   /32;
   count;
#

This program counts only IP packets, saving SourceTransType (tcp, udp or
0), Source- and DestPeerAddress (32-bit IP addresses) and FlowKind ('W'
for www, 'F' for ftp, 'T' for telnet, '?'  for unclassified).  The
program uses a NOMATCH action to specify the packet direction - its
resulting flows will have the well-known ports as their destination.

4.2 Classify Traffic into Groups of Networks

#
# SRL program to classify traffic into network groups
#
define my_net = 130.216/16;
define k_nets = ( 130.217/16, 130.123/16, 130.195/16,
                 132.181/16, 138.75/16, 139.80/16 );
#
   call net_kind (SourcePeerAddress, SourceKind)
      endcall;
   call net_kind (DestPeerAddress,   DestKind)
      endcall;
   count;
#
   subroutine net_kind (address addr, variable net)
      if addr == my_net save, {
         store net := 10;  return 1;
         }
      else if addr == k_nets save, {
         store net := 20;  return 2;
         }
      save addr/24;  # Not my_net or in k_nets
      store net := 30;  return 3;
      endsub;
#

The net_kind subroutine determines whether addr is my network (130.216),
one of the Kawaihiko networks (in the k_nets list), or some other

network.  It saves the network address from addr (16 bits for my_net and
the k_net networks, 24 bits for others), stores a value of 10, 20 or 30
in net, and returns to 1:, 2:  or 3:.  Note that the network numbers
used are contained within the two DEFINEs, making them easy to change.

net_kind is called twice, saving Source- and DestPeerAddress and Source-
and DestKind; the COUNT statement produces flows identified by these
four RTFM attributes, with no particular source-dest ordering.

In the program no use is made of return numbers and they could have been
omitted.  However, we might wish to re-use the subroutine in another
program doing different things for different return numbers, as in the
version below.

   call net_kind (DestPeerAddress, DestKind)
      1: nomatch;  # We want my_net as source
         endcall;
   call net_kind (SourcePeerAddress, SourceKind)
      1: count;    # my_net -> other networks
         endcall;
   save SourcePeerAddress /24;
   save DestPeerAddress /24;
   count;

This version uses a NOMATCH statement to ensure that its resulting flows
have my_net as their source.  The NOMATCH also rejects my_net -> my_net
traffic.  Traffic which doesn't have my_net as source or destination
saves 24 bits of its peer addresses (the subroutine might only have
saved 16) before counting such an unusual flow.

5 IANA Considerations

Appendix C below lists the RTFM attributes by name.  Since SRL only
refers to attributes by name, SRL users do not have to know the
attribute numbers.

The size (in bytes) of the various attribute values is also listed in
Appendix C. These sizes reflect the object sizes for the attribute
values as they are stored in the RTFM Meter MIB [2].

IANA considerations for allocating new attributes are discussed in
detail in the RTFM Architecture document [1].

6 APPENDICES

6.1 Appendix A: SRL Syntax in BNF

   <SRL program>    ::=  <S or D> | <SRL program> <S or D>

   <S or D>         ::=  <statement> | <declaration>

   <declaration>    ::=  <Subroutine declaration>

   <statement>      ::=  <IF statement> |
                         <Compound statement> |
                         <Imperative statement> |
                         <CALL statement>

   <IF statement>   ::=  IF <expression> <if action> <opt else>

   <if action>      ::=  SAVE ; |
                         SAVE , <statement> |
                         <statement>

   <opt else>       ::=  <null> |
                         ELSE <statement>

   <expression>     ::=  <term> | <term> || <term>

   <term>           ::=  <factor> | <factor> && <factor>

   <factor>         ::=  <attribute> == <operand list> |
                         ( <expression> )

   <operand list>   ::=  <operand> | ( <actual operand list> )

   <actual operand list> ::= <operand> |
                         <actual operand list> , <operand>

   <operand>        ::=  <value> |
                         <value> / <width> |
                         <value> & <mask>

   <Compound statement> ::= <opt label> { <statement seq> }

   <opt label>      ::=  <null> |
                         <identifier> :

   <statement seq>  ::=  <statement> | <statement seq> <statement>
   <Imperative statement> ::=  ; |
                         SAVE <attribute> <opt operand> ; |
                         COUNT ; |
                         EXIT <label> ; |
                         IGNORE ; |
                         NOMATCH ; |
                         RETURN <integer> ; |
                         RETURN ; |
                         STORE <variable> := <value> ;

   <opt operand>    ::=  <null> |
                         <width or mask> |
                         = <operand>

   <width or mask>   ::= / <width> | & <mask>

   <Subroutine declaration> ::=
                         SUBROUTINE <sub header> <sub body> ENDSUB ;

   <sub header>     ::=  <subname> ( ) |
                         <subname> ( <sub param list> )

   <sub param list> ::= <sub param> | <sub param list> , <sub param>

   <sub param>      ::=  ADDRESS <pname> | VARIABLE <pname>

   <pname>          ::=  <identifier>

   <sub body>       ::=  <statement sequence>

   <CALL statement> ::=  CALL <call header> <opt call body> ENDCALL ;

   <call header>    ::=  <subname> ( ) |
                         <subname> ( <call param list> )

   <call param list> ::= <call param> |
                         <call param list> , <call param>

   <call param>     ::=  <attribute> | <variable>

   <opt call body>  ::=  <null> |
                         <actual call body>

   <actual call body> ::=  <numbered statement> |
                         <actual call body> <numbered statement>

   <numbered statement> ::= <int label seq> <statement>

   <int label seq>  ::=  <integer> : | <int label seq> <integer> :

The following are terminals, recognised by the scanner:

   <identifier>     Described in section 2
   <integer>        A decimal integer

   <attribute>      Attribute name, as listed in Appendix C

   <value>, <mask>  Described in section 5.2

   <width>     ::= <integer>
   <label>     ::= <identifier>

   <variable>  ::=  SourceClass _ DestClass _ FlowClass _
                       SourceKind _ DestKind _ FlowKind

6.2 Appendix B: Syntax for Values and Masks

Values and masks consist of sequences of numeric fields, each of one or
more bytes.  The non-blank character following a field indicates the
field width, and whether the number is decimal or hexadecimal.  These
'field type' characters may be:

   .  period      decimal, single byte
   -  minus       hex,     single byte
   !  exclaim     decimal, two bytes

For example, 130.216.0.0 is an IP address (in dotted decimal), and
FF-FF-00-00 is an IP address in hexadecimal.

The last field of a value or mask has no field width character.  Instead
it takes the same width as the preceding field.  For example, 1.3.10!50
and 1.3.0.10.0.50 are two different ways to specify the same value.

Unspecified fields (at the right-hand side of a value or mask) are set
to zero, i.e. 130.216 is the same as 130.216.0.0.

If only a single field is specified (no field width character), the
value given fills the whole field.  For example, 23 and 0.23 specify the
same value for a SourceTransAddress operand.  For variables (which have
one-byte values) a C-style character constant may also be used.

In addition, addresses and masks may also use the conventions set
out in the IP Version 6 Addressing Architecture RFC [4].

6.3 Appendix C: RTFM Attribute Information

The following attributes may be tested in an IF statement, and their
values may be SAVEd (except for MatchingStoD). Their size (in bytes) is
shown to the left, and a brief description is given for each.

  1  SourceInterface, DestInterface
        Interface(s) on which the flow was observed

  1  SourceAdjacentType, DestAdjacentType
        Indicates the interface type(s)

  6  SourceAdjacentAddress, DestAdjacentAddress
        For IEEE 802.x interfaces, the MAC addresses for the flow

  1  SourcePeerType, DestPeerType
        Peer protocol types, e.g. IPv4, Novell, Ethertalk, ..

  4  SourcePeerAddress, DestPeerAddress
        Peer Addresses (size varies, e.g. 4 for IPv4, 3 for Ethertalk))

  1  SourceTransType, DestTransType
        Transport layer type, e.g TCP, UDP, IS-IS

  2  SourceTransAddress, DestTransAddress
        Transport layer addresses (port numbers for TCP and UDP)

  1  FlowRuleset
        Rule set number for the flow

  1  MatchingStoD
        Indicates whether the packet is being matched with its
        addresses in 'wire order.'  See reference [1] for details.

The following variables may be tested in an IF, and their values may be
set by a STORE. They all have one-byte values.

     SourceClass, DestClass, FlowClass,
     SourceKind,  DestKind,  FlowKind

The following RTFM attributes are not address attributes - they are
measured attributes of a flow.  Their values may be read from an RTFM
meter.  (For example, NeTraMet uses a FORMAT statement to specify which
attribute values are to be read from the meter.)

  8  ToOctets, FromOctets
        Total number of octets seen for each direction of the flow
  8  ToPDUs, FromPDUs
        Total number of PDUs seen for each direction of the flow

  4  FirstTime, LastTime
        Time (in centiseconds) that first and last PDUs were seen
        for the flow

Other attributes will be defined by the RTFM working group from time to
time.

7 Acknowledgments

The SRL language is part of the RTFM Working Group's efforts to make the
RTFM traffic measurement system easier to use.  Initial work on the
language was done by Cyndi Mills and Brad Frazee in Boston.  SRL was
developed in Auckland; it was greatly assisted by detailed discussion
with John White and Russell Fulton.  Discussion has continued on the
RTFM and NeTraMet mailing lists.

8 References

    [1] Brownlee, N., Mills, C., and G. Ruth, "Traffic Flow
    Measurement:  Architecture", RFC 2063, The University of
    Auckland, GTE Laboratories, Inc, January 1997.

    [2] Brownlee, N., "Traffic Flow Measurement:  Meter MIB", RFC
    2064, The University of Auckland, January 1997.

    [3] Brownlee, N., NeTraMet home page,
    http://www.auckland.ac.nz/net/NeTraMet

    [4] Hinden, R., and Deering, S., "IP Version 6 Addressing
    Architecture", RFC 2373, Nokia, Cisco Systems, July 1998.

9 Author's Address

    Nevil Brownlee
    Information Technology Systems & Services
    The University of Auckland

    Phone: +64 9 373 7599 x8941
    E-mail: n.brownlee@auckland.ac.nz

                                                  Expires October November 1999