File: rfc2723.txt

package info (click to toggle)
doc-rfc 20181229-2
  • links: PTS, VCS
  • area: non-free
  • in suites: buster
  • size: 570,944 kB
  • sloc: xml: 285,646; sh: 107; python: 90; perl: 42; makefile: 14
file content (1235 lines) | stat: -rw-r--r-- 44,406 bytes parent folder | download | duplicates (5)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235






Network Working Group                                        N. Brownlee
Request for Comments: 2723                    The University of Auckland
Category: Informational                                     October 1999


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

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

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.

Table of Contents

   1  Purpose and Scope . . . . . . . . . . . . . . . . . . . . . .    2
      1.1 RTFM Meters and Traffic Flows . . . . . . . . . . . . . .    2
      1.2 SRL Overview  . . . . . . . . . . . . . . . . . . . . . .    3
   2  SRL Language Description  . . . . . . . . . . . . . . . . . .    4
      2.1 Define Directive  . . . . . . . . . . . . . . . . . . . .    4
      2.2 Program . . . . . . . . . . . . . . . . . . . . . . . . .    5
      2.3 Declaration . . . . . . . . . . . . . . . . . . . . . . .    5
   3  Statement . . . . . . . . . . . . . . . . . . . . . . . . . .    5
      3.1 IF_statement  . . . . . . . . . . . . . . . . . . . . . .    6
          3.1.1 expression  . . . . . . . . . . . . . . . . . . . .    6
          3.1.2 term  . . . . . . . . . . . . . . . . . . . . . . .    6
          3.1.3 factor  . . . . . . . . . . . . . . . . . . . . . .    6
          3.1.4 operand_list  . . . . . . . . . . . . . . . . . . .    6
          3.1.5 operand . . . . . . . . . . . . . . . . . . . . . .    6
          3.1.6 Test Part . . . . . . . . . . . . . . . . . . . . .    7
          3.1.7 Action Part . . . . . . . . . . . . . . . . . . . .    8
          3.1.8 ELSE Clause . . . . . . . . . . . . . . . . . . . .    8
      3.2 Compound_statement  . . . . . . . . . . . . . . . . . . .    8
      3.3 Imperative_statement  . . . . . . . . . . . . . . . . . .    9
          3.3.1 SAVE Statement  . . . . . . . . . . . . . . . . . .    9
          3.3.2 COUNT Statement . . . . . . . . . . . . . . . . . .   10



Brownlee                     Informational                      [Page 1]

RFC 2723              SRL: A Traffic Flow Language          October 1999


          3.3.3 EXIT Statement  . . . . . . . . . . . . . . . . . .   10
          3.3.4 IGNORE Statement  . . . . . . . . . . . . . . . . .   10
          3.3.5 NOMATCH Statement . . . . . . . . . . . . . . . . .   10
          3.3.6 STORE Statement . . . . . . . . . . . . . . . . . .   11
          3.3.7 RETURN Statement  . . . . . . . . . . . . . . . . .   11
      3.4 Subroutine_declaration  . . . . . . . . . . . . . . . . .   11
      3.5 CALL_statement  . . . . . . . . . . . . . . . . . . . . .   12
   4  Example Programs  . . . . . . . . . . . . . . . . . . . . . .   13
      4.1 Classify IP Port Numbers  . . . . . . . . . . . . . . . .   13
      4.2 Classify Traffic into Groups of Networks  . . . . . . . .   14
   5  Security Considerations . . . . . . . . . . . . . . . . . . .   15
   6  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   15
   7  APPENDICES  . . . . . . . . . . . . . . . . . . . . . . . . .   16
      7.1 Appendix A: SRL Syntax in BNF . . . . . . . . . . . . . .   16
      7.2 Appendix B: Syntax for Values and Masks . . . . . . . . .   18
      7.3 Appendix C: RTFM Attribute Information  . . . . . . . . .   19
   8  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   20
   9  References  . . . . . . . . . . . . . . . . . . . . . . . . .   20
   10 Author's Address  . . . . . . . . . . . . . . . . . . . . . .   21
   11 Full Copyright Statement  . . . . . . . . . . . . . . . . . .   22

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 [RTFM-ARC, RTFM-MIB], 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
   [NETRAMET].

1.1  RTFM Meters and Traffic Flows

   The RTFM Architecture [RTFM-ARC] 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 IPv4



Brownlee                     Informational                      [Page 2]

RFC 2723              SRL: A Traffic Flow Language          October 1999


   traffic (PeerType == 1) PeerAddress is an IP address, TransType is
   TCP(6), UDP(17), ICMP(1), 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 [RTFM-ARC]. 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.




Brownlee                     Informational                      [Page 3]

RFC 2723              SRL: A Traffic Flow Language          October 1999


   (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 document) 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



Brownlee                     Informational                      [Page 4]

RFC 2723              SRL: A Traffic Flow Language          October 1999


   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);  # Well-known Port numbers from [ASG-NBR]
   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.




Brownlee                     Informational                      [Page 5]

RFC 2723              SRL: A Traffic Flow Language          October 1999


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 -------+



Brownlee                     Informational                      [Page 6]

RFC 2723              SRL: A Traffic Flow Language          October 1999


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).



Brownlee                     Informational                      [Page 7]

RFC 2723              SRL: A Traffic Flow Language          October 1999


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.












Brownlee                     Informational                      [Page 8]

RFC 2723              SRL: A Traffic Flow Language          October 1999


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:



Brownlee                     Informational                      [Page 9]

RFC 2723              SRL: A Traffic Flow Language          October 1999


             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




Brownlee                     Informational                     [Page 10]

RFC 2723              SRL: A Traffic Flow Language          October 1999


   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 -------- ;
                 |                            |
                 +-------------<--------------+






Brownlee                     Informational                     [Page 11]

RFC 2723              SRL: A Traffic Flow Language          October 1999


   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.





Brownlee                     Informational                     [Page 12]

RFC 2723              SRL: A Traffic Flow Language          October 1999


   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
   #
      define IPv4 = 1;  # Address Family number from [ASG-NBR]
   #
      define ftp = (20, 21);  # Well-Known Port numbers from [ASG-NBR]
      define telnet = 23;
      define www = 80;
   #
      define tcp = 6;  # Protocol numbers from [ASG-NBR]
      define udp = 17;
   #
      if SourcePeerType == IPv4 save;
      else ignore;  # Not an IPv4 packet
   #
      if (SourceTransType == tcp || SourceTransType == udp) save, {
         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 := '?';
            }
         }
      else save SourceTransType = 0;
   #
      save SourcePeerAddress /32;
      save DestPeerAddress   /32;
      count;
   #







Brownlee                     Informational                     [Page 13]

RFC 2723              SRL: A Traffic Flow Language          October 1999


   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.





Brownlee                     Informational                     [Page 14]

RFC 2723              SRL: A Traffic Flow Language          October 1999


   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  Security Considerations

   SRL is a language for creating rulesets (i.e. configuration files)
   for RTFM Traffic Meters - it does not present any security issues in
   itself.

   On the other hand, flow data gathered using such rulesets may well be
   valuable.  It is therefore important to take proper precautions to
   ensure that access to the meter and its data is secure.  Ways to
   achieve this are discussed in detail in the Architecture and Meter
   MIB documents [RTFM-ARC, RTFM-MIB].

6  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 [RTFM-MIB].

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






Brownlee                     Informational                     [Page 15]

RFC 2723              SRL: A Traffic Flow Language          October 1999


7  APPENDICES

7.1  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> ::=  ; |



Brownlee                     Informational                     [Page 16]

RFC 2723              SRL: A Traffic Flow Language          October 1999


                            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> :



Brownlee                     Informational                     [Page 17]

RFC 2723              SRL: A Traffic Flow Language          October 1999


   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

7.2  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.

   IPv6 addresses and masks may also be used, following the conventions
   set out in the IP Version 6 Addressing Architecture RFC [V6-ADR].






Brownlee                     Informational                     [Page 18]

RFC 2723              SRL: A Traffic Flow Language          October 1999


7.3  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 maximum size (in
   bytes) is shown to the left, and a brief description is given for
   each.  The names given here are reserved words in SRL (they are
   <attribute> terminals in the grammar given in Appendix A).

   Note that this table gives only a very brief summary.  The Meter MIB
   [RTFM-MIB] provides the definitive specification of attributes and
   their allowed values.  The MIB variables which represent flow
   attributes have 'flowData' prepended to their names to indicate that
   they belong to the MIB's flowData table.

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

   1  SourceAdjacentType, DestAdjacentType
         Indicates the interface type(s), i.e. an ifType from [ASG-NBR],
         or an Address Family Number (if metering within a tunnel)

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

   1  SourcePeerType, DestPeerType
         Peer protocol types, i.e. Address Family Number from [ASG-NBR],
         such as IPv4, Novell, Ethertalk, ..

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

   1  SourceTransType, DestTransType
         Transport layer type, i.e. Protocol Number from [ASG-NBR]
         such as tcp(6), udp(17), ospf(89), ..

   2  SourceTransAddress, DestTransAddress
         Transport layer addresses (e.g. 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 [RTFM-ARC] 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.




Brownlee                     Informational                     [Page 19]

RFC 2723              SRL: A Traffic Flow Language          October 1999


      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, LastActiveTime
         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.

8  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.

9  References

   [ASG-NBR]  Reynolds, J. and J. Postel, "Assigned Numbers",
              STD 2, RFC 1700, October 1994.

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

   [RTFM-ARC] Brownlee, N., Mills, C. and G. Ruth, "Traffic Flow
              Measurement: Architecture", RFC 2722, October 1999.

   [RTFM-MIB] Brownlee, N., "Traffic Flow Measurement: Meter MIB",
              RFC 2720, October 1999.

   [V6-ADDR]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture," RFC 2373, July 1998.





Brownlee                     Informational                     [Page 20]

RFC 2723              SRL: A Traffic Flow Language          October 1999


10  Author's Address

   Nevil Brownlee
   Information Technology Systems & Services
   The University of Auckland
   Private Bag 92-019
   Auckland, New Zealand

   Phone: +64 9 373 7599 x8941
   EMail: n.brownlee@auckland.ac.nz









































Brownlee                     Informational                     [Page 21]

RFC 2723              SRL: A Traffic Flow Language          October 1999


11  Full Copyright Statement

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















Brownlee                     Informational                     [Page 22]