Loop in AS macro

Ping,

What I usually do (in Perl) is something like this:

my %entries_seen;
foreach my $as_set (@as_sets) {
    # if we've seen this value (recursive as-set), skip
    next if ($entries_seen{$as_set});

    # note that we've seen this as-set
    $entries_seen{$as_set}++;

    # get a list of members of the as-set, and process appropriately
    foreach my $member (members($as_set)) {
        # add member as-sets to the list of as-sets to process
        push(@as_sets, $member) if ($member =~ /^AS-/i);

        # other processing here
          .
          .
          .
    }
}

If you're using some other scripting language, it will be different, but
typically no more difficult.  If you're in C, you may want to use glib or
something like that, otherwise you'll need to use a list or hash you write
yourself.

Shane Kerr <shane at ripe.net>
Database Software Engineer
RIPE NCC
+31 20 535 4427

On Wed, 10 Jan 2001, Lu, Ping wrote:

> Hi, I am new to this list and would like to ask a (maybe stupid) question to
> the dicussion:
> 
> If we want to write a script to expand the AS MACRO, how can we avoid to go
> into a loop if multiple AS-MACROs reference each other ?
> 
> Ping Lu
> Cable & Wireless USA
> Network Tools and Analysis Group
> W: 703-292-2359
> E: plu at cw.net
> 
> > -----Original Message-----
> > From: Cengiz Alaettinoglu [mailto:cengiz at packetdesign.com]
> > Sent: Wednesday, January 10, 2001 12:14 PM
> > To: Shane Kerr
> > Cc: Wilfried Woeber, UniVie/ACOnet; farrache at cc.in2p3.fr;
> > db-wg at ripe.net; routing-wg at ripe.net; Henk.Uijterwaal at ripe.net
> > Subject: RE: Loop in AS macro
> > 
> > 
> > 
> > Shane Kerr (shane at ripe.net) on January 10:
> > > Gilles, Wilfried, and all,
> > > 
> > > This is not a bug, or even an inconsistency.  Consider the following
> > > as-macro objects:
> > > 
> > >   as-macro: AS-X
> > >   members:  AS-Y, AS123
> > > 
> > >   as-macro: AS-Y
> > >   members:  AS-X, AS456, AS789
> > > 
> > > In this case, AS-X and AS-Y both expand to the same aut-num objects:
> > > AS123, AS456, and AS789.  However, they may have different 
> > maintainers,
> > > contacts, descriptions, and so on.  In RPSL, many more 
> > kinds of loops are
> > > possible as well, in as-set, route-set, and filter-set objects.
> > 
> > RPSL defines semantics when loops exist. However, it does not promote
> > them, or prohibit additional restrictions by the registry operators
> > not to have loops.
> > 
> > > 
> > > External software that deals with the set objects needs to do loop
> > > detection in order to prevent infinite loops.  For as-set 
> > objects (which
> > > are as-macro objects in RIPE-181), this is fairly easy:  
> > keep a list or
> > > hash of the AS sets expanded, and don't expand them again.  
> > For route-set
> > > and filter-set objects it is not quite so easy.  If you 
> > need help with
> > > these, you can send me and e-mail and I can explain the 
> > techniques that
> > > I've used for these objects.
> > > 
> > > Shane Kerr <shane at ripe.net>
> > > Database Software Engineer
> > > RIPE NCC
> > > +31 20 535 4427
> > > 
> > > p.s.  This is actually a feature, not an bug.  :)
> > > 
> > > p.p.s.  It has been argued (by me) that RPSL allows objects that are
> > > logically impossible, but the RFC authors don't seem to think so!
> > > 
> > > On Wed, 10 Jan 2001, Wilfried Woeber, UniVie/ACOnet wrote:
> > > 
> > > >   Hi Gilles,
> > > >   
> > > >   I guess we wouldn't be able to check against those 
> > accidents at the time
> > > >   of a DB _update_...
> > > >   
> > > >   But checking the RR internal _data_ consistency could 
> > maybe become part
> > > >   of the RIS (or similar) project?
> > > >   
> > > >   Henk, any comments?
> > > >   
> > > >   An interesting aside: I guess similar problems could occur with
> > > >   RPSL-based RRs?
> > > >   
> > > >   -WW
> > > >  
> > _________________________________:____________________________
> > _________
> > > >   Wilfried Woeber                 : e-mail: Woeber at CC.UniVie.ac.at
> > > >   UniVie Computer Center - ACOnet : Tel: +43 1 4277 - 140 33
> > > >   Universitaetsstrasse 7          : Fax: +43 1 4277 - 9 140
> > > >   A-1010 Vienna, Austria, Europe  : RIPE-DB: WW144, PGP 
> > keyID 0xF0ACB369
> > > >  
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~:~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > ~~~~~~~~~
> > > > 
> > > > To: staff at ip.tele.dk, peering at tli.de, ip-oper at tli.de, 
> > admin-c at tli.de
> > > > CC: farrache at cc.in2p3.fr, db-wg at ripe.net, routing-wg at ripe.net
> > > > Subject: Loop in AS macro
> > > > Date: Wed, 10 Jan 2001 10:28:15 +0100
> > > > From: Gilles Farrache <farrache at cc.in2p3.fr>
> > > > 
> > > > Dear database managers,
> > > > 
> > > > I notice a loop in the followings AS-MACRO, in fact  
> > AS-TELEDANMARKINTERNATIONAL
> > > > is calling AS-TLI which is calling AS-TELEDK which is 
> > calling AS-TELEDANMARKINTERNATIONAL.
> > > > (and all that make that our automatic filter generation 
> > tool fails)
> > > > 
> > > > Could you correct those macro and will the Ripe database 
> > management provide any 
> > > > control on that kind of loop ?
> > > > 
> > > > Gilles 
> > > > 
> > > > as-macro:    AS-TELEDANMARKINTERNATIONAL
> > > > descr:       Tele Danmark customers outside Denmark
> > > > as-list:     AS1902 AS12461
> > > > as-list:     AS8881 AS-KOMTEL
> > > > as-list:     AS13194 AS-BITE
> > > > as-list:     AS6709
> > > > as-list:     AS8650 AS-TLI
> > > > as-list:     AS8542
> > > > as-list:     AS12294 AS-TSUA AS6807 AS8349 AS12788 
> > AS12837 AS12872 AS13249 AS15386 AS15497 AS15929 AS16007
> > > > as-list:     AS12546
> > > > as-list:     AS15389
> > > > tech-c:      AS5071-RIPE
> > > > admin-c:     AS5071-RIPE
> > > > notify:      staff at ip.tele.dk
> > > > notify:      peering at tli.de
> > > > mnt-by:      AS3292-MNT
> > > > changed:     jesper at skriver.dk 20001103
> > > > changed:     toba at tdk.dk 20001117
> > > > changed:     tee at tdk.dk 20001123
> > > > changed:     jesper at skriver.dk 20001228
> > > > changed:     jesper at skriver.dk 20010109
> > > > source:      RIPE
> > > > 
> > > > as-macro:    AS-TLI
> > > > descr:       Talkline GmbH, Internet Division
> > > > descr:       List of ASes according to Talkline Internet (AS8650)
> > > > descr:       and customers
> > > > as-list:     AS5605
> > > > as-list:     AS6783
> > > > as-list:     AS8650
> > > > as-list:     AS8881
> > > > as-list:     AS12461
> > > > as-list:     AS12546
> > > > as-list:     AS-TELEDK
> > > > as-list:     AS-GLOBAL
> > > > tech-c:      TLIP1-RIPE
> > > > admin-c:     TLIP1-RIPE
> > > > notify:      peering at tli.de
> > > > mnt-by:      TALKLINE-MNT
> > > > changed:     thomas at tli.de 19990923
> > > > changed:     thomas at tli.de 19991020
> > > > changed:     thomas at tli.de 19991025
> > > > changed:     thomas at tli.de 20001023
> > > > changed:     thomas at tli.de 20001025
> > > > source:      RIPE
> > > > 
> > > > as-macro:    AS-TELEDK
> > > > descr:       Tele Danmark and Tele Danmark customers
> > > > as-list:     AS-TELEDANMARKDANISH
> > > > as-list:     AS-TELEDANMARKINTERNATIONAL
> > > > as-list:     AS-BELBONEMEMBERS
> > > > as-list:     AS-GLOBAL
> > > > tech-c:      AS5071-RIPE
> > > > admin-c:     AS5071-RIPE
> > > > notify:      staff at ip.tele.dk
> > > > notify:      peering at tli.de
> > > > mnt-by:      AS3292-MNT
> > > > changed:     jesper at skriver.dk 19990922
> > > > changed:     jesper at skriver.dk 19991019
> > > > changed:     jesper at skriver.dk 19991025
> > > > changed:     jesper at skriver.dk 19991210
> > > > changed:     toba at tdk.dk 20000903
> > > > source:      RIPE
> > > > 
> > --------------------------------------------------------------
> > ------------------
> > > > 
> > > 
> > > 
> > 
> > 
> > Cengiz
> > 
> > -- 
> > Cengiz Alaettinoglu           Packet Design Inc.
> > 
> > 
>