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rfc:rfc2650

Network Working Group D. Meyer Request for Comments: 2650 Cisco Systems Category: Informational J. Schmitz

                                                       America On-Line
                                                             C. Orange
                                                              RIPE NCC
                                                              M. Prior
                                                               Connect
                                                       C. Alaettinoglu
                                                               USC/ISI
                                                           August 1999
                       Using RPSL in Practice

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 is a tutorial on using the Routing Policy Specification
 Language (RPSL) to describe routing policies in the Internet Routing
 Registry (IRR). We explain how to specify various routing policies
 and configurations using RPSL, how to register these policies in the
 IRR, and how to analyze them using the routing policy analysis tools,
 for example to generate vendor specific router configurations.

1 Introduction

 This document is a tutorial on RPSL and is targeted towards an
 Internet/Network Service Provider (ISP/NSP) engineer who understands
 Internet routing, but is new to RPSL and to the IRR. Readers are
 referred to the RPSL reference document (RFC 2622) [1] for
 completeness.  It is also good to have that document at hand while
 working through this tutorial.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119.

Meyer, et al. Informational [Page 1] RFC 2650 Using RPSL in Practice August 1999

 The IRR is a repository of routing policies.  Currently, the IRR
 repository is a set of five repositories maintained at the following
 sites:  the CA*Net registry in Canada, the ANS, CW and RADB
 registries in the United States of America, and the RIPE registry in
 Europe.  The five repositories are run independently.  However, each
 site exchanges its data with the others regularly (at least once a
 day and as often as every ten minutes).  CW, CA*Net and ANS are
 private registries which contain the routing policies of the networks
 and the customer networks of CW, CA*Net, and ANS respectively.  RADB
 and RIPE are both public registries, and any ISP can publish their
 policies in these registries.
 The registries all maintain up-to-date copies of one another's data.
 At any of the sites, the five registries can be inspected as a set.
 One should refrain from registering his/her data in more than one of
 the registries, as this practice leads almost invariably to
 inconsistencies in the data.  The user trying to interpret the data
 is left in a confusing (at best) situation.  CW, ANS and CA*Net
 customers are generally required to register their policies in their
 provider's registry.  Others may register policies either at the RIPE
 or RADB registry, as preferred.
 RPSL is based on RIPE-181 [2, 3], a language used to register routing
 policies and configurations in the IRR. Operational use of RIPE-181
 has shown that it is sometimes difficult (or impossible) to express a
 routing policy which is used in practice.  RPSL has been developed to
 address these shortcomings and to provide a language which can be
 further extended as the need arises.  RPSL obsoletes RIPE-181.
 RPSL constructs are expressed in one or more database "objects" which
 are registered in one of the registries described above.  Each
 database object contains some routing policy information and some
 necessary administrative data.  For example, an address prefix routed
 in the inter-domain mesh is specified in a route object, and the
 peering policies of an AS are specified in an aut-num object.  The
 database objects are related to each other by reference.  For
 example, a route object must refer to the aut-num object for the AS
 in which it is originated.  Implicitly, these relationships define
 sets of objects, which can be used to specify policies effecting all
 members.  For example, we can specify a policy for all routes of an
 ISP, by referring to the AS number in which the routes are registered
 to be originated.
 When objects are registered in the IRR, they become available for
 others to query using a whois service.  Figure 1 illustrates the use
 of the whois command to obtain the route object for 128.223.0.0/16.
 The output of the whois command is the ASCII representation of the
 route object.  The syntax and semantics of the route object are

Meyer, et al. Informational [Page 2] RFC 2650 Using RPSL in Practice August 1999

 described in Appendix A.3.  Registered policies can also be compared
 with others for consistency and they can be used to diagnose
 operational routing problems in the Internet.
    % whois -h whois.ra.net 128.223.0.0/16
      route:       128.223.0.0/16
      descr:       UONet
      descr:       University of Oregon
      descr:       Computing Center
      descr:       Eugene, OR 97403-1212
      descr:       USA
      origin:      AS3582
      mnt-by:      MAINT-AS3582
      changed:     meyer@ns.uoregon.edu 19960222
      source:      RADB
    Figure 1:  whois command and a route object.
 The RAToolSet [6] is a suite of tools which can be used to analyze
 the routing registry data.  It includes tools to configure routers
 (RtConfig), tools to analyze paths on the Internet (prpath and
 prtraceroute), and tools to compare, validate and register RPSL
 objects (roe, aoe and prcheck).
 In the following section, we will describe how common routing
 policies can be expressed in RPSL. The objects themselves are
 described in Appendix A.  Authoritative information on the IRR
 objects, however, should be sought in RFC-2622, and authoritative
 information on general database objects (person, role, and
 maintainers) and on querying and updating the registry databases,
 should be sought in RIPE-157 [4].  Section 3.2 describes the use of
 RtConfig to generate vendor specific router configurations.

2 Specifying Policy in RPSL

 The key purpose of RPSL is to allow you to specify your routing
 configuration in the public Internet Routing Registry (IRR), so that
 you and others can check your policies and announcements for
 consistency.  Moreover, in the process of setting policies and
 configuring routers, you take the policies and configurations of
 others into account.
 In this section, we begin by showing how some simple peering policies
 can be expressed in RPSL. We will build on that to introduce various
 database objects that will be needed in order to register policies in
 the IRR, and to show how more complex policies can be expressed.

Meyer, et al. Informational [Page 3] RFC 2650 Using RPSL in Practice August 1999

2.1 Common Peering Policies

 The peering policies of an AS are registered in an aut-num object
 which looks something like that in Figure 2.  We will focus on the
 semantics of the import and export attributes in which peering
 policies are expressed.  We will also describe some of the other key
 attributes in the aut-num object, but the reader should refer to
 RFC-2622 or to RIPE-157 for the definitive descriptions.
    aut-num:     AS2
    as-name:     CAT-NET
    descr:       Catatonic State University
    import:      from AS1 accept ANY
    import:      from AS3 accept <^AS3+$>
    export:      to AS3 announce ANY
    export:      to AS1 announce AS2 AS3
    admin-c:     AO36-RIPE
    tech-c:      CO19-RIPE
    mnt-by:      OPS4-RIPE
    changed:     orange@ripe.net
    source:      RIPE
    Figure 2:  Autonomous System Object
 Now consider Figure 3 (AS4 and AS5 in the figure will be discussed
 later).  The peering policies expressed in the AS2 aut-num object in
 Figure 2 are typical for a small service provider providing
 connectivity for a customer AS3 and using AS1 for transit.  That is,
 AS2 only accepts announcements from AS3 which:
 o  are originated in AS3; and
 o  have paths composed of only AS3's (^ in <^AS3+$> means that AS3 is
    the first member of the path, + means that AS3 occurs one or more
    times in the path, and $ means that no other AS can be present in
    the path after AS3) (1).
 To AS1, AS2 announces only those routes which originate in their AS
 or in their customer's AS.
    AS1--------AS2--------AS3
                |          |
                |          |
               AS4--------AS5
    Figure 3:  Some Neighboring ASes.

Meyer, et al. Informational [Page 4] RFC 2650 Using RPSL in Practice August 1999

 In the example above, "accept ANY" in the import attribute indicates
 that AS2 will accept any announcements that AS1 sends, and "announce
 ANY" in the export attribute indicates that any route that AS2 has in
 its routing table will be passed on to AS3.  Assuming that AS1
 announces "ANY" to AS2, AS2 is taking full routing from AS1.
 Note that with this peering arrangement, if AS1 adds or deletes route
 objects, there is no need to update any of the aut-num objects to
 continue the full routing policy.  Added (or deleted) route objects
 will implicitly update AS1's and AS2's policies.
 While the peering policy specified in Figure 2 for AS2 is common, in
 practice many peering agreements are more complex.  Before we
 consider more examples, however, let's first consider the aut-num
 object itself.  Note that it is just a set of attribute labels and
 values which can be submitted to one of the registry databases.  This
 particular object is specified as being in (or headed for) the RIPE
 registry (see the last line in Figure 2).  The source should be
 specified as one of ANS, CANET, CW, RADB, or RIPE depending on the
 registry in which the object is maintained.  The source attribute
 must be specified in every database object.
 It is also worth noting that this object is "maintained by" OPS4-RIPE
 (the value of the mnt-by attribute), which references a "mntner"
 object.  Because the aut-num object may be used for router
 configuration and other operational purposes, the readers need to be
 able to count on the validity of its contents.  It is therefore
 required that a mntner be specified in the aut-num and in most other
 database objects, which means you must create a mntner object before
 you can register your peering policies.  For brief information on the
 "mntner" object and object writeability, see Appendix A of this
 document.  For more extensive information on how to set up and use a
 mntner to protect your database objects, see Section 2.3 of RIPE-157.

2.2 ISP Customer - Transit Provider Policies

 It is not uncommon for an ISP to acquire connectivity from a transit
 provider which announces all routes to it, which it in turn passes on
 to its customers to allow them to access hosts on the global
 Internet.  Meanwhile, the ISP will generally announce the routes of
 its customers networks to the transit ISP, making them accessible on
 the global Internet.  This is the service that is specified in Figure
 2 for AS3.
 Consider again Figure 3.  Suppose now that AS2 wants to provide the
 same service to AS4.  Clearly, it would be easy to modify the import
 and export lines in the aut-num object for AS2 (Figure 2) to those
 shown in Figure 4.

Meyer, et al. Informational [Page 5] RFC 2650 Using RPSL in Practice August 1999

    import:      from AS1 accept ANY
    import:      from AS3 accept <^AS3+$>
    import:      from AS4 accept <^AS4+$>
    export:      to AS3 announce ANY
    export:      to AS4 announce ANY
    export:      to AS1 announce AS2 AS3 AS4
    Figure 4:  Policy for AS3 and AS4 in the AS2 as-num object
 These changes are trivial to make of course, but clearly as the
 number of AS2 customers grows, it becomes more difficult to keep
 track of, and to prevent errors.  Note also that if AS1 is selective
 about only accepting routes from the customers of AS2 from AS2, the
 aut-num object for AS1 would have to be adjusted to accommodate AS2's
 new customer.
 By using the RPSL "as-set" object, we can simplify this
 significantly.  In Figure 5, we describe the customers of AS2.
 Having this set to work with, we can now rewrite the policies in
 Figure 2 as shown in Figure 6.
    as-set:      AS2:AS-CUSTOMERS
    members:     AS3 AS4
    changed:     orange@ripe.net
    source:      RIPE
    Figure 5:  The as-set object
    import:      from AS1 accept ANY
    import:      from AS2:AS-CUSTOMERS accept <^AS2:AS-CUSTOMERS+$>
    export:      to AS2:AS-CUSTOMERS announce ANY
    export:      to AS1 announce AS2 AS2:AS-CUSTOMERS
    Figure 6:  Policy in the AS2 aut-num object for all AS2 customers
 Note that if the aut-num object for AS1 contains the line:
    import:      from AS2 accept <^AS2+ AS2:AS-CUSTOMERS*$>
 then no changes will need to be made to the aut-num objects for AS1
 or AS2 as the AS2 customer base grows.  The AS numbers for new
 customers can simply be added to the as-set AS2:AS-CUSTOMERS, and
 everything will work as for the existing customers.  Clearly in terms
 of readability, scalability and maintainability, this is a far better
 mechanism when compared to adding policy for the customer AS's to the
 aut-num objects directly.  The policy in this particular example
 states that AS1 will accept route announcements from AS2 in which the
 first element of the path is AS2, followed by more occurrences of

Meyer, et al. Informational [Page 6] RFC 2650 Using RPSL in Practice August 1999

 AS2, and then 0 or more occurrences of any AS2 customer (e.g.  any
 member of the as-set AS2:AS-CUSTOMERS).
 Alternatively, one may wish to limit the routes one accepts from a
 peer, especially if the peer is a customer.  This is recommended for
 several reasons, such as preventing the improper use of unassigned
 address space, and of course malicious use of another organization's
 address space.
 Such filtering can be expressed in various ways in RPSL. Suppose the
 address space 7.7.0.0/16 has been allocated to the ISP managing AS3
 for assignment to its customers.  AS3 may want to announce part or
 all of this block on the global Internet.  Suppose AS2 wants to be
 certain that it only accepts announcements from AS3 for address space
 that has been properly allocated to AS3.  AS2 might then modify the
 AS3 import line in Figure 2 to read:
    import:      from AS3 accept { 7.7.0.0/16^16-19 }
 which states that route announcements for this address block will be
 accepted from AS3 if they are of length upto /19.  This of course
 will have to be modified if and when AS3 gets more address space.
 Moreover, it is again clear that for an ISP with a growing or
 changing customer base, this mechanism will not scale well.
    route-set:   AS2:RS-ROUTES:AS3
    members:     7.7.0.0/16^16-19
    changed:     orange@ripe.net
    source:      RIPE
    Figure 7:  The route-set object
 Luckily RPSL supports the notion of a "route-set" which, as shown in
 Figure 7, can be used to specify the set of routes that will be
 accepted from a given customer.  Given this set (and a similar one
 for AS4), the manager of AS2 can now filter on the address space that
 will be accepted from their customers by modifying the import lines
 in the AS2 aut-num object as shown in Figure 8.
    import:      from AS1 accept ANY
    import:      from AS3 accept AS2:RS-ROUTES:AS3
    import:      from AS4 accept AS2:RS-ROUTES:AS4
    export:      to AS2:AS-CUSTOMERS announce ANY
    export:      to AS1 announce AS2 AS2:AS-CUSTOMERS
    Figure 8:  Policy in the AS2 aut-num object for address based
               filtering on AS2 customers

Meyer, et al. Informational [Page 7] RFC 2650 Using RPSL in Practice August 1999

 Note that this is now only slightly more complex than the example in
 Figure 6.  Furthermore, nothing need be changed in the AS2 aut-num
 object due to address space changes for a customer, and this
 filtering can be supported without any changes to the AS1 aut-num
 object.  The additional complexity is due to the two route set names
 being different, otherwise we could have combined the two import
 statements into one.  Please note that the set names are constructed
 hierarchically.  The first AS number denotes whose sets these are,
 and the last AS number parameterize these sets for each peer.  RPSL
 allows the peer's AS number to be replaced by the keyword PeerAS.
 Hence,
    import:      from AS3 accept AS2:RS-ROUTES:PeerAS
    import:      from AS4 accept AS2:RS-ROUTES:PeerAS
 has the same meaning as the corresponding import statements in Figure
 6.  This lets us combine the two import statements into one as shown
 in Figure 9.
    import:      from AS1 accept ANY
    import:      from AS2:AS-CUSTOMERS accept AS2:RS-ROUTES:PeerAS
    export:      to AS2:AS-CUSTOMERS announce ANY
    export:      to AS1 announce AS2 AS2:AS-CUSTOMERS
    Figure 9:  Policy in the AS2 aut-num object using PeerAS

2.3 Including Interfaces in Peering Definitions

 In the above examples peerings were only given among ASes.  However,
 the peerings may be described in much more detail by RPSL, where
 peerings can be specified between physical routers using IP addresses
 in the import and export attributes.  Figure 10 shows a simple
 example in which AS1 and AS2 are connected to an exchange point IX.
 While AS1 has only one connection to the exchange point via a router
 interface with IP address 7.7.7.1, AS2 has two different connections
 with IP address 7.7.7.2 and 7.7.7.3.  The first AS may then define
 its routing policy in more detail by specifying its boundary router.
    +--------------------+                +--------------------+
    |            7.7.7.1 |-----+    +-----| 7.7.7.2            |
    |                    |     |    |     |                    |
    | AS1                |    ========    |                AS2 |
    |                    |    IX    |     |                    |
    |                    |          +-----| 7.7.7.3            |
    +--------------------+                +--------------------+
    Figure 10:  Including interfaces in peerings definitions

Meyer, et al. Informational [Page 8] RFC 2650 Using RPSL in Practice August 1999

    aut-num:   AS1
    import:    from AS2 at 7.7.7.1 accept <^AS2+$>
 Because AS1 has only one connection to the exchange point in this
 example, this specification does not differ from that in which no
 boundary router is specified.  However, AS1 might want to choose to
 accept only those announcements from AS2 which come from the router
 with IP address 7.7.7.2 and disregard those announcements from router
 7.7.7.3.  AS1 can specify this routing policy as follows:
    aut-num:   AS1
    import:    from AS2 7.7.7.2 at 7.7.7.1 accept <^AS2+$>
 By selecting certain pairs of routers in a peering specification,
 others can be denied.  If no routers are included in a policy clause
 then it is assumed that the policy applies to all peerings among the
 ASes involved.

2.4 Describing Simple Backup Connections

 The specification of peerings among ASes is not limited to one router
 for each AS. In figure 10 one of the two connections of AS2 to the
 exchange point IX might be used as backup in case the other
 connection fails.  Let us assume that AS1 wants to use the connection
 to router 7.7.7.2 of AS2 during regular operations, and router
 7.7.7.3 as backup.  In a router configuration this may be done by
 setting a local preference.  The equivalent in RPSL is a
 corresponding action definition in the peering description.  The
 action definitions are inserted directly before the accept keyword.
    aut-num:   AS1
    import:    from AS2 7.7.7.2 at 7.7.7.1 action pref=10;
               from AS2 7.7.7.3 at 7.7.7.1 action pref=20;
               accept <^AS2+$>
 pref is opposite to local-pref in that the smaller values are
 preferred over larger values.  Actions may also be defined without
 specifying IP addresses of routers.  If no routers are included in
 the policy clause then it is assumed that the actions are carried out
 for all peerings among the ASes involved.
 In the previous example AS1 controls where it sends its traffic and
 which connection is used as backup.  However, AS2 may also define a
 backup connection in an export clause:

Meyer, et al. Informational [Page 9] RFC 2650 Using RPSL in Practice August 1999

    aut-num:   AS2
    export:    to AS1 7.7.7.1 at 7.7.7.2 action med=10;
               to AS1 7.7.7.1 at 7.7.7.3 action med=20;
               announce <^AS2+$>
 The definition given here for AS2 is the symmetric counterpart to the
 routing policy of AS1.  The selection of routing information is done
 by setting the multi exit discriminator metric med.  Actually, med
 metrics will not be used in practice like this; they are more
 suitable for load balancing including backups.  For more details on
 med metrics refer to the BGP-4 RFC [7].  To use the med to achieve
 load balancing, one often sets it to the "IGP metric".  This is
 specified in RPSL as:
    aut-num:   AS2
    export:    to AS1 action med=igp_cost; announce <^AS2+$>
 Hence, both routers will set the med to the IGP metric at that
 router, causing some routes to be preferred at one of the routers and
 other routes at the other router.

2.5 Multi-Home Routing Policies using the community Attribute

 RFC 1998 [9] describes the use of the BGP community attribute to
 provide support for load balancing and backup connections of multi-
 homed autonomous systems.  In this section, we use stepwise
 refinement of an example to illustrate how those policies might be
 specified using RPSL.
 The basic premise of RFC 1998 is to use the BGP community attribute
 to allow a customer to configure the BGP "LOCAL_PREF" on a provider's
 routers.  This will allow the customer to influence the provider's
 route selection, normally by lowering the BGP "LOCAL_PREF" to
 indicate backup arrangements.
 In this example, we illustrate how AS1 (the provider) might specify
 their policy so that a customer (AS4) connected to two of AS1's
 direct customers (AS2 and AS3) might signal to AS1 which connection
 is to be preferred.
 AS1's base policy is to only accept routes from customers that are
 originated by the customer, or by the customer's customers.  This
 leads to a policy such as:

Meyer, et al. Informational [Page 10] RFC 2650 Using RPSL in Practice August 1999

    aut-num:     AS1
    import:      from AS2
                 accept (AS2 OR AS4) AND <^AS2+ AS4*$>
    import:      from AS3
                 accept (AS3 OR AS4) AND <^AS3+ AS4*$>
    import:      from AS5
                 accept AS5 AND <^AS5+$>
 Note that AS4 is a customer of AS2 and AS3, and AS5 does not have its
 own customers.
 Now suppose we want to add some policy to describe that if a customer
 tags a route with community 1:1 then AS1 will act on this to reduce
 the BGP "LOCAL_PREF" by 10.
 aut-num: AS1
 import:  from AS2
          action pref=10;
          accept (AS2 OR AS4) AND <^AS2+ AS4*$>
                  AND community.contains(1:1)
 import:  from AS2
          action pref=0;
          accept (AS2 OR AS4) AND <^AS2+ AS4*$>
 import:  from AS3
          action pref=10;
          accept (AS3 OR AS4) AND <^AS3+ AS4*$>
                  AND community.contains(1:1)
 import:  from AS3
          action pref=0;
          accept (AS3 OR AS4) AND <^AS3+ AS4*$>
 import:  from AS5
          action pref=10;
          accept AS5 AND <^AS5+$> AND community.contains(1:1)
 import:  from AS5
          action pref=0;
          accept AS5 AND <^AS5+$>
 We can see here that basically we are adding identical statements for
 each peering to the policy.  This is the ideal candidate for RPSL's
 refine statement.  This will make the policy more concise and avoid
 some of the potential for errors as more peering statements are added
 in the future:

Meyer, et al. Informational [Page 11] RFC 2650 Using RPSL in Practice August 1999

    aut-num:     AS1
    import: {
                 from AS-ANY
                      action pref=10;
                      accept community.contains(1:1);
                 from AS-ANY
                      action pref=0;
                      accept ANY;
             } refine {
                 from AS2 accept (AS2 OR AS4) AND <^AS2+ AS4*$>;
                 from AS3 accept (AS3 OR AS4) AND <^AS3+ AS4*$>;
                 from AS5 accept AS5 AND <^AS5+$>;
             }
 Now, we can clearly see that any route that has been accepted from a
 customer that contains the community 1:1 will have it's local
 preference value reduced by 10.
 The refinement has cleaned up some of the policy but we still have a
 large number of individual policies representing the same basic
 provider policy "from the customer, accept customer routes".  These
 can be simplified by using AS sets.
 First, we will collect together all of AS1's customers into a single
 AS set, AS1:AS-CUSTOMERS. We use a hierarchical set name that start
 with AS1 to avoid possible set name clashes in IRR with other ASes:
  as-set:      AS1:AS-CUSTOMERS
  members:     AS2, AS3, AS5
 We also define one set for each customer which lists the AS numbers
 of any of their customers.
  as-set:      AS1:AS-CUSTOMERS:AS2
  members:     AS4
  as-set:      AS1:AS-CUSTOMERS:AS3
  members:     AS4
  as-set:      AS1:AS-CUSTOMERS:AS5
  members:     # AS5 has no customers yet, so keep blank for now
 We can now use the keyword PeerAS with these AS sets to simplify the
 policy further:

Meyer, et al. Informational [Page 12] RFC 2650 Using RPSL in Practice August 1999

    aut-num:     AS1
    import: {
                 from AS-ANY
                      action pref=10;
                      accept community.contains(1:1);
                 from AS-ANY
                      action pref=0;
                      accept ANY;
            } refine {
                 from AS1:AS-CUSTOMERS
                      accept (PeerAS OR AS1:AS-CUSTOMER:PeerAS)
                             AND <^PeerAS+ AS1:AS-CUSTOMER:PeerAS*$>
            }
 The use of PeerAS with AS1:AS-CUSTOMERS is basically equivalent to
 looping over the members of AS1:AS-CUSTOMERS, expanding the policy by
 replacing PeerAS with a member from the set AS1:AS-CUSTOMERS.
 To illustrate how this policy might be utilised by AS4, we present
 the following policy fragment:
    aut-num: AS4
    export: to AS2
            action community.append(1:1);
            announce AS1
    export: to AS3
            announce AS1
 Here, AS4 is signalling AS1 to prefer the routes from AS3.

3 Tools

 In this section, we briefly introduce a number of tools which can be
 used to inspect data in the database, to determine optimal routing
 policies, and enter new data.

3.1 The aut-num Object Editor

 All the examples shown in the previous sections may well be edited by
 hand.  They may be extracted one by one from the IRR using the whois
 program, edited, and then handed back to the registry robots.
 However, again the RAToolSet [6] provides a very nice tool which
 makes working with aut-num objects much easier:  the aut-num object
 editor aoe.
 The aut-num object editor has a graphical user interface to view and
 manipulate aut-num objects registered at any IRR. New aut-num objects
 may be generated using templates and submitted to the registries.

Meyer, et al. Informational [Page 13] RFC 2650 Using RPSL in Practice August 1999

 Moreover, the routing policy from the databases may be compared to
 real life peerings.  Therefore, aoe is highly recommended as an
 interface to the IRR for aut-num objects.  Further information on aoe
 is available together with the RAToolSet [6].

3.2 Router Configuration Using RtConfig

 RtConfig is a tool developed by the Routing Arbiter project [8] to
 generate vendor specific router configurations from the policy data
 held in the various IRRs.  RtConfig currently supports Cisco, gated
 and RSd configuration formats.  It has been publicly available since
 late 1994, and is currently being used by many sites for router
 configuration.  The next section describes a methodology for
 generating vendor specific router configurations using RtConfig (2).

3.3 Using RtConfig

 The general paradigm for using RtConfig involves registering policy
 in an IRR, building a RtConfig source file, then running running
 RtConfig against the source file and the IRR database to create
 vendor specific router configuration for the specified policy.  The
 source file will contain vendor specific commands as well as RtConfig
 commands.  To make a source file, pick up one of your router
 configuration files and replace the vendor specific policy
 configuration commands with the RtConfig commands.
 Commands beginning with @RtConfig instruct RtConfig to perform
 special operations.  An example source file is shown in Figure 11.
 In this example, commands such as "@RtConfig import AS3582
 198.32.162.1 AS3701 198.32.162.2" instruct RtConfig to generate
 vendor specific import policies where the router 198.32.162.1 in
 AS3582 is importing routes from router 198.32.162.2 in AS3701.  The
 other @RtConfig commands instruct the RtConfig to use certain names
 and numbers in the output that it generates (please refer to RtConfig
 manual [8] for additional information).
 Once a source file is created, the file is processed by RtConfig (the
 default IRR is the RADB, and the default vendor is Cisco; however,
 command line options can be used to override these values).  The
 result of running RtConfig on the source file in Figure 11 is shown
 in Figure 19 in Appendix B.

Meyer, et al. Informational [Page 14] RFC 2650 Using RPSL in Practice August 1999

    router    bgp 3582
    network   128.223.0.0
    !
    !       Start with access-list 100
    !
    @RtConfig set cisco_access_list_no = 100
    !
    !       NERO
    neighbor 198.32.162.2 remote-as 3701
    @RtConfig set cisco_map_name = "AS3701-EXPORT"
    @RtConfig export AS3582 198.32.162.1 AS3701 198.32.162.2
    @RtConfig set cisco_map_name = "AS3701-IMPORT"
    @RtConfig import AS3582 198.32.162.1 AS3701 198.32.162.2
    !
    !       WNA/VERIO
    neighbor 198.32.162.6 remote-as 2914
    @RtConfig set cisco_map_name = "AS2914-EXPORT"
    @RtConfig export AS3582 198.32.162.1 AS2914 198.32.162.6
    @RtConfig set cisco_map_name = "AS2914-IMPORT"
    @RtConfig import AS3582 198.32.162.1 AS2914 198.32.162.6
    Figure 11:  RtConfig Template File

Meyer, et al. Informational [Page 15] RFC 2650 Using RPSL in Practice August 1999

A RPSL Database Objects

    In this appendix, we introduce the RPSL objects required to implement many
    typical Internet routing policies.  RFC-2622 and RIPE-157 provide the
    authoritative description for these objects and for the RPSL syntax, but
    this appendix will often be sufficient in practice.
 The frequently needed objects are:
    o  maintainer objects (mntner)
    o  autonomous system number objects (aut-num)
    o  route objects (route)
    o  set objects (as-set, route-set)
 and they are described in the following sections.  To make your
 routing policies and configuration public, these objects should be
 registered in exactly one of the IRR registries.
 In general, you can register your information by sending the
 appropriate objects to an email address for the registry you use.
 The email should consist of the objects you want to have registered
 or modified, separated by empty lines, and preceded by some kind of
 authentication details (see below).  The registry robot processes
 your mail and enters new objects into the database, deletes old ones
 (upon request), or makes the requested modifications.
 You will receive a response indicating the status of your submission.
 As the emails are handled automatically, the response is generally
 very fast.  However, it should be remembered that a significant
 number of updates are also sometimes submitted to the database (by
 other robots), so the response time cannot be guaranteed.  The email
 addresses for submitting objects to the existing registries are
 listed in Figure 12.
             ANS    auto-dbm@ans.net
             CANET  auto-dbm@canet.net
             CW     auto-rr@cw.net
             RADB   auto-dbm@ra.net
             RIPE   auto-dbm@ripe.net
    Figure 12:  Email addresses to register policy objects in IRR.

Meyer, et al. Informational [Page 16] RFC 2650 Using RPSL in Practice August 1999

 Because it is required that a maintainer be specified in many of the
 database objects, a mntner is usually the first to be created.  To
 have it properly authenticated, a mntner object is added manually by
 registry staff.  Thereafter, all database submissions, deletions and
 modifications should be done through the registry robot.
 Each of the registries can provide additional information and support
 for users.  For the public registries this support is available from
 the email addresses listed in Figure 13.
             RADB  db-admin@ra.net
             RIPE  ripe-dbm@ripe.net
          Figure 13:  Support email addresses.
 If you are using one of the private registries, your service provider
 should be able to address your questions.

A.1 The Maintainer Object

 The maintainer object is used to introduce some kind of authorization
 for registrations.  It lists various contact persons and describes
 security mechanisms that will be applied when updating objects in the
 IRR.  Registering a mntner object is the first step in creating
 policies for an AS. An example is shown in Figure 14.  The maintainer
 is called MAINT-AS3701.  The contact person here is the same for
 administrative (admin-c) and technical (tech-c) issues and is
 referenced by the NIC-handle DMM65.  NIC-handles are unique
 identifiers for persons in registries.  Refer to registry
 documentation for further details on person objects and usage of
 NIC-handles.
 The example shows two authentication mechanisms:  CRYPT-PW and MAIL-
 FROM.  CRYPT-PW takes as its argument a password that is encrypted
 with Unix crypt (3) routine.  When sending updates, the maintainer
 adds the field password:  <cleartext password> to the beginning of
 any requests that are to be authenticated.  MAIL-FROM takes an
 argument that is a regular expression which covers a set of mail
 addresses.  Only users with any of these mail addresses are
 authorized to work with objects secured by the corresponding
 maintainer (3).
 The security mechanisms of the mntner object will only be applied on
 those objects referencing a specific mntner object.  The reference is
 done by adding the attribute mnt-by to an object using the name of
 the mntner object as its value.  In Figure 14, the maintainer MAINT-
 AS3701 is maintained by itself.

Meyer, et al. Informational [Page 17] RFC 2650 Using RPSL in Practice August 1999

    mntner:      MAINT-AS3701
    descr:       Network for Research and Engineering in Oregon
    remark:      Internal Backbone
    admin-c:     DMM65
    tech-c:      DMM65
    upd-to:      noc@nero.net
    auth:        CRYPT-PW  949WK1mirBy6c
    auth:        MAIL-FROM .*@nero.net
    notify:      noc@nero.net
    mnt-by:      MAINT-AS3701
    changed:     meyer@antc.uoregon.edu 970318
    source:      RADB
    Figure 14:  Maintainer Object

A.2 The Autonomous System Object

 The autonomous system object describes the import and export policies
 of an AS. Each organization registers an autonomous system object
 (aut-num) in the IRR for its AS. Figure 15 shows the aut-num for
 AS3582 (UONET).
 The autonomous system object lists contacts (admin-c, tech-c) and is
 maintained by (mnt-by) MAINT-AS3701 which is the maintainer displayed
 in Figure 14.
 The most important attributes of the aut-num object are import and
 export.  The import clause of an aut-num specifies import policies,
 while the export clause specifies export policies.  The corresponding
 clauses allow a very detailed description of the routing policy of
 the AS specified.  The details are given in section 2.
 With these clauses, an aut-num object shows its relationship to other
 autonomous systems by describing its peerings.  In addition, it also
 defines a routing entity comprising a group of IP networks which are
 handled according to the rules defined in the aut-num object.
 Therefore, it is closely linked to route objects.
 In this example, AS3582 imports all routes from AS3701 by using the
 keyword ANY. AS3582 imports only internal routes from AS4222, AS5650,
 and AS1798.  The import policy for for AS2914 is slightly more
 complex.  Since AS2914 provides transit to various other ASes, AS3582
 accepts routes with ASPATHs that begin with AS2194 followed by
 members of AS-WNA, which is an as set (see section A.4.1 below)
 describing those customers that transit AS2914.

Meyer, et al. Informational [Page 18] RFC 2650 Using RPSL in Practice August 1999

 Since AS3582 is a multi-homed stub AS (i.e., it does not provide
 transit), its export policy consists simply of "announce AS3582"
 clauses; that is, announce internal routes of AS3582.  These routes
 are those in route objects where the origin attribute is AS3582.
    aut-num:     AS3582
    as-name:     UONET
    descr:       University of Oregon, Eugene OR
    import:      from AS3701 accept ANY
    import:      from AS4222 accept <^AS4222+$>
    import:      from AS5650 accept <^AS5650+$>
    import:      from AS2914 accept <^AS2914+ (AS-WNA)*$>
    import:      from AS1798 accept <^AS1798+$>
    export:      to AS3701 announce AS3582
    export:      to AS4222 announce AS3582
    export:      to AS5650 announce AS3582
    export:      to AS2914 announce AS3582
    export:      to AS1798 announce AS3582
    admin-c:     DMM65
    tech-c:      DMM65
    notify:      nethelp@ns.uoregon.edu
    mnt-by:      MAINT-AS3582
    changed:     meyer@antc.uoregon.edu 970316
    source:      RADB
    Figure 15:  Autonomous System Object
 The aut-num object forms the basis of a scalable and maintainable
 router
    route:       128.223.0.0/16
    origin:      AS3582
    descr:       UONet
    descr:       University of Oregon
    descr:       Computing Center
    descr:       Eugene, OR 97403-1212
    descr:       USA
    mnt-by:      MAINT-AS3582
    changed:     meyer@ns.uoregon.edu 960222
    source:      RADB
    Figure 16:  Example of a route object
 configuration system.  For example, if AS3582 originates a new route,
 it need only create a route object for that route with origin AS3582.
 AS3582 can now build configuration using this route object without
 changing its aut-num object.

Meyer, et al. Informational [Page 19] RFC 2650 Using RPSL in Practice August 1999

 Similarly, if for example, AS3701 originates a new route, it need
 only create a route object for that route with origin AS3701.  Both
 AS3701 and AS3582 can now build configuration using this route object
 without modifying its aut-num object.

A.3 The Route Object

 In contrast to aut-num objects which describe propagation of routing
 information for an autonomous system as a whole, route objects define
 single routes from an AS. An example is given in Figure 16.
 This route object is maintained by MAINT-AS3582 and references AS3582
 by the origin attribute.  By this reference it is grouped together
 with other routes of the same origin AS, becoming member of the
 routing entity denoted by AS3582.  The routing policies can then be
 defined in the aut-num objects for this group of routes.
 Consequently, the route objects give the routes from this AS which
 are distributed to peer ASes according to the rules of the routing
 policy.  Therefore, for any route in the routing tables of the
 backbone routers a route object must exist in one of the registries
 in IRR. route objects must be registered in the IRR only for the
 routes seen outside your AS. Normally, this set of external routes is
 different from the routes internally visible within your AS. One of
 the major reasons is that external peers need no information at all
 about your internal routing specifics.  Therefore, external routes
 are in general aggregated combinations of internal routes, having
 shorter IP prefixes where applicable according to the CIDR rules.
 Please see the CIDR FAQ [5] for a tutorial introduction to CIDR. It
 is strongly recommended that you aggregate your routes as much as
 possible, thereby minimizing the number of routes you inject into the
 global routing table and at the same time reducing the corresponding
 number of route objects in the IRR.
 While you may easily query single route objects using the whois
 program, and submit objects via mail to the registry robots, this
 becomes kind of awkward for larger sets.  The RAToolSet [6] offers
 several tools to make handling of route objects easier.  If you want
 to read policy data from the IRR and process it by other programs,
 you might be interested in using peval which is a low level policy
 evaluation tool.  As an example, the command
    peval -h whois.ra.net AS3582
 will give you all route objects from AS3582 registered with RADB.

Meyer, et al. Informational [Page 20] RFC 2650 Using RPSL in Practice August 1999

 A much more sophisticated tool from the RAToolSet to handle route
 objects interactively is the route object editor roe.  It has a
 graphical user interface to view and manipulate route objects
 registered at any IRR. New route objects may be generated from
 templates and submitted to the registries.  Moreover, the route
 objects from the databases may be compared to real life routes.
 Therefore, roe is highly recommended as an interface to the IRR for
 route objects.  Further information on peval and roe is available
 together with the RAToolSet [6].

A.4 Set Objects

 With routing policies it is often necessary to reference groups of
 autonomous systems or routes which have identical properties
 regarding a specific policy.  To make working with such groups easier
 RPSL allows to combine them in set objects.  There are two basic
 types of predefined set objects, as-set, and route-set.  The RPSL set
 objects are described below.

A.4.1 AS-SET Object

 Autonomous system set objects (as-set) are used to group autonomous
 system objects into named sets.  An as-set has an RPSL name that
 starts with "AS-".  In the example in Figure 17, an as-set called
 AS-NERO-PARTNERS and containing AS3701, AS4201, AS3582, AS4222,
 AS1798 is defined.  The as-set is the RPSL replacement for the RIPE-
 181 as-macro.  It has been extended to include ASes in the set
 indirectly by referencing as set names in the aut-num objects.
 AS-SETs are particularly useful when specifying policies for groups
 such as customers, providers, or for transit.  You are encouraged to
 register sets for these groups because it is most likely that you
 will treat them alike, i.e. you will have a very similar routing
 policy for all your customers which have an autonomous system of
 their own.  You may as well discover that this is also true for the
 providers you are peering with, and it is most convenient to have the
 ASes combined in one as-set for which you offer transit.  For
 example, if a transit provider specifies its import policy using its
 customer's as-set (i.e., its import clause for the customer contains
 the customer's as-set), then that customer can modify the set of ASes
 that its transit provider accepts from it.  Again, this can be
 accomplished without requiring the customer or the transit provider
 to modify its aut-num object.
    as-set:    AS3582:AS-PARTNERS
    members:   AS3701, AS4201, AS3582, AS4222, AS1798
                        Figure 17:  as-set Object

Meyer, et al. Informational [Page 21] RFC 2650 Using RPSL in Practice August 1999

 The ASes of the set are simply compiled in a comma delimited list
 following the members attribute of the as-set.  This list may also
 contain other AS-SET names.

A.4.2 ROUTE-SET Object

 A route-set is a way to name a group of routes.  The syntax is
 similar to the as-set.  A route-set has an RPSL name that starts with
 "RS-".  The members attribute lists the members of the set.  The
 value of a members attribute is a list of address prefixes, or
 route-set names.  The members of the route-set are the address
 prefixes or the names of other route sets specified.
 Figure 18 presents some example route-set objects.  The set rs-uo
 contains two address prefixes, namely 128.223.0.0/16 and
 198.32.162.0/24.  The set rs-bar contains the members of the set rs-
 uo and the address prefix 128.7.0.0/16.  The set rs-martians
 illustrate the use of range operators.  0.0.0.0/0^32 are the length
 32 more specifics of 0.0.0.0/0, i.e. the host routes; 224.0.0.0/3^+
 are the more specifics of 224.0.0.0/3, i.e. the routes falling into
 the multicast address space.  For more complete list of range
 operators please refer to RFC-2622.
    route-set: rs-uo
    members: 128.223.0.0/16, 198.32.162.0/24
    route-set: rs-bar
    members: 128.7.0.0/16, rs-uo
    route-set: rs-martians
    remarks: routes not accepted from any peer
    members: 0.0.0.0/0,              # default route
             0.0.0.0/0^32,           # host routes
             224.0.0.0/3^+,          # multicast routes
             127.0.0.0/8^9-32, . . .
                      Figure 18:  route-set Objects

Meyer, et al. Informational [Page 22] RFC 2650 Using RPSL in Practice August 1999

B Output of RtConfig: An Example

    In Figure 19, you see the result of running RtConfig on the source
    file in Figure 11.
    router    bgp 3582
    network   128.223.0.0
    !
    !       NERO
    neighbor 198.32.162.2 remote-as 3701
    no access-list 100
    access-list 100 permit ip 128.223.0.0   0.0.0.0   255.255.0.0   0.0.0.0
    access-list 100 deny ip 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255
    !
    no route-map AS3701-EXPORT
    route-map AS3701-EXPORT permit 1
     match ip address 100
    !
    router bgp 3582
    neighbor 198.32.162.2 route-map AS3701-EXPORT out
    !
    no route-map AS3701-IMPORT
    route-map AS3701-IMPORT permit 1
     set local-preference 1000
    !
    router bgp 3582
    neighbor 198.32.162.2 route-map AS3701-IMPORT in
    !
    !       WNA/VERIO
    neighbor 198.32.162.6 remote-as 2914
    !
    no route-map AS2914-EXPORT
    route-map AS2914-EXPORT permit 1
     match ip address 100
    !
    router bgp 3582
    neighbor 198.32.162.6 route-map AS2914-EXPORT out
    no ip as-path access-list  100
    ip as-path access-list 100 permit ^_2914(((_[0-9]+))*_             \
          (13|22|97|132|175|668|1914|2905|2914|3361|3381|3791|3937|    \
           4178|4354|4571|4674|4683|5091|5303|5798|5855|5856|5881|6083 \
           |6188|6971|7790|7951|8028))?$
    !
    no route-map AS2914-IMPORT
    route-map AS2914-IMPORT permit 1
     match as-path 100
     set local-preference 998

Meyer, et al. Informational [Page 23] RFC 2650 Using RPSL in Practice August 1999

    !
    router bgp 3582
    neighbor 198.32.162.6 route-map AS2914-IMPORT in
                      Figure 19:  Output of RtConfig

Security Considerations

    This document is a tutorial to RPSL, it does not define protocols or
    standards that need to be secured.

Endnotes

 (1) AS-PATH regular expressions are POSIX compliant regular
     expressions.
 (2) Discussion of RtConfig internals is beyond the scope of this
     document.
 (3) Clearly, neither of these mechanisms is sufficient to provide
     strong authentication or authorization.  Other public key (e.g.,
     PGP) authentication mechanisms are available from some of the
     IRRs.

References

 [1] Alaettinoglu, C., Villamizar, C., Gerich, E., Kessens, D., Meyer,
     D., Bates, T., Karrenberg, D. and M. Terpstra, "Routing Policy
     Specification Language (RPSL)", RFC 2622, June 1999.
 [2] Bates, T., Jouanigot, J-M., Karrenberg, D., Lothberg, P. and M.
     Terpstra, "Representation of IP Routing Policies in the RIPE
     database", Technical Report ripe-81, RIPE, RIPE NCC, Amsterdam,
     Netherlands, February 1993.
 [3] T. Bates, E. Gerich, J. Joncharay, J-M. Jouanigot, D. Karrenberg,
     M.  Terpstra, and J. Yu. Representation of IP Routing Policies in
     a Routing Registry, Technical Report ripe-181, RIPE, RIPE NCC,
     Amsterdam, Netherlands, October 1994.
 [4] A. M. R. Magee. RIPE NCC Database Documentation. Technical Report
     RIPE-157, RIPE NCC, Amsterdam, Netherlands, May 1997.
 [5] Hank Nussbacher. The CIDR FAQ. Tel Aviv University and IBM
     Israel.  http://www.ibm.net.il/~hank/cidr.html
 [6] The RAToolSet. http://www.ra.net/ra/RAToolSet/

Meyer, et al. Informational [Page 24] RFC 2650 Using RPSL in Practice August 1999

 [7] Rekhter Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)", RFC
     1654, July 1994.
 [8] RtConfig as part of the RAToolSet.
     http://www.ra.net/ra/RAToolSet/RtConfig.html
 [9] Chen, E. and T. Bates, "An Application of the BGP Community
     Attribute in Multi-Home Routing", RFC 1998, August 1996.

Authors' Addresses

 David Meyer
 Cisco Systems
 EMail: dmm@cisco.com
 Joachim Schmitz
 America On-Line
 EMail: SchmitzJo@aol.com
 Carol Orange
 RIPE NCC
 EMail: orange@spiritone.com
 Mark Prior
 connect.com.au pty ltd
 EMail: mrp@connect.com.au
 Cengiz Alaettinoglu
 USC/Information Sciences Institute
 EMail: cengiz@isi.edu

Meyer, et al. Informational [Page 25] RFC 2650 Using RPSL in Practice August 1999

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.

Meyer, et al. Informational [Page 26]

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