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RFC 2622

 
 
 

Routing Policy Specification Language (RPSL)

Part 2 of 3, p. 27 to 52
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6 aut-num Class

   Routing policies are specified using the aut-num class.  The
   attributes of the aut-num class are shown in Figure 23.  The value of
   the aut-num attribute is the AS number of the AS described by this
   object.  The as-name attribute is a symbolic name (in RPSL name
   syntax) of the AS. The import, export and default routing policies of
   the AS are specified using import, export and default attributes
   respectively.

   Attribute  Value                  Type
   aut-num    <as-number>            mandatory, single-valued, class key
   as-name    <object-name>          mandatory, single-valued
   member-of  list of <as-set-names> optional, multi-valued
   import     see Section 6.1        optional, multi valued
   export     see Section 6.2        optional, multi valued
   default    see Section 6.5        optional, multi valued

                    Figure 23:  aut-num Class Attributes

6.1 import Attribute:  Import Policy Specification

   In RPSL, an import policy is divided into import policy expressions.
   Each import policy expression is specified using an import attribute.
   The import attribute has the following syntax (we will extend this
   syntax later in Sections 6.3 and 6.6):

   import: from <peering-1> [action <action-1>]
            . . .
            from <peering-N> [action <action-N>]
            accept <filter>

   The action specification is optional.  The semantics of an import
   attribute is as follows: the set of routes that are matched by
   <filter> are imported from all the peers in <peerings>; while
   importing routes at <peering-M>, <action-M> is executed.

  E.g.
    aut-num: AS1
    import: from AS2 action pref = 1; accept { 128.9.0.0/16 }

   This example states that the route 128.9.0.0/16 is accepted from AS2
   with preference 1.  We already presented how peerings (see Section
   5.6) and filters (see Section 5.4) are specified.  We next present
   how to specify actions.

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6.1.1 Action Specification

   Policy actions in RPSL either set or modify route attributes, such as
   assigning a preference to a route, adding a BGP community to the BGP
   community path attribute, or setting the MULTI-EXIT-DISCRIMINATOR
   attribute.  Policy actions can also instruct routers to perform
   special operations, such as route flap damping.

   The routing policy attributes whose values can be modified in policy
   actions are specified in the RPSL dictionary.  Please refer to
   Section 7 for a list of these attributes.  Each action in RPSL is
   terminated by the semicolon character (';').  It is possible to form
   composite policy actions by listing them one after the other.  In a
   composite policy action, the actions are executed left to right.  For
   example,

 aut-num: AS1
 import: from AS2
         action pref = 10; med = 0; community.append(10250, 3561:10);
         accept { 128.9.0.0/16 }

   sets pref to 10, med to 0, and then appends 10250 and 3561:10 to the
   BGP community path attribute.  The pref attribute is the inverse of
   the local-pref attribute (i.e. local-pref == 65535 - pref).  A route
   with a local-pref attribute is always preferred over a route without
   one.

 aut-num: AS1
 import: from AS2 action pref = 1;
         from AS3 action pref = 2;
         accept AS4

   The above example states that AS4's routes are accepted from AS2 with
   preference 1, and from AS3 with preference 2 (routes with lower
   integer preference values are preferred over routes with higher
   integer preference values).

 aut-num: AS1
 import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 1;
         from AS2                    action pref = 2;
         accept AS4

   The above example states that AS4's routes are accepted from AS2 on
   peering 7.7.7.1-7.7.7.2 with preference 1, and on any other peering
   with AS2 with preference 2.

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6.2 export Attribute:  Export Policy Specification

   Similarly, an export policy expression is specified using an export
   attribute.  The export attribute has the following syntax:

    export: to <peering-1> [action <action-1>]
            . . .
            to <peering-N> [action <action-N>]
            announce <filter>

   The action specification is optional.  The semantics of an export
   attribute is as follows:  the set of routes that are matched by
   <filter> are exported to all the peers specified in <peerings>; while
   exporting routes at <peering-M>, <action-M> is executed.

  E.g.
    aut-num: AS1
    export: to AS2 action med = 5; community .= { 70 };
            announce AS4

   In this example, AS4's routes are announced to AS2 with the med
   attribute's value set to 5 and community 70 added to the community
   list.

   Example:

    aut-num: AS1
    export: to AS-FOO announce ANY

   In this example, AS1 announces all of its routes to the ASes in the
   set AS-FOO.

6.3 Other Routing Protocols, Multi-Protocol Routing Protocols, and
   Injecting Routes Between Protocols

   The more complete syntax of the import and export attributes are as
   follows:

    import: [protocol <protocol-1>] [into <protocol-2>]
            from <peering-1> [action <action-1>]
            . . .
            from <peering-N> [action <action-N>]
            accept <filter>
    export: [protocol <protocol-1>] [into <protocol-2>]
            to <peering-1> [action <action-1>]
            . . .
            to <peering-N> [action <action-N>]
            announce <filter>

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   Where the optional protocol specifications can be used for specifying
   policies for other routing protocols, or for injecting routes of one
   protocol into another protocol, or for multi-protocol routing
   policies.  The valid protocol names are defined in the dictionary.
   The <protocol-1> is the name of the protocol whose routes are being
   exchanged.  The <protocol-2> is the name of the protocol which is
   receiving these routes.  Both <protocol-1> and <protocol-2> default
   to the Internet Exterior Gateway Protocol, currently BGP.

   In the following example, all interAS routes are injected into RIP.

 aut-num: AS1
 import: from AS2 accept AS2
 export: protocol BGP4 into RIP
         to AS1 announce ANY

   In the following example, AS1 accepts AS2's routes including any more
   specifics of AS2's routes, but does not inject these extra more
   specific routes into OSPF.

 aut-num: AS1
 import: from AS2 accept AS2^+
 export: protocol BGP4 into OSPF
         to AS1 announce AS2

   In the following example, AS1 injects its static routes (routes which
   are members of the set AS1:RS-STATIC-ROUTES) to the interAS routing
   protocol and appends AS1 twice to their AS paths.

 aut-num: AS1
 import: protocol STATIC into BGP4
         from AS1 action aspath.prepend(AS1, AS1);
         accept AS1:RS-STATIC-ROUTES

   In the following example, AS1 imports different set of unicast routes
   for multicast reverse path forwarding from AS2:

 aut-num: AS1
 import: from AS2 accept AS2
 import: protocol IDMR
         from AS2 accept AS2:RS-RPF-ROUTES

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6.4 Ambiguity Resolution

   It is possible that the same peering can be covered by more that one
   peering specification in a policy expression.  For example:

 aut-num: AS1
 import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 2;
         from AS2 7.7.7.2 at 7.7.7.1 action pref = 1;
         accept AS4

   This is not an error, though definitely not desirable.  To break the
   ambiguity, the action corresponding to the first peering
   specification is used.  That is the routes are accepted with
   preference 2.  We call this rule as the specification-order rule.

   Consider the example:

 aut-num: AS1
 import: from AS2                    action pref = 2;
         from AS2 7.7.7.2 at 7.7.7.1 action pref = 1; dpa = 5;
         accept AS4

   where both peering specifications cover the peering 7.7.7.1-7.7.7.2,
   though the second one covers it more specifically.  The specification
   order rule still applies, and only the action "pref = 2" is executed.
   In fact, the second peering-action pair has no use since the first
   peering-action pair always covers it.  If the intended policy was to
   accept these routes with preference 1 on this particular peering and
   with preference 2 in all other peerings, the user should have
   specified:

 aut-num: AS1
 import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 1; dpa = 5;
         from AS2                    action pref = 2;
         accept AS4

   It is also possible that more than one policy expression can cover
   the same set of routes for the same peering.  For example:

 aut-num: AS1
 import: from AS2 action pref = 2; accept AS4
 import: from AS2 action pref = 1; accept AS4

   In this case, the specification-order rule is still used.  That is,
   AS4's routes are accepted from AS2 with preference 2.  If the filters
   were overlapping but not exactly the same:

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 aut-num: AS1
 import: from AS2 action pref = 2; accept AS4
 import: from AS2 action pref = 1; accept AS4 OR AS5

   the AS4's routes are accepted from AS2 with preference 2 and however
   AS5's routes are also accepted, but with preference 1.

   We next give the general specification order rule for the benefit of
   the RPSL implementors.  Consider two policy expressions:

 aut-num: AS1
 import: from peerings-1 action action-1 accept filter-1
 import: from peerings-2 action action-2 accept filter-2

   The above policy expressions are equivalent to the following three
   expressions where there is no ambiguity:

 aut-num: AS1
 import: from peerings-1 action action-1 accept filter-1
 import: from peerings-3 action action-2 accept filter-2 AND NOT filter-1
 import: from peerings-4 action action-2 accept filter-2

   where peerings-3 are those that are covered by both peerings-1 and
   peerings-2, and peerings-4 are those that are covered by peerings-2
   but not by peerings-1 ("filter-2 AND NOT filter-1" matches the routes
   that are matched by filter-2 but not by filter-1).

   Example:

 aut-num: AS1
 import: from AS2 7.7.7.2 at 7.7.7.1
         action pref = 2;
         accept {128.9.0.0/16}
 import: from AS2
         action pref = 1;
         accept {128.9.0.0/16, 75.0.0.0/8}

   Lets consider two peerings with AS2, 7.7.7.1-7.7.7.2 and 9.9.9.1-
   9.9.9.2.  Both policy expressions cover 7.7.7.1-7.7.7.2.  On this
   peering, the route 128.9.0.0/16 is accepted with preference 2, and
   the route 75.0.0.0/8 is accepted with preference 1.  The peering
   9.9.9.1-9.9.9.2 is only covered by the second policy expressions.
   Hence, both the route 128.9.0.0/16 and the route 75.0.0.0/8 are
   accepted with preference 1 on peering 9.9.9.1-9.9.9.2.

   Note that the same ambiguity resolution rules also apply to export
   and default policy expressions.

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6.5 default Attribute:  Default Policy Specification

   Default routing policies are specified using the default attribute.
   The default attribute has the following syntax:

    default: to <peering> [action <action>] [networks <filter>]

   The <action> and <filter> specifications are optional.  The semantics
   are as follows:  The <peering> specification indicates the AS (and
   the router if present) is being defaulted to; the <action>
   specification, if present, indicates various attributes of
   defaulting, for example a relative preference if multiple defaults
   are specified; and the <filter> specifications, if present, is a
   policy filter.  A router only uses the default policy if it received
   the routes matched by <filter> from this peer.

   In the following example, AS1 defaults to AS2 for routing.

 aut-num: AS1
 default: to AS2

   In the following example, router 7.7.7.1 in AS1 defaults to router
   7.7.7.2 in AS2.

 aut-num: AS1
 default: to AS2 7.7.7.2 at 7.7.7.1

   In the following example, AS1 defaults to AS2 and AS3, but prefers
   AS2 over AS3.

 aut-num: AS1
 default: to AS2 action pref = 1;
 default: to AS3 action pref = 2;

   In the following example, AS1 defaults to AS2 and uses 128.9.0.0/16
   as the default network.

 aut-num: AS1
 default: to AS2 networks { 128.9.0.0/16 }

6.6 Structured Policy Specification

   The import and export policies can be structured.  We only reccomend
   structured policies to advanced RPSL users.  Please feel free to skip
   this section.

   The syntax for a structured policy specification is the following:

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   <import-factor> ::= from <peering-1> [action <action-1>]
                       . . .
                       from <peering-N> [action <action-N>]
                       accept <filter>;

   <import-term> ::=  <import-factor> |
                      LEFT-BRACE
                      <import-factor>
                      . . .
                      <import-factor>
                      RIGHT-BRACE

   <import-expression> ::= <import-term>                            |
                           <import-term> EXCEPT <import-expression> |
                           <import-term> REFINE <import-expression>

   import: [protocol <protocol1>] [into <protocol2>]
           <import-expression>

   Please note the semicolon at the end of an <import-factor>.  If the
   policy specification is not structured (as in all the examples in
   other sections), this semicolon is optional.  The syntax and
   semantics for an <import-factor> is already defined in Section 6.1.

   An <import-term> is either a sequence of <import-factor>'s enclosed
   within matching braces (i.e. `{' and `}') or just a single <import-
   factor>.  The semantics of an <import-term> is the union of <import-
   factor>'s using the specification order rule.  An <import-expression>
   is either a single <import-term> or an <import-term> followed by one
   of the keywords "except" and "refine", followed by another <import-
   expression>.  Note that our definition allows nested expressions.
   Hence there can be exceptions to exceptions, refinements to
   refinements, or even refinements to exceptions, and so on.

   The semantics for the except operator is as follows: The result of an
   except operation is another <import-term>.  The resulting policy set
   contains the policies of the right hand side but their filters are
   modified to only include the routes also matched by the left hand
   side.  The policies of the left hand side are included afterwards and
   their filters are modified to exclude the routes matched by the right
   hand side.  Please note that the filters are modified during this
   process but the actions are copied verbatim.  When there are multiple
   levels of nesting, the operations (both except and refine) are
   performed right to left.

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   Consider the following example:

 import: from AS1 action pref = 1; accept as-foo;
         except {
            from AS2 action pref = 2; accept AS226;
            except {
               from AS3 action pref = 3; accept {128.9.0.0/16};
            }
         }

   where the route 128.9.0.0/16 is originated by AS226, and AS226 is a
   member of the as set as-foo.  In this example, the route 128.9.0.0/16
   is accepted from AS3, any other route (not 128.9.0.0/16) originated
   by AS226 is accepted from AS2, and any other ASes' routes in as-foo
   is accepted from AS1.

   We can come to the same conclusion using the algebra defined above.
   Consider the inner exception specification:

   from AS2 action pref = 2; accept AS226;
   except {
      from AS3 action pref = 3; accept {128.9.0.0/16};
   }


 is equivalent to


  {
   from AS3 action pref = 3; accept AS226 AND {128.9.0.0/16};
   from AS2 action pref = 2; accept AS226 AND NOT {128.9.0.0/16};
  }


 Hence, the original expression is equivalent to:


 import: from AS1 action pref = 1; accept as-foo;
         except {
            from AS3 action pref = 3; accept AS226 AND {128.9.0.0/16};
            from AS2 action pref = 2; accept AS226 AND NOT {128.9.0.0/16};
         }


 which is equivalent to


import: {

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   from AS3 action pref = 3;
            accept as-foo AND AS226 AND {128.9.0.0/16};
   from AS2 action pref = 2;
            accept as-foo AND AS226 AND NOT {128.9.0.0/16};
   from AS1 action pref = 1;
            accept as-foo AND NOT
              (AS226 AND NOT {128.9.0.0/16} OR AS226 AND {128.9.0.0/16});
   }


 Since AS226 is in as-foo and 128.9.0.0/16 is in AS226, it simplifies
 to:


import: {
          from AS3 action pref = 3; accept {128.9.0.0/16};
          from AS2 action pref = 2; accept AS226 AND NOT {128.9.0.0/16};
          from AS1 action pref = 1; accept as-foo AND NOT AS226;
        }

   In the case of the refine operator, the resulting set is constructed
   by taking the cartasian product of the two sides as follows:  for
   each policy l in the left hand side and for each policy r in the
   right hand side, the peerings of the resulting policy are the
   peerings common to both r and l; the filter of the resulting policy
   is the intersection of l's filter and r's filter; and action of the
   resulting policy is l's action followed by r's action.  If there are
   no common peerings, or if the intersection of filters is empty, a
   resulting policy is not generated.

   Consider the following example:

 import: { from AS-ANY action pref = 1; accept community(3560:10);
           from AS-ANY action pref = 2; accept community(3560:20);
         } refine {
            from AS1 accept AS1;
            from AS2 accept AS2;
            from AS3 accept AS3;
         }

   Here, any route with community 3560:10 is assigned a preference of 1
   and any route with community 3560:20 is assigned a preference of 2
   regardless of whom they are imported from.  However, only AS1's
   routes are imported from AS1, and only AS2's routes are imported from
   AS2, and only AS3's routes are imported form AS3, and no routes are
   imported from any other AS. We can reach the same conclusion using
   the above algebra.  That is, our example is equivalent to:

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 import: {
   from AS1 action pref = 1; accept community(3560:10) AND AS1;
   from AS1 action pref = 2; accept community(3560:20) AND AS1;
   from AS2 action pref = 1; accept community(3560:10) AND AS2;
   from AS2 action pref = 2; accept community(3560:20) AND AS2;
   from AS3 action pref = 1; accept community(3560:10) AND AS3;
   from AS3 action pref = 2; accept community(3560:20) AND AS3;
 }

   Note that the common peerings between "from AS1" and "from AS-ANY"
   are those peerings in "from AS1".  Even though we do not formally
   define "common peerings", it is straight forward to deduce the
   definition from the definitions of peerings (please see Section 5.6).

   Consider the following example:

 import: {
   from AS-ANY action med = 0; accept {0.0.0.0/0^0-18};
   } refine {
        from AS1 at 7.7.7.1 action pref = 1; accept AS1;
        from AS1            action pref = 2; accept AS1;
     }

   where only routes of length 0 to 18 are accepted and med's value is
   set to 0 to disable med's effect for all peerings; In addition, from
   AS1 only AS1's routes are imported, and AS1's routes imported at
   7.7.7.1 are preferred over other peerings.  This is equivalent to:

 import: {
      from AS1 at 7.7.7.1 action med=0; pref=1; accept {0.0.0.0/0^0-
18} AND AS1;
    from  AS1             action med=0; pref=2; accept {0.0.0.0/0^0-
18} AND AS1;
 }

   The above syntax and semantics also apply equally to structured
   export policies with "from" replaced with "to" and "accept" is
   replaced with "announce".

7 dictionary Class

   The dictionary class provides extensibility to RPSL. Dictionary
   objects define routing policy attributes, types, and routing
   protocols.  Routing policy attributes, henceforth called rp-
   attributes, may correspond to actual protocol attributes, such as the
   BGP path attributes (e.g. community, dpa, and AS-path), or they may
   correspond to router features (e.g. BGP route flap damping).  As new
   protocols, new protocol attributes, or new router features are

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   introduced, the dictionary object is updated to include appropriate
   rp-attribute and protocol definitions.

   An rp-attribute is an abstract class; that is a data representation
   is not available.  Instead, they are accessed through access methods.
   For example, the rp-attribute for the BGP AS-path attribute is called
   aspath; and it has an access method called prepend which stuffs extra
   AS numbers to the AS-path attributes.  Access methods can take
   arguments.  Arguments are strongly typed.  For example, the method
   prepend above takes AS numbers as arguments.

   Once an rp-attribute is defined in the dictionary, it can be used to
   describe policy filters and actions.  Policy analysis tools are
   required to fetch the dictionary object and recognize newly defined
   rp-attributes, types, and protocols.  The analysis tools may
   approximate policy analyses on rp-attributes that they do not
   understand:  a filter method may always match, and an action method
   may always perform no-operation.  Analysis tools may even download
   code to perform appropriate operations using mechanisms outside the
   scope of RPSL.

   We next describe the syntax and semantics of the dictionary class.
   This description is not essential for understanding dictionary
   objects (but it is essential for creating one).  Please feel free to
   skip to the RPSL Initial Dictionary subsection (Section 7.1).

   The attributes of the dictionary class are shown in Figure 24.  The
   dictionary attribute is the name of the dictionary object, obeying
   the RPSL naming rules.  There can be many dictionary objects, however
   there is always one well-known dictionary object "RPSL". All tools
   use this dictionary by default.

 Attribute     Value                   Type
 dictionary    <object-name>           mandatory, single-valued,
                                       class key
 rp-attribute  see description in text optional, multi valued
 typedef       see description in text optional, multi valued
 protocol      see description in text optional, multi valued

                  Figure 24:  dictionary Class Attributes

   The rp-attribute attribute has the following syntax:

   rp-attribute: <name>
      <method-1>(<type-1-1>, ..., <type-1-N1> [, "..."])
      ...
      <method-M>(<type-M-1>, ..., <type-M-NM> [, "..."])

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   where <name> is the name of the rp-attribute; and <method-i> is the
   name of an access method for the rp-attribute, taking Ni arguments
   where the j-th argument is of type <type-i-j>.  A method name is
   either an RPSL name or one of the operators defined in Figure 25.
   The operator methods with the exception of operator() and operator[]
   can take only one argument.

   operator=           operator==
   operator<<=         operator<
   operator>>=         operator>
   operator+=          operator>=
   operator-=          operator<=
   operator*=          operator!=
   operator/=          operator()
   operator.=          operator[]


                           Figure 25:  Operators

   An rp-attribute can have many methods defined for it.  Some of the
   methods may even have the same name, in which case their arguments
   are of different types.  If the argument list is followed by "...",
   the method takes a variable number of arguments.  In this case, the
   actual arguments after the Nth argument are of type <type-N>.

   Arguments are strongly typed.  A <type> in RPSL is either a
   predefined type, a union type, a list type, or a dictionary defined
   type.  The predefined types are listed in Figure 26.

   integer[lower, upper]              ipv4_address
   real[lower, upper]                 address_prefix
   enum[name, name, ...]              address_prefix_range
   string                             dns_name
   boolean                            filter
   rpsl_word                          as_set_name
   free_text                          route_set_name
   email                              rtr_set_name
   as_number                          filter_set_name
                                      peering_set_name


                        Figure 26:  Predefined Types

   The integer and the real predefined types can be followed by a lower
   and an upper bound to specify the set of valid values of the
   argument.  The range specification is optional.  We use the ANSI C
   language conventions for representing integer, real and string
   values.  The enum type is followed by a list of RPSL names which are

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   the valid values of the type.  The boolean type can take the values
   true or false.  as_number, ipv4_address, address_prefix and dns_name
   types are as in Section 2.  filter type is a policy filter as in
   Section 6.  The value of filter type is suggested to be enclosed in
   parenthesis.

   The syntax of a union type is as follows:

    union <type-1>, ... , <type-N>

   where <type-i> is an RPSL type.  The union type is either of the
   types <type-1> through <type-N> (analogous to unions in C[14]).

   The syntax of a list type is as follows:

   list [<min_elems>:<max_elems>] of <type>

   In this case, the list elements are of <type> and the list contains
   at least <min_elems> and at most <max_elems> elements.  The size
   specification is optional.  If it is not specified, there is no
   restriction in the number of list elements.  A value of a list type
   is represented as a sequence of elements separated by the character
   "," and enclosed by the characters "{" and "}".

   The typedef attribute in the dictionary defines named types as
   follows:

   typedef: <name> <type>

   where <name> is a name for type <type>.  typedef attribute is
   paticularly useful when the type defined is not a predefined type
   (e.g. list of unions, list of lists, etc.).

   A protocol attribute of the dictionary class defines a protocol and a
   set of peering parameters for that protocol (which are used in inet-
   rtr class in Section 9).  Its syntax is as follows:

   protocol: <name>
    MANDATORY | OPTIONAL <parameter-1>(<type-1-1>,...,
                         <type-1-N1> [,"..."])
      ...
    MANDATORY | OPTIONAL <parameter-M>(<type-M-1>,...,
                         <type-M-NM> [,"..."])

   where <name> is the name of the protocol; MANDATORY and OPTIONAL are
   keywords; and <parameter-i> is a peering parameter for this protocol,
   taking Ni many arguments.  The syntax and semantics of the arguments
   are as in the rp-attribute.  If the keyword MANDATORY is used, the

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   parameter is mandatory and needs to be specified for each peering of
   this protocol.  If the keyword OPTIONAL is used, the parameter can be
   skipped.

7.1 Initial RPSL Dictionary and Example Policy Actions and Filters

dictionary:   RPSL
rp-attribute: # preference, smaller values represent higher preferences
              pref
              operator=(integer[0, 65535])
rp-attribute: # BGP multi_exit_discriminator attribute
              med
              # to set med to 10: med = 10;
              # to set med to the IGP metric: med = igp_cost;
              operator=(union integer[0, 65535], enum[igp_cost])
rp-attribute: # BGP destination preference attribute (dpa)
              dpa
              operator=(integer[0, 65535])
rp-attribute: # BGP aspath attribute
              aspath
              # prepends AS numbers from last to first order
              prepend(as_number, ...)
typedef:      # a community value in RPSL is either
              #  - a 4 byte integer (ok to use 3561:70 notation)
              #  - internet, no_export, no_advertise (see RFC-1997)
              community_elm union
                  integer[1, 4294967295],
                  enum[internet, no_export, no_advertise],
typedef:      # list of community values { 40, no_export, 3561:70 }
              community_list list of community_elm
rp-attribute: # BGP community attribute
              community
              # set to a list of communities
              operator=(community_list)
              # append community values
              operator.=(community_list)
              append(community_elm, ...)
              # delete community values
              delete(community_elm, ...)
              # a filter: true if one of community values is contained
              contains(community_elm, ...)
              # shortcut to contains: community(no_export, 3561:70)
              operator()(community_elm, ...)
              # order independent equality comparison
              operator==(community_list)
rp-attribute: # next hop router in a static route
              next-hop
              # to set to 7.7.7.7: next-hop = 7.7.7.7;

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              # to set to router's own address: next-hop = self;
              operator=(union ipv4_address, enum[self])
rp-attribute: # cost of a static route
              cost
              operator=(integer[0, 65535])
protocol: BGP4
          # as number of the peer router
          MANDATORY asno(as_number)
          # enable flap damping
          OPTIONAL flap_damp()
          OPTIONAL flap_damp(integer[0,65535],
                             # penalty per flap
                             integer[0,65535],
                             # penalty value for supression
                             integer[0,65535],
                             # penalty value for reuse
                             integer[0,65535],
                             # halflife in secs when up
                             integer[0,65535],
                             # halflife in secs when down
                             integer[0,65535])
                             # maximum penalty
protocol: OSPF
protocol: RIP
protocol: IGRP
protocol: IS-IS
protocol: STATIC
protocol: RIPng
protocol: DVMRP
protocol: PIM-DM
protocol: PIM-SM
protocol: CBT
protocol: MOSPF


                        Figure 27:  RPSL Dictionary

   Figure 27 shows the initial RPSL dictionary.  It has seven rp-
   attributes:  pref to assign local preference to the routes accepted;
   med to assign a value to the MULTI_EXIT_DISCRIMINATOR BGP attribute;
   dpa to assign a value to the DPA BGP attribute; aspath to prepend a
   value to the AS_PATH BGP attribute; community to assign a value to or
   to check the value of the community BGP attribute; next-hop to assign
   next hop routers to static routes; and cost to assign a cost to
   static routes.  The dictionary defines two types:  community_elm and
   community_list.  community_elm type is either a 4-byte unsigned
   integer, or one of the keywords internet, no_export or no_advertise
   (defined in [9]).  An integer can be specified using two 2-byte

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   integers seperated by ":"  to partition the community number space so
   that a provider can use its AS number as the first two bytes, and
   assigns a semantics of its choice to the last two bytes.

   The initial dictionary (Figure 27) defines only options for the
   Border Gateway Protocol:  asno and flap_damp.  The mandatory asno
   option is the AS number of the peer router.  The optional flap_damp
   option instructs the router to damp route flaps [21] when importing
   routes from the peer router.

   It can be specified with or without parameters.  If parameters are
   missing, they default to:

   flap_damp(1000, 2000, 750, 900, 900, 20000)

   That is, a penalty of 1000 is assigned at each route flap, the route
   is suppressed when penalty reaches 2000.  The penalty is reduced in
   half after 15 minutes (900 seconds) of stability regardless of
   whether the route is up or down.  A supressed route is reused when
   the penalty falls below 750.  The maximum penalty a route can be
   assigned is 20,000 (i.e. the maximum suppress time after a route
   becomes stable is about 75 minutes).  These parameters are consistent
   with the default flap damping parameters in several routers.

Policy Actions and Filters Using RP-Attributes

   The syntax of a policy action or a filter using an rp-attribute x is
   as follows:

    x.method(arguments)
    x "op" argument

   where method is a method and "op" is an operator method of the rp-
   attribute x.  If an operator method is used in specifying a composite
   policy filter, it evaluates earlier than the composite policy filter
   operators (i.e. AND, OR, NOT, and implicit or operator).

   The pref rp-attribute can be assigned a positive integer as follows:

   pref = 10;

   The med rp-attribute can be assigned either a positive integer or the
   word "igp_cost" as follows:

   med = 0;
   med = igp_cost;

   The dpa rp-attribute can be assigned a positive integer as follows:

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   dpa = 100;

   The BGP community attribute is list-valued, that is it is a list of
   4-byte integers each representing a "community".  The following
   examples demonstrate how to add communities to this rp-attribute:

   community .= { 100 };
   community .= { NO_EXPORT };
   community .= { 3561:10 };

   In the last case, a 4-byte integer is constructed where the more
   significant two bytes equal 3561 and the less significant two bytes
   equal 10.  The following examples demonstrate how to delete
   communities from the community rp-attribute:

   community.delete(100, NO_EXPORT, 3561:10);

   Filters that use the community rp-attribute can be defined as
   demonstrated by the following examples:

   community.contains(100, NO_EXPORT, 3561:10);
   community(100, NO_EXPORT, 3561:10);             # shortcut

   The community rp-attribute can be set to a list of communities as
   follows:

   community = {100, NO_EXPORT, 3561:10, 200};
   community = {};

   In this first case, the community rp-attribute contains the
   communities 100, NO_EXPORT, 3561:10, and 200.  In the latter case,
   the community rp-attribute is cleared.  The community rp-attribute
   can be compared against a list of communities as follows:

   community == {100, NO_EXPORT, 3561:10, 200};   # exact match

   To influence the route selection, the BGP as_path rp-attribute can be
   made longer by prepending AS numbers to it as follows:

   aspath.prepend(AS1);
   aspath.prepend(AS1, AS1, AS1);

   The following examples are invalid:

   med = -50;                     # -50 is not in the range
   med = igp;                     # igp is not one of the enum values
   med.assign(10);                # method assign is not defined
   community.append(AS3561:20);   # the first argument should be 3561

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   Figure 28 shows a more advanced example using the rp-attribute
   community.  In this example, AS3561 bases its route selection
   preference on the community attribute.  Other ASes may indirectly
   affect AS3561's route selection by including the appropriate
   communities in their route announcements.

    aut-num: AS1
    export: to AS2 action community.={3561:90};
            to AS3 action community.={3561:80};
            announce AS1

    as-set: AS3561:AS-PEERS
    members: AS2, AS3

    aut-num: AS3561
    import: from AS3561:AS-PEERS
            action pref = 10;
            accept community(3561:90)
    import: from AS3561:AS-PEERS
            action pref = 20;
            accept community(3561:80)
    import: from AS3561:AS-PEERS
            action pref = 20;
            accept community(3561:70)
    import: from AS3561:AS-PEERS
            action pref = 0;
            accept ANY


           Figure 28:  Policy example using the community rp-attribute.

8 Advanced route Class

8.1 Specifying Aggregate Routes

   The components, aggr-bndry, aggr-mtd, export-comps, inject, and holes
   attributes are used for specifying aggregate routes [11].  A route
   object specifies an aggregate route if any of these attributes, with
   the exception of inject, is specified.  The origin attribute for an
   aggregate route is the AS performing the aggregation, i.e. the
   aggregator AS. In this section, we used the term "aggregate" to refer
   to the route generated, the term "component" to refer to the routes
   used to generate the path attributes of the aggregate, and the term
   "more specifics" to refer to any route which is a more specific of
   the aggregate regardless of whether it was used to form the path
   attributes.

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   The components attribute defines what component routes are used to
   form the aggregate.  Its syntax is as follows:

   components: [ATOMIC] [[<filter>] [protocol <protocol> <filter> ...]]

   where <protocol> is a routing protocol name such as BGP4, OSPF or RIP
   (valid names are defined in the dictionary) and <filter> is a policy
   expression.  The routes that match one of these filters and are
   learned from the corresponding protocol are used to form the
   aggregate.  If <protocol> is omitted, it defaults to any protocol.
   <filter> implicitly contains an "AND" term with the more specifics of
   the aggregate so that only the component routes are selected.  If the
   keyword ATOMIC is used, the aggregation is done atomically [11].  If
   a <filter> is not specified it defaults to more specifics.  If the
   components attribute is missing, all more specifics without the
   ATOMIC keyword is used.

   route: 128.8.0.0/15
   origin: AS1
   components: <^AS2>

   route: 128.8.0.0/15
   origin: AS1
   components: protocol BGP4 {128.8.0.0/16^+}
               protocol OSPF {128.9.0.0/16^+}


                  Figure 29:  Two aggregate route objects.

   Figure 29 shows two route objects.  In the first example, more
   specifics of 128.8.0.0/15 with AS paths starting with AS2 are
   aggregated.  In the second example, some routes learned from BGP and
   some routes learned form OSPF are aggregated.

   The aggr-bndry attribute is an AS expression over AS numbers and sets
   (see Section 5.6).  The result defines the set of ASes which form the
   aggregation boundary.  If the aggr-bndry attribute is missing, the
   origin AS is the sole aggregation boundary.  Outside the aggregation
   boundary, only the aggregate is exported and more specifics are
   suppressed.  However, within the boundary, the more specifics are
   also exchanged.

   The aggr-mtd attribute specifies how the aggregate is generated.  Its
   syntax is as follows:

  aggr-mtd: inbound
          | outbound [<as-expression>]

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   where <as-expression> is an expression over AS numbers and sets (see
   Section 5.6).  If <as-expression> is missing, it defaults to AS-ANY.
   If outbound aggregation is specified, the more specifics of the
   aggregate will be present within the AS and the aggregate will be
   formed at all inter-AS boundaries with ASes in <as-expression> before
   export, except for ASes that are within the aggregating boundary
   (i.e. aggr-bndry is enforced regardless of <as-expression>).  If
   inbound aggregation is specified, the aggregate is formed at all
   inter-AS boundaries prior to importing routes into the aggregator AS.
   Note that <as-expression> can not be specified with inbound
   aggregation.  If aggr-mtd attribute is missing, it defaults to
   "outbound AS-ANY".

   route:      128.8.0.0/15            route:      128.8.0.0/15
   origin:     AS1                     origin:     AS2
   components: {128.8.0.0/15^-}        components: {128.8.0.0/15^-}
   aggr-bndry: AS1 OR AS2              aggr-bndry: AS1 OR AS2
   aggr-mtd:   outbound AS-ANY         aggr-mtd:   outbound AS-ANY


             Figure 30:  Outbound multi-AS aggregation example.

   Figure 30 shows an example of an outbound aggregation.  In this
   example, AS1 and AS2 are coordinating aggregation and announcing only
   the less specific 128.8.0.0/15 to outside world, but exchanging more
   specifics between each other.  This form of aggregation is useful
   when some of the components are within AS1 and some are within AS2.

   When a set of routes are aggregated, the intent is to export only the
   aggregate route and suppress exporting of the more specifics outside
   the aggregation boundary.  However, to satisfy certain policy and
   topology constraints (e.g. a multi-homed component), it is often
   required to export some of the components.  The export-comps
   attribute equals an RPSL filter that matches the more specifics that
   need to be exported outside the aggregation boundary.  If this
   attribute is missing, more specifics are not exported outside the
   aggregation boundary.  Note that, the export-comps filter contains an
   implicit "AND" term with the more specifics of the aggregate.

   Figure 31 shows an example of an outbound aggregation.  In this
   example, the more specific 128.8.8.0/24 is exported outside AS1 in
   addition to the aggregate.  This is useful, when 128.8.8.0/24 is
   multi-homed site to AS1 with some other AS.

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      route:      128.8.0.0/15
      origin:     AS1
      components: {128.8.0.0/15^-}
      aggr-mtd:   outbound AS-ANY
      export-comps: {128.8.8.0/24}


             Figure 31:  Outbound aggregation with export exception.

   The inject attribute specifies which routers perform the aggregation
   and when they perform it.  Its syntax is as follow:

  inject: [at <router-expression>] ...
          [action <action>]
          [upon <condition>]

   where <action> is an action specification (see Section 6.1.1),
   <condition> is a boolean expression described below, and <router-
   expression> is as described in Section 5.6.

   All routers in <router-expression> and in the aggregator AS perform
   the aggregation.  If a <router-expression> is not specified, all
   routers inside the aggregator AS perform the aggregation.  The
   <action> specification may set path attributes of the aggregate, such
   as assign a preferences to the aggregate.

   The upon clause is a boolean condition.  The aggregate is generated
   if and only if this condition is true.  <condition> is a boolean
   expression using the logical operators AND and OR (i.e. operator NOT
   is not allowed) over:

   HAVE-COMPONENTS { list of prefixes }
   EXCLUDE { list of prefixes }
   STATIC

   The list of prefixes in HAVE-COMPONENTS can only be more specifics of
   the aggregate.  It evaluates to true when all the prefixes listed are
   present in the routing table of the aggregating router.  The list can
   also include prefix ranges (i.e. using operators ^-, ^+, ^n, and ^n-
   m).  In this case, at least one prefix from each prefix range needs
   to be present in the routing table for the condition to be true.  The
   list of prefixes in EXCLUDE can be arbitrary.  It evaluates to true
   when none of the prefixes listed is present in the routing table.
   The list can also include prefix ranges, and no prefix in that range
   should be present in the routing table.  The keyword static always
   evaluates to true.  If no upon clause is specified the aggregate is
   generated if an only if there is a component in the routing table
   (i.e. a more specific that matches the filter in the components

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   attribute).

   route:      128.8.0.0/15
   origin:     AS1
   components: {128.8.0.0/15^-}
   aggr-mtd:   outbound AS-ANY
   inject:     at 1.1.1.1 action dpa = 100;
   inject:     at 1.1.1.2 action dpa = 110;

   route:      128.8.0.0/15
   origin:     AS1
   components: {128.8.0.0/15^-}
   aggr-mtd:   outbound AS-ANY
   inject:     upon HAVE-COMPONENTS {128.8.0.0/16, 128.9.0.0/16}
   holes:      128.8.8.0/24


                      Figure 32:  Examples of inject.

   Figure 32 shows two examples.  In the first case, the aggregate is
   injected at two routers each one setting the dpa path attribute
   differently.  In the second case, the aggregate is generated only if
   both 128.8.0.0/16 and 128.9.0.0/16 are present in the routing table,
   as opposed to the first case where the presence of just one of them
   is sufficient for injection.

   The holes attribute lists the component address prefixes which are
   not reachable through the aggregate route (perhaps that part of the
   address space is unallocated).  The holes attribute is useful for
   diagnosis purposes.  In Figure 32, the second example has a hole,
   namely 128.8.8.0/24.  This may be due to a customer changing
   providers and taking this part of the address space with it.

8.1.1 Interaction with policies in aut-num class

   An aggregate formed is announced to other ASes only if the export
   policies of the AS allows exporting the aggregate.  When the
   aggregate is formed, the more specifics are suppressed from being
   exported except to the ASes in aggr-bndry and except the components
   in export-comps.  For such exceptions to happen, the export policies
   of the AS should explicitly allow exporting of these exceptions.

   If an aggregate is not formed (due to the upon clause), then the more
   specifics of the aggregate can be exported to other ASes, but only if
   the export policies of the AS allows it.  In other words, before a
   route (aggregate or more specific) is exported it is filtered twice,
   once based on the route objects, and once based on the export
   policies of the AS.

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   route:        128.8.0.0/16
   origin:       AS1

   route:        128.9.0.0/16
   origin:       AS1

   route:        128.8.0.0/15
   origin:       AS1
   aggr-bndry:   AS1 or AS2 or AS3
   aggr-mtd:     outbound AS3 or AS4 or AS5
   components:   {128.8.0.0/16, 128.9.0.0/16}
   inject:       upon HAVE-COMPONENTS {128.9.0.0/16, 128.8.0.0/16}

   aut-num: AS1
   export:  to AS2 announce AS1
   export:  to AS3 announce AS1 and not {128.9.0.0/16}
   export:  to AS4 announce AS1
   export:  to AS5 announce AS1
   export:  to AS6 announce AS1


          Figure 33:  Interaction with policies in aut-num class.

   In Figure 33 shows an interaction example.  By examining the route
   objects, the more specifics 128.8.0.0/16 and 128.9.0.0/16 should be
   exchanged between AS1, AS2 and AS3 (i.e. the aggregation boundary).
   Outbound aggregation is done to AS4 and AS5 and not to AS3, since AS3
   is in the aggregation boundary.  The aut-num object allows exporting
   both components to AS2, but only the component 128.8.0.0/16 to AS3.
   The aggregate can only be formed if both components are available.
   In this case, only the aggregate is announced to AS4 and AS5.
   However, if one of the components is not available the aggregate will
   not be formed, and any available component or more specific will be
   exported to AS4 and AS5.  Regardless of aggregation is performed or
   not, only the more specifics will be exported to AS6 (it is not
   listed in the aggr-mtd attribute).

   When doing an inbound aggregation, configuration generators may
   eliminating the aggregation statements on routers where import policy
   of the AS prohibits importing of any more specifics.

8.1.2 Ambiguity resolution with overlapping aggregates

   When several aggregate routes are specified and they overlap, i.e.
   one is less specific of the other, they must be evaluated more
   specific to less specific order.  When an outbound aggregation is
   performed for a peer, the aggregate and the components listed in the
   export-comps attribute for that peer are available for generating the

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   next less specific aggregate.  The components that are not specified
   in the export-comps attribute are not available.  A route is
   exportable to an AS if it is the least specific aggregate exportable
   to that AS or it is listed in the export-comps attribute of an
   exportable route.  Note that this is a recursive definition.

   route:        128.8.0.0/15
   origin:       AS1
   aggr-bndry:   AS1 or AS2
   aggr-mtd:     outbound
   inject:       upon HAVE-COMPONENTS {128.8.0.0/16, 128.9.0.0/16}

   route:        128.10.0.0/15
   origin:       AS1
   aggr-bndry:   AS1 or AS3
   aggr-mtd:     outbound
   inject:       upon HAVE-COMPONENTS {128.10.0.0/16, 128.11.0.0/16}
   export-comps: {128.11.0.0/16}

   route:        128.8.0.0/14
   origin:       AS1
   aggr-bndry:   AS1 or AS2 or AS3
   aggr-mtd:     outbound
   inject:       upon HAVE-COMPONENTS {128.8.0.0/15, 128.10.0.0/15}
   export-comps: {128.10.0.0/15}


                   Figure 34:  Overlapping aggregations.

   In Figure 34, AS1 together with AS2 aggregates 128.8.0.0/16 and
   128.9.0.0/16 into 128.8.0.0/15.  Together with AS3, AS1 aggregates
   128.10.0.0/16 and 128.11.0.0/16 into 128.10.0.0/15.  But altogether
   they aggregate these four routes into 128.8.0.0/14.  Assuming all
   four components are available, a router in AS1 for an outside AS, say
   AS4, will first generate 128.8.0.0/15 and 128.10.0.0/15.  This will
   make 128.8.0.0/15, 128.10.0.0/15 and its exception 128.11.0.0/16
   available for generating 128.8.0.0/14.  The router will then generate
   128.8.0.0/14 from these three routes.  Hence for AS4, 128.8.0.0/14
   and its exception 128.10.0.0/15 and its exception 128.11.0.0/16 will
   be exportable.

   For AS2, a router in AS1 will only generate 128.10.0.0/15.  Hence,
   128.10.0.0/15 and its exception 128.11.0.0/16 will be exportable.
   Note that 128.8.0.0/16 and 128.9.0.0/16 are also exportable since
   they did not participate in an aggregate exportable to AS2.

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   Similarly, for AS3, a router in AS1 will only generate 128.8.0.0/15.
   In this case 128.8.0.0/15, 128.10.0.0/16, 128.11.0.0/16 are
   exportable.

8.2 Specifying Static Routes

   The inject attribute can be used to specify static routes by using
   "upon static" as the condition:

  inject: [at <router-expression>] ...
          [action <action>]
          upon static

   In this case, the routers in <router-expression> executes the
   <action> and injects the route to the interAS routing system
   statically.  <action> may set certain route attributes such as a
   next-hop router or a cost.

   In the following example, the router 7.7.7.1 injects the route
   128.7.0.0/16.  The next-hop routers (in this example, there are two
   next-hop routers) for this route are 7.7.7.2 and 7.7.7.3 and the
   route has a cost of 10 over 7.7.7.2 and 20 over 7.7.7.3.

   route:  128.7.0.0/16
   origin: AS1
   inject: at 7.7.7.1 action next-hop = 7.7.7.2; cost = 10; upon static
   inject: at 7.7.7.1 action next-hop = 7.7.7.3; cost = 20; upon static



(page 52 continued on part 3)

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