Request for Comments: 2280 USC/Information Sciences Institute
Category: Standards Track T. Bates
Cisco Systems
E. Gerich
At Home Network
D. Karrenberg
RIPE
D. Meyer
University of Oregon
M. Terpstra
Bay Networks
C. Villamizar
ANS
January 1998
Routing Policy Specification Language (RPSL)
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Table of Contents
1 Introduction 2
2 RPSL Names, Reserved Words, and Representation 3
3 Contact Information 6
3.1 mntner Class . . . . . . . . . . . . . . . . . . . . . . . 6
3.2 person Class . . . . . . . . . . . . . . . . . . . . . . . 8
3.3 role Class . . . . . . . . . . . . . . . . . . . . . . . . 9
4 route Class 10
5 Set Classes 12
5.1 route-set Class . . . . . . . . . . . . . . . . . . . . . . 12
5.2 as-set Class . . . . . . . . . . . . . . . . . . . . . . . 14
5.3 Predefined Set Objects . . . . . . . . . . . . . . . . . . 15
5.4 Hierarchical Set Names . . . . . . . . . . . . . . . . . . 15
6 aut-num Class 16
6.1 import Attribute: Import Policy Specification . . . . . . 16
6.1.1 Peering Specification . . . . . . . . . . . . . . . . . 17
6.1.2 Action Specification . . . . . . . . . . . . . . . . . 19
6.1.3 Filter Specification . . . . . . . . . . . . . . . . . 20
6.1.4 Example Policy Expressions . . . . . . . . . . . . . . 24
6.2 export Attribute: Export Policy Specification . . . . . . 24
6.3 Other Routing Protocols, Multi-Protocol Routing
Protocols, and Injecting Routes Between Protocols . . . . . 25
6.4 Ambiguity Resolution . . . . . . . . . . . . . . . . . . . 26
6.5 default Attribute: Default Policy Specification . . . . . 28
6.6 Structured Policy Specification . . . . . . . . . . . . . . 29
7 dictionary Class 33
7.1 Initial RPSL Dictionary and Example Policy Actions
and Filters . . . . . . . . . . . . . . . . . . . . . . . . . 36
8 Advanced route Class 41
8.1 Specifying Aggregate Routes . . . . . . . . . . . . . . . . 41
8.1.1 Interaction with policies in aut-num class . . . . . . 45
8.1.2 Ambiguity resolution with overlapping aggregates . . . 46
8.2 Specifying Static Routes . . . . . . . . . . . . . . . . . 47
9 inet-rtr Class 48
10 Security Considerations 49
11 Acknowledgements 50
A Routing Registry Sites 51
B Authors' Addresses 52
C Full Copyright Statement 53
1 Introduction
This memo is the reference document for the Routing Policy
Specification Language (RPSL). RPSL allows a network operator to be
able to specify routing policies at various levels in the Internet
hierarchy; for example at the Autonomous System (AS) level. At the
same time, policies can be specified with sufficient detail in RPSL
so that low level router configurations can be generated from them.
RPSL is extensible; new routing protocols and new protocol features
can be introduced at any time.
RPSL is a replacement for the current Internet policy specification
language known as RIPE-181 [4] or RFC-1786 [5]. RIPE-81 [6] was the
first language deployed in the Internet for specifying routing
policies. It was later replaced by RIPE-181 [4]. Through
operational use of RIPE-181 it has become apparent that certain
policies cannot be specified and a need for an enhanced and more
generalized language is needed. RPSL addresses RIPE-181's
limitations.
RPSL was designed so that a view of the global routing policy can be
contained in a single cooperatively maintained distributed database
to improve the integrity of Internet's routing. RPSL is not designed
to be a router configuration language. RPSL is designed so that
router configurations can be generated from the description of the
policy for one autonomous system (aut-num class) combined with the
description of a router (inet-rtr class), mainly providing router ID,
autonomous system number of the router, interfaces and peers of the
router, and combined with a global database mappings from AS sets to
ASes (as-set class), and from origin ASes and route sets to route
prefixes (route and route-set classes). The accurate population of
the RPSL database can help contribute toward such goals as router
configurations that protect against accidental (or malicious)
distribution of inaccurate routing information, verification of
Internet's routing, and aggregation boundaries beyond a single AS.
RPSL is object oriented; that is, objects contain pieces of policy
and administrative information. These objects are registered in the
Internet Routing Registry (IRR) by the authorized organizations. The
registration process is beyond the scope of this document. Please
refer to [1, 15, 2] for more details on the IRR.
In the following sections, we present the classes that are used to
define various policy and administrative objects. The "mntner" class
defines entities authorized to add, delete and modify a set of
objects. The "person" and "role" classes describes technical and
administrative contact personnel. Autonomous systems (ASes) are
specified using the "aut-num" class. Routes are specified using the
"route" class. Sets of ASes and routes can be defined using the
"as-set" and "route-set" classes. The "dictionary" class provides
the extensibility to the language. The "inet-rtr" class is used to
specify routers. Many of these classes were originally defined in
earlier documents [4, 11, 14, 10, 3] and have all been enhanced.
This document is self-contained. However, the reader is encouraged
to read RIPE-181 [5] and the associated documents [11, 14, 10, 3] as
they provide significant background as to the motivation and
underlying principles behind RIPE-181 and consequently, RPSL. For a
tutorial on RPSL, the reader should read the RPSL applications
document [2].
2 RPSL Names, Reserved Words, and Representation
Each class has a set of attributes which store a piece of information
about the objects of the class. Attributes can be mandatory or
optional: A mandatory attribute has to be defined for all objects of
the class; optional attributes can be skipped. Attributes can also
be single or multiple valued. Each object is uniquely identified by
a set of attributes, referred to as the class "key".
The value of an attribute has a type. The following types are most
widely used. Note that RPSL is case insensitive and only the
characters from the ASCII character set can be used.
<object-name>Many objects in RPSL have a name. An <object-name>
is made up of letters, digits, the character underscore "_", and
the character hyphen "-"; the first character of a name must be a
letter, and the last character of a name must be a letter or a
digit. The following words are reserved by RPSL, and they can
not be used as names:
any as-any rs-any peeras
and or not
atomic from to at action accept announce except refine
networks into inbound outbound
Names starting with certain prefixes are reserved for certain
object types. Names starting with "as-" are reserved for as set
names. Names starting with "rs-" are reserved for route set
names.
<as-number>An AS number x is represented as the string "ASx". That
is, the AS 226 is represented as AS226.
<ipv4-address>An IPv4 address is represented as a sequence of four
integers in the range from 0 to 255 separated by the character
dot ".". For example, 128.9.128.5 represents a valid IPv4
address. In the rest of this document, we may refer to IPv4
addresses as IP addresses.
<address-prefix>An address prefix is represented as an IPv4
address followed by the character slash "/" followed by an
integer in the range from 0 to 32. The following are valid
address prefixes: 128.9.128.5/32, 128.9.0.0/16, 0.0.0.0/0; and
the following address prefixes are invalid: 0/0, 128.9/16 since 0
or 128.9 are not strings containing four integers.
<address-prefix-range>An address prefix range is an address
prefix followed by one of the following range operators:
^- is the exclusive more specifics operator; it stands
for the more specifics of the address prefix excluding the
address prefix itself. For example, 128.9.0.0/16^- contains
all the more specifics of 128.9.0.0/16 excluding
128.9.0.0/16.
^+ is the inclusive more specifics operator; it stands
for the more specifics of the address prefix including the
address prefix itself. For example, 5.0.0.0/8^+ contains all
the more specifics of 5.0.0.0/8 including 5.0.0.0/8.
^n where n is an integer, stands for all the length n specifics
of the address prefix. For example, 30.0.0.0/8^16 contains
all the more specifics of 30.0.0.0/8 which are of length 16
such as 30.9.0.0/16.
^n-m where n and m are integers, stands for all the length n to
length m specifics of the address prefix. For example,
30.0.0.0/8^24-32 contains all the more specifics of
30.0.0.0/8 which are of length 24 to 32 such as 30.9.9.96/28.
Range operators can also be applied to address prefix sets. In
this case, they distribute over the members of the set. For
example, for a route-set (defined later) rs-foo, rs-foo^+
contains all the inclusive more specifics of all the prefixes in
rs-foo.
<date>A date is represented as an eight digit integer of the
form YYYYMMDD where YYYY represents the year, MM represents the
month of the year (01 through 12), and DD represents the day of
the month (01 through 31). For example, June 24, 1996 is
represented as 19960624.
<email-address>is as described in RFC-822[8].
<dns-name>is as described in RFC-1034[16].
<nic-handle>is a uniquely assigned identifier[13] used by routing,
address allocation, and other registries to unambiguously refer
to contact information. person and role classes map NIC handles
to actual person names, and contact information.
<free-form>is a sequence of ASCII characters.
<X-name>is a name of an object of type X. That is <mntner-name>
is a name of a mntner object.
<registry-name>is a name of an IRR registry. The routing
registries are listed in Appendix A.
A value of an attribute may also be a list of one of these types. A
list is represented by separating the list members by commas ",".
For example, "AS1, AS2, AS3, AS4" is a list of AS numbers. Note that
being list valued and being multiple valued are orthogonal. A
multiple valued attribute has more than one value, each of which may
or may not be a list. On the other hand a single valued attribute
may have a list value.
An RPSL object is textually represented as a list of attribute-value
pairs. Each attribute-value pair is written on a separate line. The
attribute name starts at column 0, followed by character ":" and
followed by the value of the attribute. The object's representation
ends when a blank line is encountered. An attribute's value can be
split over multiple lines, by starting the continuation lines with a
white-space (" " or tab) character. The order of attribute-value
pairs is significant.
An object's description may contain comments. A comment can be
anywhere in an object's definition, it starts at the first "#"
character on a line and ends at the first end-of-line character.
White space characters can be used to improve readability.
3 Contact Information
The mntner, person and role classes, admin-c, tech-c, mnt-by,
changed, and source attributes of all classes describe contact
information. The mntner class also specifies what entities can
create, delete and update other objects. These classes do not
specify routing policies and each registry may have different or
additional requirements on them. Here we present the common
denominator for completeness which is the RIPE database
implementation[15]. Please consult your routing registry for the
latest specification of these classes and attributes.
3.1 mntner Class
The mntner class defines entities that can create, delete and update
RPSL objects. A provider, before he/she can create RPSL objects,
first needs to create a mntner object. The attributes of the mntner
class are shown in Figure 1. The mntner class was first described in
[11].
The mntner attribute is mandatory and is the class key attribute.
Its value is an RPSL name. The auth attribute specifies the scheme
that will be used
Attribute Value Type
mntner <object-name> mandatory, single-valued, class key
descr <free-form> mandatory, single-valued
auth see description in text mandatory, multi-valued
upd-to <email-address> mandatory, multi-valued
mnt-nfy <email-address> optional, multi-valued
tech-c <nic-handle> mandatory, multi-valued
admin-c <nic-handle> mandatory, multi-valued
remarks <free-form> optional, multi-valued
notify <email-address> optional, multi-valued
mnt-by list of <mntner-name> mandatory, multi-valued
changed <email-address> <date> mandatory, multi-valued
source <registry-name> mandatory, single-valued
to identify and authenticate update requests from this maintainer.
It has the following syntax:
auth: <scheme-id> <auth-info>
E.g.
auth: NONE
auth: CRYPT-PW dhjsdfhruewf
auth: MAIL-FROM .*@ripe\.net
The <scheme-id>'s currently defined are: NONE, MAIL-FROM, PGP and
CRYPT-PW. The <auth-info> is additional information required by a
particular scheme: in the case of MAIL-FROM, it is a regular
expression matching valid email addresses; in the case of CRYPT-PW,
it is a password in UNIX crypt format; and in the case of PGP, it is
a PGP public key. If multiple auth attributes are specified, an
update request satisfying any one of them is authenticated to be from
the maintainer.
The upd-to attribute is an email address. On an unauthorized update
attempt of an object maintained by this maintainer, an email message
will be sent to this address. The mnt-nfy attribute is an email
address. A notification message will be forwarded to this email
address whenever an object maintained by this maintainer is added,
changed or deleted.
The descr attribute is a short, free-form textual description of the
object. The tech-c attribute is a technical contact NIC handle.
This is someone to be contacted for technical problems such as
misconfiguration. The admin-c attribute is an administrative contact
NIC handle. The remarks attribute is a free text explanation or
clarification. The notify attribute is an email address to which
notifications of changes to this object should be sent. The mnt-by
attribute is a list of mntner object names. The authorization for
changes to this object is governed by any of the maintainer objects
referenced. The changed attribute documents who last changed this
object, and when this change was made. Its syntax has the following
form:
changed: <email-address> <YYYYMMDD>
E.g.
changed: johndoe@terabit-labs.nn 19900401
The <email-address> identifies the person who made the last change.
<YYYYMMDD> is the date of the change. The source attribute specifies
the registry where the object is registered. Figure 2 shows an
example mntner object. In the example, UNIX crypt format password
authentication is used.
mntner: RIPE-NCC-MNT
descr: RIPE-NCC Maintainer
admin-c: DK58
tech-c: OPS4-RIPE
upd-to: ops@ripe.net
mnt-nfy: ops-fyi@ripe.net
auth: CRYPT-PW lz1A7/JnfkTtI
mnt-by: RIPE-NCC-MNT
changed: ripe-dbm@ripe.net 19970820
source: RIPE
Figure 2: An example mntner object.
The descr, tech-c, admin-c, remarks, notify, mnt-by, changed and
source attributes are attributes of all RPSL classes. Their syntax,
semantics, and mandatory, optional, multi-valued, or single-valued
status are the same for for all RPSL classes. We do not further
discuss them in other sections.
3.2 person Class
A person class is used to describe information about people. Even
though it does not describe routing policy, we still describe it here
briefly since many policy objects make reference to person objects.
The person class was first described in [14].
The attributes of the person class are shown in Figure 3. The person
attribute is the full name of the person. The phone and the fax-no
attributes have the following syntax:
Attribute Value Type
person <free-form> mandatory, single-valued
nic-hdl <nic-handle> mandatory, single-valued, class key
address <free-form> mandatory, multi-valued
phone see description in text mandatory, multi-valued
fax-no same as phone optional, multi-valued
e-mail <email-address> mandatory, multi-valued
Figure 3: person Class Attributes
phone: +<country-code> <city> <subscriber> [ext. <extension>]
E.g.:
phone: +31 20 12334676
phone: +44 123 987654 ext. 4711
Figure 4 shows an example person object.
person: Daniel Karrenberg
address: RIPE Network Coordination Centre (NCC)
address: Singel 258
address: NL-1016 AB Amsterdam
address: Netherlands
phone: +31 20 535 4444
fax-no: +31 20 535 4445
e-mail: Daniel.Karrenberg@ripe.net
nic-hdl: DK58
changed: Daniel.Karrenberg@ripe.net 19970616
source: RIPE
Figure 4: An example person object.
3.3 role Class
The role class is similar to the person object. However, instead of
describing a human being, it describes a role performed by one or
more human beings. Examples include help desks, network monitoring
centers, system administrators, etc. Role object is particularly
useful since often a person performing a role may change, however the
role itself remains.
The attributes of the role class are shown in Figure 5. The nic-hdl
attributes of the person and role classes share the same name space.
The
Attribute Value Type
role <free-form> mandatory, single-valued
nic-hdl <nic-handle> mandatory, single-valued, class key
trouble <free-form> optional, multi-valued
address <free-form> mandatory, multi-valued
phone see description in text mandatory, multi-valued
fax-no same as phone optional, multi-valued
e-mail <email-address> mandatory, multi-valued
Figure 5: role Class Attributes
NIC handle of a role object cannot be used in an admin-c field. The
trouble attribute of role object may contain additional contact
information to be used when a problem arises in any object that
references this role object. Figure 6 shows an example role object.
role: RIPE NCC Operations
address: Singel 258
address: 1016 AB Amsterdam
address: The Netherlands
phone: +31 20 535 4444
fax-no: +31 20 545 4445
e-mail: ops@ripe.net
admin-c: CO19-RIPE
tech-c: RW488-RIPE
tech-c: JLSD1-RIPE
nic-hdl: OPS4-RIPE
notify: ops@ripe.net
changed: roderik@ripe.net 19970926
source: RIPE
Figure 6: An example role object.
4 route Class
Each interAS route (also referred to as an interdomain route)
originated by an AS is specified using a route object. The
attributes of the route class are shown in Figure 7. The route
attribute is the address prefix of the route and the origin attribute
is the AS number of the AS that originates the route into the interAS
routing system. The route and origin attribute pair is the class
key.
Figure 8 shows examples of four route objects (we do not include
contact.
Attribute Value Type
route <address-prefix> mandatory, single-valued,
class key
origin <as-number> mandatory, single-valued,
class key
withdrawn <date> optional, single-valued
member-of list of <route-set-names> optional, single-valued
see Section 5
inject see Section 8 optional, multi-valued
components see Section 8 optional, single-valued
aggr-bndry see Section 8 optional, single-valued
aggr-mtd see Section 8 optional, single-valued
export-comps see Section 8 optional, single-valued
holes see Section 8 optional, single-valued
Figure 7: route Class Attributes
attributes such as admin-c, tech-c for brevity). Note that the last
two route objects have the same address prefix, namely 128.8.0.0/16.
However, they are different route objects since they are originated
by different ASes (i.e. they have different keys).
route: 128.9.0.0/16
origin: AS226
route: 128.99.0.0/16
origin: AS226
route: 128.8.0.0/16
origin: AS1
route: 128.8.0.0/16
origin: AS2
withdrawn: 19960624
Figure 8: Route Objects
The withdrawn attribute, if present, signifies that the originator AS
no longer originates this address prefix in the Internet. Its value
is a date indicating the date of withdrawal. In Figure 8, the last
route object is withdrawn (i.e. no longer originated by AS2) on June
24, 1996.
5 Set Classes
To specify policies, it is often useful to define sets of objects.
For this purpose we define two classes: route-set and as-set. These
classes define a named set. The members of these sets can be
specified by either explicitly listing them in the set object's
definition, or implicitly by having route and aut-num objects refer
to the set names, or a combination of both methods.
5.1 route-set Class
The attributes of the route-set class are shown in Figure 9. The
route-set attribute defines the name of the set. It is an RPSL name
that starts with "rs-". The members attribute lists the members of
the set. The members attribute is a list of address prefixes or
other route-set names. Note that, the route-set class is a set of
route prefixes, not of RPSL route objects.
Attribute Value Type
route-set <object-name> mandatory, single-valued,
class key
members list of <address-prefixes> or optional, single-valued
<route-set-names>
mbrs-by-ref list of <mntner-names> optional, single-valued
Figure 9: route-set Class Attributes
Figure 10 presents some example route-set objects. The set rs-foo
contains two address prefixes, namely 128.9.0.0/16 and 128.9.0.0/16.
The set rs-bar contains the members of the set rs-foo and the address
prefix 128.7.0.0/16. The set rs-empty contains no members.
route-set: rs-foo
members: 128.9.0.0/16, 128.9.0.0/24
route-set: rs-bar
members: 128.7.0.0/16, rs-foo
route-set: rs-empty
Figure 10: route-set Objects
An address prefix or a route-set name in a members attribute can be
optionally followed by a range operator. For example, the following
set
route-set: rs-bar
members: 5.0.0.0/8^+, 30.0.0.0/8^24-32, rs-foo^+
contains all the more specifics of 5.0.0.0/8 including 5.0.0.0/8, all
the more specifics of 30.0.0.0/8 which are of length 24 to 32 such as
30.9.9.96/28, and all the more specifics of address prefixes in route
set rs-foo.
The mbrs-by-ref attribute is a list of maintainer names or the
keyword ANY. If this attribute is used, the route set also includes
address prefixes whose route objects are registered by one of these
maintainers and whose member-of attribute refers to the name of this
route set. If the value of a mbrs-by-ref attribute is ANY, any route
object referring to the route set name is a member. If the mbrs-by-
ref attribute is missing, only the address prefixes listed in the
members attribute are members of the set.
route-set: rs-foo
mbrs-by-ref: MNTR-ME, MNTR-YOU
route-set: rs-bar
members: 128.7.0.0/16
mbrs-by-ref: MNTR-YOU
route: 128.9.0.0/16
origin: AS1
member-of: rs-foo
mnt-by: MNTR-ME
route: 128.8.0.0/16
origin: AS2
member-of: rs-foo, rs-bar
mnt-by: MNTR-YOU
Figure 11: route-set objects.
Figure 11 presents example route-set objects that use the mbrs-by-ref
attribute. The set rs-foo contains two address prefixes, namely
128.8.0.0/16 and 128.9.0.0/16 since the route objects for
128.8.0.0/16 and 128.9.0.0/16 refer to the set name rs-foo in their
member-of attribute. The set rs-bar contains the address prefixes
128.7.0.0/16 and 128.8.0.0/16. The route 128.7.0.0/16 is explicitly
listed in the members attribute of rs-bar, and the route object for
128.8.0.0/16 refer to the set name rs-bar in its member-of attribute.
Note that, if an address prefix is listed in a members attribute of a
route set, it is a member of that route set. The route object
corresponding to this address prefix does not need to contain a
member-of attribute referring to this set name. The member-of
attribute of the route class is an additional mechanism for
specifying the members indirectly.
5.2 as-set Class
The attributes of the as-set class are shown in Figure 12. The as-
set attribute defines the name of the set. It is an RPSL name that
starts with "as-". The members attribute lists the members of the
set. The members attribute is a list of AS numbers, or other as-set
names.
Attribute Value Type
as-set <object-name> mandatory, single-valued,
class key
members list of <as-numbers> or optional, single-valued
<as-set-names>
mbrs-by-ref list of <mntner-names> optional, single-valued
Figure 12: as-set Class Attributes
Figure 13 presents two as-set objects. The set as-foo contains two
ASes, namely AS1 and AS2. The set as-bar contains the members of the
set as-foo and AS3, that is it contains AS1, AS2, AS3.
as-set: as-foo as-set: as-bar
members: AS1, AS2 members: AS3, as-foo
Figure 13: as-set objects.
The mbrs-by-ref attribute is a list of maintainer names or the
keyword ANY. If this attribute is used, the AS set also includes
ASes whose aut-num objects are registered by one of these maintainers
and whose member-of attribute refers to the name of this AS set. If
the value of a mbrs-by-ref attribute is ANY, any AS object referring
to the AS set is a member of the set. If the mbrs-by-ref attribute
is missing, only the ASes listed in the members attribute are members
of the set.
Figure 14 presents an example as-set object that uses the mbrs-by-ref
attribute. The set as-foo contains AS1, AS2 and AS3. AS4 is not a
member of the set as-foo even though the aut-num object references
as-foo. This is because MNTR-OTHER is not listed in the as-foo's
mbrs-by-ref attribute.
as-set: as-foo
members: AS1, AS2
mbrs-by-ref: MNTR-ME
aut-num: AS3 aut-num: AS4
member-of: as-foo member-of: as-foo
mnt-by: MNTR-ME mnt-by: MNTR-OTHER
Figure 14: as-set objects.
5.3 Predefined Set Objects
In a context that expects a route set (e.g. members attribute of the
route-set class), an AS number ASx defines the set of routes that are
originated by ASx; and an as-set AS-X defines the set of routes that
are originated by the ASes in AS-X. A route p is said to be
originated by ASx if there is a route object for p with ASx as the
value of the origin attribute. For example, in Figure 15, the route
set rs-special contains 128.9.0.0/16, routes of AS1 and AS2, and
routes of the ASes in AS set AS-FOO.
route-set: rs-special
members: 128.9.0.0/16, AS1, AS2, AS-FOO
Figure 15: Use of AS numbers and AS sets in route sets.
The set rs-any contains all routes registered in IRR. The set as-any
contains all ASes registered in IRR.
5.4 Hierarchical Set Names
Set names can be hierarchical. A hierarchical set name is a sequence
of set names and AS numbers separated by colons ":". For example,
the following names are valid: AS1:AS-CUSTOMERS, AS1:RS-EXCEPTIONS,
AS1:RS-EXPORT:AS2, RS-EXCEPTIONS:RS-BOGUS. All components of an
hierarchical set name which are not AS numbers should start with
"as-" or "rs-" for as sets and route sets respectively.
A set object with name X1:...:Xn-1:Xn can only be created by the
maintainer of the object with name X1:...:Xn-1. That is, only the
maintainer of AS1 can create a set with name AS1:AS-FOO; and only the
maintainer of AS1:AS-FOO can create a set with name AS1:AS-FOO:AS-
BAR.
The purpose of an hierarchical set name is to partition the set name
space so that the controllers of the set name X1 controls the whole
set name space under X1, i.e. X1:...:Xn-1. This is important since
anyone can create a set named AS-MCI-CUSTOMERS but only the people
created AS3561 can create AS3561:AS-CUSTOMERS. In the former, it is
not clear if the set AS-MCI-CUSTOMERS has any relationship with MCI.
In the latter, we can guarantee that AS3561:AS-CUSTOMERS and AS3561
are created by the same entity.
6 aut-num Class
ASes are specified using the aut-num class. The attributes of the
aut-num class are shown in Figure 16. 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, single-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 16: aut-num Class Attributes
6.1 import Attribute: Import Policy Specification
Figure 17 shows a typical interconnection of ASes that we will be
using in our examples throughout this section. In this example
topology, there are three ASes, AS1, AS2, and AS3; two exchange
points, EX1 and EX2; and six routers. Routers connected to the same
exchange point peer with each other, i.e. open a connection for
exchanging routing information. Each router would export a subset of
the routes it has to its peer routers. Peer routers would import a
subset of these routes. A router while importing routes would set
some route attributes. For example, AS1 can assign higher preference
values to the routes it imports from AS2 so that it prefers AS2 over
AS3. While exporting routes, a router may also set some route
attributes in order to affect route selection by its peers. For
example, AS2 may set the MULTI-EXIT-DISCRIMINATOR BGP attribute so
that AS1 prefers to use the router 9.9.9.2. Most interAS policies
are specified by specifying what route subsets can be imported or
exported, and how the various BGP route attributes are set and used.
---------------------- ----------------------
| 7.7.7.1 |-------| |-------| 7.7.7.2 |
| | ======== | |
| AS1 | EX1 |-------| 7.7.7.3 AS2 |
| | | |
| 9.9.9.1 |------ ------| 9.9.9.2 |
---------------------- | | ----------------------
===========
| EX2
---------------------- |
| 9.9.9.3 |---------
| |
| AS3 |
----------------------
Figure 17: Example topology consisting of three ASes, AS1, AS2, and
AS3; two exchange points, EX1 and EX2; and six routers.
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. In the next few subsections, we will describe how
peerings, actions and filters are specified.
6.1.1 Peering Specification
Our example above used an AS number to specify peerings. The
peerings can be specified at different granularities. The syntax of
a peering specification has two forms. The first one is as follows:
<peer-as> [<peer-router>] [at <local-router>]
where <local-router> and <peer-router> are IP addresses of routers,
<peer-as> is an AS number. <peer-as> must be the AS number of
<peer-router>. Both <local-router> and <peer-router> are optional.
If both <local-router> and <peer-router> are specified, this peering
specification identifies only the peering between these two routers.
If only <local-router> is specified, this peering specification
identifies all the peerings between <local-router> and any of its
peer routers in <peer-as>. If only <peer-router> is specified, this
peering specification identifies all the peerings between any router
in the local AS and <peer-router>. If neither <local-router> nor
<peer-router> is specified, this peering specification identifies all
the peerings between any router in the local AS and any router in
<peer-as>.
We next give examples. Consider the topology of Figure 17 where
7.7.7.1, 7.7.7.2 and 7.7.7.3 peer with each other; 9.9.9.1, 9.9.9.2
and 9.9.9.3 peer with each other. In the following example 7.7.7.1
imports 128.9.0.0/16 from 7.7.7.2.
(1) aut-num: AS1
import: from AS2 7.7.7.2 at 7.7.7.1 accept { 128.9.0.0/16 }
In the following example 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2
and 7.7.7.3.
(2) aut-num: AS1
import: from AS2 at 7.7.7.1 accept { 128.9.0.0/16 }
In the following example 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2
and 7.7.7.3, and 9.9.9.1 imports 128.9.0.0/16 from 9.9.9.2.
(3) aut-num: AS1
import: from AS2 accept { 128.9.0.0/16 }
The second form of <peering> specification has the following syntax:
<as-expression> [at <router-expression>]
where <as-expression> is an expression over AS numbers and sets using
operators AND, OR, and NOT, and <router-expression> is an expression
over router IP addresses and DNS names using operators AND, OR, and
NOT. The DNS name can only be used if there is an inet-rtr object for
that name that binds the name to IP addresses. This form identifies
all the peerings between any local router in <router-expression> to
any of their peer routers in the ASes in <as-expression>. If
<router-expression> is not specified, it defaults to all routers of
the local AS.
In the following example 9.9.9.1 imports 128.9.0.0/16 from 9.9.9.2
and 9.9.9.3.
(4) as-set: AS-FOO
members: AS2, AS3
aut-num: AS1
import: from AS-FOO at 9.9.9.1 accept { 128.9.0.0/16 }
In the following example 9.9.9.1 imports 128.9.0.0/16 from 9.9.9.2
and 9.9.9.3, and 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2 and
7.7.7.3.
(5) aut-num: AS1
import: from AS-FOO accept { 128.9.0.0/16 }
In the following example AS1 imports 128.9.0.0/16 from AS3 at router
9.9.9.1
(6) aut-num: AS1
import: from AS-FOO and not AS2
at not 7.7.7.1
accept { 128.9.0.0/16 }
This is because "AS-FOO and not AS2" equals AS3 and "not 7.7.7.1"
equals 9.9.9.1.
6.1.2 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 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 community path attribute.
6.1.3 Filter Specification
A policy filter is a logical expression which when applied to a set
of routes returns a subset of these routes. We say that the policy
filter matches the subset returned. The policy filter can match
routes using any path attribute, such as the destination address
prefix (or NLRI), AS-path, or community attributes.
The policy filters can be composite by using the operators AND, OR,
and NOT. The following policy filters can be used to select a subset
of routes:
ANY The filter-keyword ANY matches all routes.
Address-Prefix Set This is an explicit list of address prefixes
enclosed in braces '{' and '}'. The policy filter matches the set of
routes whose destination address-prefix is in the set. For example:
{ 0.0.0.0/0 }
{ 128.9.0.0/16, 128.8.0.0/16, 128.7.128.0/17, 5.0.0.0/8 }
{ }
An address prefix can be optionally followed by a range operator
(i.e. '^-', '^+', '^n', or '^n-m'). For example, the set
{ 5.0.0.0/8^+, 128.9.0.0/16^-, 30.0.0.0/8^16, 30.0.0.0/8^24-32 }
contains all the more specifics of 5.0.0.0/8 including 5.0.0.0/8, all
the more specifics of 128.9.0.0/16 excluding 128.9.0.0/16, all the
more specifics of 30.0.0.0/8 which are of length 16 such as
30.9.0.0/16, and all the more specifics of 30.0.0.0/8 which are of
length 24 to 32 such as 30.9.9.96/28.
Route Set Name A route set name matches the set of routes that are
members of the set. A route set name may be a name of a route-set
object, an AS number, or a name of an as-set object (AS numbers and
as-set names implicitly define route sets; please see Section 5.3).
For example:
aut-num: AS1
import: from AS2 action pref = 1; accept AS2
import: from AS2 action pref = 1; accept AS-FOO
import: from AS2 action pref = 1; accept RS-FOO
The keyword PeerAS can be used instead of the AS number of the peer
AS. PeerAS is particularly useful when the peering is specified
using an AS expression. For example:
as-set: AS-FOO
members: AS2, AS3
aut-num: AS1
import: from AS-FOO action pref = 1; accept PeerAS
is same as:
aut-num: AS1
import: from AS2 action pref = 1; accept AS2
import: from AS3 action pref = 1; accept AS3
A route set name can also be followed by one of the operators '^-',
'^+', '^n' or '^n-m'. These operators are distributive over the
route sets. For example, { 5.0.0.0/8, 6.0.0.0/8 }^+ equals {
5.0.0.0/8^+, 6.0.0.0/8^+ }, and AS1^- equals all the exclusive more
specifics of routes originated by AS1.
AS Path Regular Expressions An AS-path regular expression can be used
as a policy filter by enclosing the expression in `<' and `>'. An
AS-path policy filter matches the set of routes which traverses a
sequence of ASes matched by the AS-path regular expression. A router
can check this using the AS_PATH attribute in the Border Gateway
Protocol [18], or the RD_PATH attribute in the Inter-Domain Routing
Protocol[17].
AS-path Regular Expressions are POSIX compliant regular expressions
over the alphabet of AS numbers. The regular expression constructs
are as follows:
ASN where ASN is an AS number. ASN matches the AS-path
that is of length 1 and contains the corresponding AS
number (e.g. AS-path regular expression AS1 matches the
AS-path "1").
The keyword PeerAS can be used instead of the AS number
of the peer AS.
AS-set where AS-set is an AS set name. AS-set matches the AS-paths
that is matched by one of the ASes in the AS-set.
. matches the AS-paths matched by any AS number.
[...] is an AS number set. It matches the AS-paths matched by
the AS numbers listed between the brackets. The AS
numbers in the set are separated by white space
characters. If a `-' is used between two AS numbers in
this set, all AS numbers between the two AS numbers are
included in the set. If an as-set name is listed, all
AS numbers in the as-set are included.
[^...] is a complemented AS number set. It matches any AS-path
which is not matched by the AS numbers in the set.
^ Matches the empty string at the beginning of an AS-path.
$ Matches the empty string at the end of an AS-path.
We next list the regular expression operators in the decreasing order
of evaluation. These operators are left associative, i.e. performed
left to right.
Unary postfix operators * + ? {m} {m,n} {m,}
For a regular expression A, A* matches zero or more
occurrences of A; A+ matches one or more occurrences of
A; A? matches zero or one occurrence of A; A{m} matches
m occurrence of A; A{m,n} matches m to n occurrence of
A; A{m,} matches m or more occurrence of A. For example,
[AS1 AS2]{2} matches AS1 AS1, AS1 AS2, AS2 AS1, and AS2
AS2.
Unary postfix operators ~* ~+ ~{m} ~{m,n} ~{m,}
These operators have similar functionality as the
corresponding operators listed above, but all
occurrences of the regular expression has to match the
same pattern. For example, [AS1 AS2]~{2} matches AS1
AS1 and AS2 AS2, but it does not match AS1 AS2 and AS2
AS1.
Binary catenation operator
This is an implicit operator and exists between two
regular expressions A and B when no other explicit
operator is specified. The resulting expression A B
matches an AS-path if A matches some prefix of the AS-
path and B matches the rest of the AS-path.
Binary alternative (or) operator |
For a regular expressions A and B, A | B matches any
AS-path that is matched by A or B.
Parenthesis can be used to override the default order of evaluation.
White spaces can be used to increase readability.
The following are examples of AS-path filters:
<AS3>
<^AS1>
<AS2$>
<^AS1 AS2 AS3$>
<^AS1 .* AS2$>.
The first example matches any route whose AS-path contains AS3, the
second matches routes whose AS-path starts with AS1, the third
matches routes whose AS-path ends with AS2, the fourth matches routes
whose AS-path is exactly "1 2 3", and the fifth matches routes whose
AS-path starts with AS1 and ends in AS2 with any number of AS numbers
in between.
Composite Policy Filters The following operators (in decreasing order
of evaluation) can be used to form composite policy filters:
NOT Given a policy filter x, NOT x matches the set of routes that are
not matched by x. That is it is the negation of policy filter x.
AND Given two policy filters x and y, x AND y matches the
intersection of the routes that are matched by x and that are
matched by y.
OR Given two policy filters x and y, x OR y matches the union of
the routes that are matched by x and that are matched by y.
Note that an OR operator can be implicit, that is `x y' is equivalent
to `x OR y'.
E.g.
NOT {128.9.0.0/16, 128.8.0.0/16}
AS226 AS227 OR AS228
AS226 AND NOT {128.9.0.0/16}
AS226 AND {0.0.0.0/0^0-18}
The first example matches any route except 128.9.0.0/16 and
128.8.0.0/16. The second example matches the routes of AS226, AS227
and AS228. The third example matches the routes of AS226 except
128.9.0.0/16. The fourth example matches the routes of AS226 whose
length are not longer than 18.
Routing Policy Attributes Policy filters can also use the values of
other attributes for comparison. The attributes whose values can be
used in policy filters are specified in the RPSL dictionary. Please
refer to Section 7 for details. An example using the the BGP
community attribute is shown below:
aut-num: AS1
export: to AS2 announce AS1 AND NOT community.contains(NO_EXPORT)
Filters using the routing policy attributes defined in the dictionary
are evaluated before evaluating the operators AND, OR and NOT.
6.1.4 Example Policy Expressions
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.
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>
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