Subcode is defined, then a zero (Unspecific) value is used for the
Error Subcode field.
Message Header Error Subcodes:
1 - Bad Message Length.
2 - Bad Message Type.
OPEN Message Error Subcodes:
1 - Unsupported Version Number.
2 - Bad Peer ITAD.
3 - Bad TRIP Identifier.
4 - Unsupported Optional Parameter.
5 - Unacceptable Hold Time.
6 - Unsupported Capability.
7 - Capability Mismatch.
UPDATE Message Error Subcodes:
1 - Malformed Attribute List.
2 - Unrecognized Well-known Attribute.
3 - Missing Well-known Mandatory Attribute.
4 - Attribute Flags Error.
5 - Attribute Length Error.
6 - Invalid Attribute.
Data:
This variable-length field is used to diagnose the reason for the
NOTIFICATION. The contents of the Data field depend upon the Error
Code and Error Subcode.
Note that the length of the data can be determined from the message
length field by the formula:
Data Length = Message Length - 5
The minimum length of the NOTIFICATION message is 5 octets (including
message header).
5. TRIP Attributes
This section provides details on the syntax and semantics of each
TRIP UPDATE attribute.
5.1. WithdrawnRoutes
Conditional Mandatory: False.
Required Flags: Well-known.
Potential Flags: Link-State Encapsulation (when flooding).
TRIP Type Code: 1
The WithdrawnRoutes specifies a set of routes that are to be removed
from service by the receiving LS(s). The set of routes MAY be empty,
indicated by a length field of zero.
5.1.1. Syntax of WithdrawnRoutes
The WithdrawnRoutes Attribute encodes a sequence of routes in its
value field. The format for individual routes is given in Section
5.1.1.1. The WithdrawnRoutes Attribute lists the individual routes
sequentially with no padding as shown in Figure 11. Each route
includes a length field so that the individual routes within the
attribute can be delineated.
+---------------------+---------------------+...
| WithdrawnRoute1... | WithdrawnRoute2... |...
+---------------------+---------------------+...
Figure 11: WithdrawnRoutes Format
5.1.1.1. Generic TRIP Route Format
The generic format for a TRIP route is given in Figure 12.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Address Family | Application Protocol |
+---------------+---------------+--------------+----------------+
| Length | Address (variable) ...
+---------------+---------------+--------------+----------------+
Figure 12: Generic TRIP Route Format
Address Family:
The address family field gives the type of address for the route.
Three address families are defined in this Section:
Code Address Family
1 Decimal Routing Numbers
2 PentaDecimal Routing Numbers
3 E.164 Numbers
This document reserves address family code 0. This document reserves
address family codes 32768-65535 for vendor-specific applications
(these are the codes with the first bit of the code value equal to
1). Additional address families may be defined in the future.
Assignment of address family codes is controlled by IANA. See
Section 13 for IANA considerations.
Application Protocol:
The application protocol gives the protocol for which this routing
table is maintained. The currently defined application protocols
are:
Code Protocol
1 SIP
2 H.323-H.225.0-Q.931
3 H.323-H.225.0-RAS
4 H.323-H.225.0-Annex-G
This document reserves application protocol code 0. This document
reserves application protocol codes 32768-65535 for vendor-specific
applications (these are the codes with the first bit of the code
value equal to 1). Additional application protocols may be defined
in the future. Assignment of application protocol codes is
controlled by IANA. See Section 13 for IANA considerations.
Length:
The length of the address field, in bytes.
Address:
This is an address (prefix) of the family type given by Address
Family. The octet length of the address is variable and is
determined by the length field of the route.
5.1.1.2. Decimal Routing Numbers
The Decimal Routing Numbers address family is a super set of all
E.164 numbers, national numbers, local numbers, and private numbers.
It can also be used to represent the decimal routing numbers used in
conjunction with Number Portability in some countries/regions. A set
of telephone numbers is specified by a Decimal Routing Number prefix.
Decimal Routing Number prefixes are represented by a string of
digits, each digit encoded by its ASCII character representation.
This routing object covers all phone numbers starting with this
prefix. The syntax for the Decimal Routing Number prefix is:
Decimal-routing-number = *decimal-digit
decimal-digit = DECIMAL-DIGIT
DECIMAL-DIGIT = "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9"
This DECIMAL Routing Number prefix is not bound in length. This
format is similar to the format for a global telephone number as
defined in SIP [8] without visual separators and without the "+"
prefix for international numbers. This format facilitates efficient
comparison when using TRIP to route SIP or H323, both of which use
character based representations of phone numbers. The prefix length
is determined from the length field of the route. The type of
Decimal Routing Number (private, local, national, or international)
can be deduced from the first few digits of the prefix.
5.1.1.3. PentaDecimal Routing Numbers
This address family is used to represent PentaDecimal Routing Numbers
used in conjunction with Number Portability in some
countries/regions. PentaDecimal Routing Number prefixes are
represented by a string of digits, each digit encoded by its ASCII
character representation. This routing object covers all routing
numbers starting with this prefix. The syntax for the PentaDecimal
Routing Number prefix is:
PentaDecimal-routing-number = *pentadecimal-digit
pentadecimal-routing-digit = PENTADECIMAL-DIGIT
PENTADECIMAL-DIGIT = "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|
"8"|"9"|"A"|"B"|"C"|"D"|"E"
Note the difference in alphabets between Decimal Routing Numbers and
PentaDecimal Routing Numbers. A PentaDecimal Routing Number prefix
is not bound in length.
Note that the address family, which suits the routing numbers of a
specific country/region depends on the alphabets used for routing
numbers in that country/region. For example, North American routing
numbers SHOULD use the Decimal Routing Numbers address family,
because their alphabet is limited to the digits "0" through "9".
Another example, in most European countries routing numbers use the
alphabet "0" through "9" and "A" through "E", and hence these
countries SHOULD use the PentaDecimal Routing Numbers address family.
5.1.1.4. E.164 Numbers
The E.164 Numbers address family is dedicated to fully qualified
E.164 numbers. A set of telephone numbers is specified by a E.164
prefix. E.164 prefixes are represented by a string of digits, each
digit encoded by its ASCII character representation. This routing
object covers all phone numbers starting with this prefix. The
syntax for the E.164 prefix is:
E164-number = *e164-digit
E164-digit = E164-DIGIT
E164-DIGIT = "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9"
This format facilitates efficient comparison when using TRIP to route
SIP or H323, both of which use character based representations of
phone numbers. The prefix length is determined from the length field
of the route.
The E.164 Numbers address family and the Decimal Routing Numbers
address family have the same alphabet. The E.164 Numbers address
family SHOULD be used whenever possible. The Decimal Routing Numbers
address family can be used in case of private numbering plans or
applications that do not desire to advertise fully expanded, fully
qualified telephone numbers. If Decimal Routing Numbers are used to
advertise non-fully qualified prefixes, the prefixes may have to be
manipulated (e.g. expanded) at the boundary between ITADs. This adds
significant complexity to the ITAD-Border LS, because, it has to map
the prefixes from the format used in its own ITAD to the format used
in the peer ITAD.
5.2. ReachableRoutes
Conditional Mandatory: False.
Required Flags: Well-known.
Potential Flags: Link-State Encapsulation (when flooding).
TRIP Type Code: 2
The ReachableRoutes attribute specifies a set of routes that are to
be added to service by the receiving LS(s). The set of routes MAY be
empty, as indicated by setting the length field to zero.
5.2.1. Syntax of ReachableRoutes
The ReachableRoutes Attribute has the same syntax as the
WithdrawnRoutes Attribute. See Section 5.1.1.
5.2.2. Route Origination and ReachableRoutes
Routes are injected into TRIP by a method outside the scope of this
specification. Possible methods include a front-end protocol, an
intra-domain routing protocol, or static configuration.
5.2.3. Route Selection and ReachableRoutes
The routes in ReachableRoutes are necessary for route selection.
5.2.4. Aggregation and ReachableRoutes
To aggregate multiple routes, the set of ReachableRoutes to be
aggregated MUST combine to form a less specific set.
There is no mechanism within TRIP to communicate that a particular
address prefix is not used and thus that these addresses could be
skipped during aggregation. LSs MAY use methods outside of TRIP to
learn of invalid prefixes that may be ignored during aggregation.
If an LS advertises an aggregated route, it MUST include the
AtomicAggregate attribute.
5.2.5. Route Dissemination and ReachableRoutes
The ReachableRoutes attribute is recomputed at each LS except where
flooding is being used (e.g., within a domain). It is therefore
possible for an LS to change the Application Protocol field of a
route before advertising that route to an external peer.
If an LS changes the Application Protocol of a route it advertises,
it MUST include the ConvertedRoute attribute in the UPDATE message.
5.2.6. Aggregation Specifics for Decimal Routing Numbers, E.164 Numbers,
and PentaDecimal Routing Numbers
An LS that has routes to all valid numbers in a specific prefix
SHOULD advertise that prefix as the ReachableRoutes, even if there
are more specific prefixes that do not actually exist on the PSTN.
Generally, it takes 10 Decimal Routing/E.164 prefixes, or 15
PentaDecimal Routing prefixes, of length n to aggregate into a prefix
of length n-1. However, if an LS is aware that a prefix is an
invalid Decimal Routing/E.164 prefix, or PentaDecimal Routing prefix,
then the LS MAY aggregate by skipping this prefix. For example, if
the Decimal Routing prefix 19191 is known not to exist, then an LS
can aggregate to 1919 without 19191. A prefix representing an
invalid set of PSTN destinations is sometimes referred to as a
"black-hole." The method by which an LS is aware of black-holes is
not within the scope of TRIP, but if an LS has such knowledge, it can
use the knowledge when aggregating.
5.3. NextHopServer
Conditional Mandatory: True (if ReachableRoutes and/or
WithdrawnRoutes attribute is present).
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 3.
Given a route with application protocol A and destinations D, the
NextHopServer indicates to the next-hop that messages of protocol A
destined for D should be sent to it. This may or may not represent
the ultimate destination of those messages.
5.3.1. NextHopServer Syntax
For generality, the address of the next-hop server may be of various
types (domain name, IPv4, IPv6, etc). The NextHopServer attribute
includes the ITAD number of next-hop server, a length field, and a
next-hop name or address.
The syntax for the NextHopServer is given in Figure 13.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Next Hop ITAD |
+---------------+---------------+--------------+----------------+
| Length | Server (variable) ...
+---------------+---------------+--------------+----------------+
Figure 13: NextHopServer Syntax
The Next-Hop ITAD indicates the domain of the next-hop. Length field
gives the number of octets in the Server field, and the Server field
contains the name or address of the next-hop server. The server
field is represented as a string of ASCII characters. It is defined
as follows:
Server = host [":" port ]
host = < A legal Internet host domain name
or an IPv4 address using the textual representation
defined in Section 2.1 of RFC1123 [9]
or an IPv6 address using the textual representation
defined in Section 2.2 of RFC2373 [10]. The IPv6
address MUST be enclosed in "[" and "]"
characters.>
port = *DIGIT
If the port is empty or not given, the default port is assumed (e.g.,
port 5060 if the application protocol is SIP).
5.3.2. Route Origination and NextHopServer
When an LS originates a routing object into TRIP, it MUST include a
NextHopServer within its domain. The NextHopServer could be an
address of the egress gateway or of a signaling proxy.
5.3.3. Route Selection and NextHopServer
LS policy may prefer certain next-hops or next-hop domains over
others.
5.3.4. Aggregation and NextHopServer
When aggregating multiple routing objects into a single routing
object, an LS MUST insert a new signaling server from within its
domain as the new NextHopServer unless all of the routes being
aggregated have the same next-hop.
5.3.5. Route Dissemination and NextHopServer
When propagating routing objects to peers, an LS may choose to insert
a signaling proxy within its domain as the new next-hop, or it may
leave the next-hop unchanged. Inserting a new next-hop will cause
the signaling messages to be sent to that address, and will provide
finer control over the signaling path. Leaving the next-hop
unchanged will yield a more efficient signaling path (fewer hops).
It is a local policy decision of the LS to decide whether to
propagate or change the NextHopServer.
5.4. AdvertisementPath
Conditional Mandatory: True (if ReachableRoutes and/or
WithdrawnRoutes attribute is present).
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 4.
This attribute identifies the ITADs through which routing information
carried in an advertisement has passed. The AdvertisementPath
attribute is analogous to the AS_PATH attribute in BGP. The
attributes differ in that BGP's AS_PATH also reflects the path to the
destination. In TRIP, not every domain need modify the next-hop, so
the AdvertisementPath may include many more hops than the actual path
to the destination. The RoutedPath attribute (Section 5.5) reflects
the actual signaling path to the destination.
5.4.1. AdvertisementPath Syntax
AdvertisementPath is a variable length attribute that is composed of
a sequence of ITAD path segments. Each ITAD path segment is
represented by a type-length-value triple.
The path segment type is a 1-octet long field with the following
values defined:
Value Segment Type
1 AP_SET: unordered set of ITADs a route in the
advertisement message has traversed
2 AP_SEQUENCE: ordered set of ITADs a route in
the advertisement message has traversed
The path segment length is a 1-octet long field containing the number
of ITADs in the path segment value field.
The path segment value field contains one or more ITAD numbers, each
encoded as a 4-octets long field. ITAD numbers uniquely identify an
Internet Telephony Administrative Domain, and must be obtained from
IANA. See Section 13 for procedures to obtain an ITAD number from
IANA.
5.4.2. Route Origination and AdvertisementPath
When an LS originates a route then:
- The originating LS shall include its own ITAD number in the
AdvertisementPath attribute of all advertisements sent to LSs
located in neighboring ITADs. In this case, the ITAD number of
the originating LS's ITAD will be the only entry in the
AdvertisementPath attribute.
- The originating LS shall include an empty AdvertisementPath
attribute in all advertisements sent to LSs located in its own
ITAD. An empty AdvertisementPath attribute is one whose length
field contains the value zero.
5.4.3. Route Selection and AdvertisementPath
The AdvertisementPath may be used for route selection. Possible
criteria to be used are the number of hops on the path and the
presence or absence of particular ITADs on the path.
As discussed in Section 10, the AdvertisementPath is used to prevent
routing information from looping. If an LS receives a route with its
own ITAD already in the AdvertisementPath, the route MUST be
discarded.
5.4.4. Aggregation and AdvertisementPath
The rules for aggregating AdvertisementPath attributes are given in
the following sections, where the term "path" used in Section 5.4.4.1
and 5.4.4.2 is understood to mean AdvertisementPath.
5.4.4.1. Aggregating Routes with Identical Paths
If all routes to be aggregated have identical path attributes, then
the aggregated route has the same path attribute as the individual
routes.
5.4.4.2. Aggregating Routes with Different Paths
For the purpose of aggregating path attributes we model each ITAD
within the path as a pair <type, value>, where "type" identifies a
type of the path segment (AP_SEQUENCE or AP_SET), and "value" is the
ITAD number. Two ITADs are said to be the same if their
corresponding <type, value> are the same.
If the routes to be aggregated have different path attributes, then
the aggregated path attribute shall satisfy all of the following
conditions:
- All pairs of the type AP_SEQUENCE in the aggregated path MUST
appear in all of the paths of routes to be aggregated.
- All pairs of the type AP_SET in the aggregated path MUST appear
in at least one of the paths of the initial set (they may
appear as either AP_SET or AP_SEQUENCE types).
- For any pair X of the type AP_SEQUENCE that precedes pair Y in
the aggregated path, X precedes Y in each path of the initial
set that contains Y, regardless of the type of Y.
- No pair with the same value shall appear more than once in the
aggregated path, regardless of the pair's type.
An implementation may choose any algorithm that conforms to these
rules. At a minimum, a conformant implementation MUST be able to
perform the following algorithm that meets all of the above
conditions:
- Determine the longest leading sequence of tuples (as defined
above) common to all the paths of the routes to be aggregated.
Make this sequence the leading sequence of the aggregated path.
- Set the type of the rest of the tuples from the paths of the
routes to be aggregated to AP_SET, and append them to the
aggregated path.
- If the aggregated path has more than one tuple with the same
value (regardless of tuple's type), eliminate all but one such
tuple by deleting tuples of the type AP_SET from the aggregated
path.
An implementation that chooses to provide a path aggregation
algorithm that retains significant amounts of path information may
wish to use the procedure of Section 5.4.4.3.
5.4.4.3. Example Path Aggregation Algorithm
An example algorithm to aggregate two paths works as follows:
- Identify the ITADs (as defined in Section 5.4.1) within each
path attribute that are in the same relative order within both
path attributes. Two ITADs, X and Y, are said to be in the
same order if either X precedes Y in both paths, or if Y
precedes X in both paths.
- The aggregated path consists of ITADs identified in (a) in
exactly the same order as they appear in the paths to be
aggregated. If two consecutive ITADs identified in (a) do not
immediately follow each other in both of the paths to be
aggregated, then the intervening ITADs (ITADs that are between
the two consecutive ITADs that are the same) in both attributes
are combined into an AP_SET path segment that consists of the
intervening ITADs from both paths; this segment is then placed
in between the two consecutive ITADs identified in (a) of the
aggregated attribute. If two consecutive ITADs identified in
(a) immediately follow each other in one attribute, but do not
follow in another, then the intervening ITADs of the latter are
combined into an AP_SET path segment; this segment is then
placed in between the two consecutive ITADs identified in (a)
of the aggregated path.
If as a result of the above procedure a given ITAD number appears
more than once within the aggregated path, all but the last instance
(rightmost occurrence) of that ITAD number should be removed from the
aggregated path.
5.4.5. Route Dissemination and AdvertisementPath
When an LS propagates a route which it has learned from another LS,
it shall modify the route's AdvertisementPath attribute based on the
location of the LS to which the route will be sent.
- When a LS advertises a route to another LS located in its own
ITAD, the advertising LS MUST NOT modify the AdvertisementPath
attribute associated with the route.
- When a LS advertises a route to an LS located in a neighboring
ITAD, then the advertising LS MUST update the AdvertisementPath
attribute as follows:
* If the first path segment of the AdvertisementPath is of
type AP_SEQUENCE, the local system shall prepend its own
ITAD number as the last element of the sequence (put it in
the leftmost position).
* If the first path segment of the AdvertisementPath is of
type AP_SET, the local system shall prepend a new path
segment of type AP_SEQUENCE to the AdvertisementPath,
including its own ITAD number in that segment.
5.5. RoutedPath
Conditional Mandatory: True
(if ReachableRoutes attribute is present).
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 5.
This attribute identifies the ITADs through which messages sent using
this route would pass. The ITADs in this path are a subset of those
in the AdvertisementPath.
5.5.1. RoutedPath Syntax
The syntax of the RoutedPath attribute is the same as that of the
AdvertisementPath attribute. See Section 5.4.1.
5.5.2. Route Origination and RoutedPath
When an LS originates a route it MUST include the RoutedPath
attribute.
- The originating LS shall include its own ITAD number in the
RoutedPath attribute of all advertisements sent to LSs located
in neighboring ITADs. In this case, the ITAD number of the
originating LS's ITAD will be the only entry in the RoutedPath
attribute.
- The originating LS shall include an empty RoutedPath attribute
in all advertisements sent to LSs located in its own ITAD. An
empty RoutedPath attribute is one whose length field contains
the value zero.
5.5.3. Route Selection and RoutedPath
The RoutedPath MAY be used for route selection, and in most cases is
preferred over the AdvertisementPath for this role. Some possible
criteria to be used are the number of hops on the path and the
presence or absence of particular ITADs on the path.
5.5.4. Aggregation and RoutedPath
The rules for aggregating RoutedPath attributes are given in Section
5.4.4.1 and 5.4.4.2, where the term "path" used in Section 5.4.4.1
and 5.4.4.2 is understood to mean RoutedPath.
5.5.5. Route Dissemination and RoutedPath
When an LS propagates a route that it learned from another LS, it
modifies the route's RoutedPath attribute based on the location of
the LS to which the route is sent.
- When an LS advertises a route to another LS located in its own
ITAD, the advertising LS MUST NOT modify the RoutedPath
attribute associated with the route.
- If the LS has not changed the NextHopServer attribute, then the
LS MUST NOT change the RoutedPath attribute.
- Otherwise, the LS changed the NextHopServer and is advertising
the route to an LS in another ITAD. The advertising LS MUST
update the RoutedPath attribute as follows:
* If the first path segment of the RoutedPath is of type
AP_SEQUENCE, the local system shall prepend its own ITAD
number as the last element of the sequence (put it in the
leftmost position).
* If the first path segment of the RoutedPath is of type
AP_SET, the local system shall prepend a new path segment of
type AP_SEQUENCE to the RoutedPath, including its own ITAD
number in that segment.
5.6. AtomicAggregate
Conditional Mandatory: False.
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 6.
The AtomicAggregate attribute indicates that a route may traverse
domains not listed in the RoutedPath. If an LS, when presented with
a set of overlapping routes from a peer LS, selects the less specific
route without selecting the more specific route, then the LS includes
the AtomicAggregate attribute with the routing object.
5.6.1. AtomicAggregate Syntax
This attribute has length zero (0); the value field is empty.
5.6.2. Route Origination and AtomicAggregate
Routes are never originated with the AtomicAggregate attribute.
5.6.3. Route Selection and AtomicAggregate
The AtomicAggregate attribute may be used in route selection - it
indicates that the RoutedPath may be incomplete.
5.6.4. Aggregation and AtomicAggregate
If any of the routes to aggregate has the AtomicAggregate attribute,
then so MUST the resultant aggregate.
5.6.5. Route Dissemination and AtomicAggregate
If an LS, when presented with a set of overlapping routes from a peer
LS, selects the less specific route (see Section 0) without selecting
the more specific route, then the LS MUST include the AtomicAggregate
attribute with the routing object (if it is not already present).
An LS receiving a routing object with an AtomicAggregate attribute
MUST NOT make the set of destinations more specific when advertising
it to other LSs, and MUST NOT remove the attribute when propagating
this object to a peer LS.
5.7. LocalPreference
Conditional Mandatory: False.
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 7.
The LocalPreference attribute is only used intra-domain, it indicates
the local LS's preference for the routing object to other LSs within
the same domain. This attribute MUST NOT be included when
communicating to an LS in another domain, and MUST be included over
intra-domain links.
5.7.1. LocalPreference Syntax
The LocalPreference attribute is a 4-octet unsigned numeric value. A
higher value indicates a higher preference.
5.7.2. Route Origination and LocalPreference
Routes MUST NOT be originated with the LocalPreference attribute to
inter-domain peers. Routes to intra-domain peers MUST be originated
with the LocalPreference attribute.
5.7.3. Route Selection and LocalPreference
The LocalPreference attribute allows one LS in a domain to calculate
a preference for a route, and to communicate this preference to other
LSs within the domain.
5.7.4. Aggregation and LocalPreference
The LocalPreference attribute is not affected by aggregation.
5.7.5. Route Dissemination and LocalPreference
An LS MUST include the LocalPreference attribute when communicating
with peer LSs within its own domain. An LS MUST NOT include the
LocalPreference attribute when communicating with LSs in other
domains. LocalPreference attributes received from inter-domain peers
MUST be ignored.
5.8. MultiExitDisc
Conditional Mandatory: False.
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 8.
When two ITADs are connected by more than one set of peers, the
MultiExitDisc attribute may be used to specify preferences for routes
received over one of those links versus routes received over other
links. The MultiExitDisc parameter is used only for route selection.
5.8.1. MultiExitDisc Syntax
The MultiExitDisc attribute carries a 4-octet unsigned numeric value.
A higher value represents a more preferred routing object.
5.8.2. Route Origination and MultiExitDisc
Routes originated to intra-domain peers MUST NOT be originated with
the MultiExitDisc attribute. When originating a route to an inter-
domain peer, the MultiExitDisc attribute may be included.
5.8.3. Route Selection and MultiExitDisc
The MultiExitDisc attribute is used to express a preference when
there are multiple links between two domains. If all other factors
are equal, then a route with a higher MultiExitDisc attribute is
preferred over a route with a lower MultiExitDisc attribute.
5.8.4. Aggregation and MultiExitDisc
Routes with differing MultiExitDisc parameters MUST NOT be
aggregated. Routes with the same value in the MultiExitDisc
attribute MAY be aggregated and the same MultiExitDisc attribute
attached to the aggregated object.
5.8.5. Route Dissemination and MultiExitDisc
If received from a peer LS in another domain, an LS MAY propagate the
MultiExitDisc to other LSs within its domain. The MultiExitDisc
attribute MUST NOT be propagated to LSs in other domains.
An LS may add the MultiExitDisc attribute when propagating routing
objects to an LS in another domain. The inclusion of the
MultiExitDisc attribute is a matter of policy, as is the value of the
attribute.
5.9. Communities
Conditional Mandatory: False.
Required Flags: Not Well-Known, Independent Transitive.
Potential Flags: None.
TRIP Type Code: 9.
A community is a group of destinations that share some common
property.
The Communities attribute is used to group destinations so that the
routing decision can be based on the identity of the group. Using
the Communities attribute should significantly simplify the
distribution of routing information by providing an administratively
defined aggregation unit.
Each ITAD administrator may define the communities to which a
particular route belongs. By default, all routes belong to the
general Internet Telephony community.
As an example, the Communities attribute could be used to define an
alliance between a group of Internet Telephony service providers for
a specific subset of routing information. In this case, members of
that alliance would accept only routes for destinations in this group
that are advertised by other members of the alliance. Other
destinations would be more freely accepted. To achieve this, a
member would tag each route with a designated Community attribute
value before disseminating it. This relieves the members of such an
alliance, from the responsibility of keeping track of the identities
of all other members of that alliance.
Another example use of the Communities attribute is with aggregation.
It is often useful to advertise both the aggregate route and the
component more-specific routes that were used to form the aggregate.
These information components are only useful to the neighboring TRIP
peer, and perhaps the ITAD of the neighboring TRIP peer, so it is
desirable to filter out the component routes. This can be achieved
by specifying a Community attribute value that the neighboring peers
will match and filter on. That way it can be assured that the more
specific routes will not propagate beyond their desired scope.
5.9.1. Syntax of Communities
The Communities attribute is of variable length. It consists of a
set of 8-octet values, each of which specifies a community. The
first 4 octets of the Community value are the Community ITAD Number
and the next 4 octets are the Community ID.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Community ITAD Number 1 |
+---------------+---------------+--------------+----------------+
| Community ID 1 |
+---------------+---------------+--------------+----------------+
| . . . . . . . . .
+---------------+---------------+--------------+----------------+
Figure 14: Communities Syntax
For administrative assignment, the following assumptions may be made:
The Community attribute values starting with a Community ITAD
Number of 0x00000000 are hereby reserved.
The following communities have global significance and their
operation MUST be implemented in any Community attribute-aware TRIP
LS.
- NO_EXPORT (Community ITAD Number = 0x00000000 and Community ID
= 0xFFFFFF01). Any received route with a community attribute
containing this value MUST NOT be advertised outside of the
receiving TRIP ITAD.
Other community values MUST be encoded using an ITAD number in the
four most significant octets. The semantics of the final four octets
(the Community ID octets) may be defined by the ITAD (e.g., ITAD 690
may define research, educational, and commercial community IDs that
may be used for policy routing as defined by the operators of that
ITAD).
5.9.2. Route Origination and Communities
The Communities attribute is not well-known. If a route has a
Communities attribute associated with it, the LS MUST include that
attribute in the advertisement it originates.
5.9.3. Route Selection and Communities
The Communities attribute may be used for route selection. A route
that is a member of a certain community may be preferred over another
route that is not a member of that community. Likewise, routes
without a certain community value may be excluded from consideration.
5.9.4. Aggregation and Communities
If a set of routes is to be aggregated and the resultant aggregate
does not carry an Atomic_Aggregate attribute, then the resulting
aggregate should have a Communities attribute that contains the union
of the Community attributes of the aggregated routes.
5.9.5. Route Dissemination and Communities
An LS may manipulate the Communities attribute before disseminating a
route to a peer. Community attribute manipulation may include adding
communities, removing communities, adding a Communities attribute (if
none exists), deleting the Communities attribute, etc.
5.10. ITAD Topology
Conditional Mandatory: False.
Required Flags: Well-known, Link-State encapsulated.
Potential Flags: None.
TRIP Type Code: 10.
Within an ITAD, each LS must know the status of other LSs so that LS
failure can be detected. To do this, each LS advertises its internal
topology to other LSs within the domain. When an LS detects that
another LS is no longer active, the information sourced by that LS
can be deleted (the Adj-TRIB-In for that peer may be cleared). The
ITAD Topology attribute is used to communicate this information to
other LSs within the domain.
An LS MUST send a topology update each time it detects a change in
its internal peer set. The topology update may be sent in an UPDATE
message by itself or it may be piggybacked on an UPDATE message which
includes ReachableRoutes and/or WithdrawnRoutes information.
When an LS receives a topology update from an internal LS, it MUST
recalculate which LSs are active within the ITAD via a connectivity
algorithm on the topology.
5.10.1. ITAD Topology Syntax
The ITAD Topology attribute indicates the LSs with which the LS is
currently peering. The attribute consists of a list of the TRIP
Identifiers with which the LS is currently peering, the format is
given in Figure 15. This attribute MUST use the link-state
encapsulation as defined in Section 4.3.2.4.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| TRIP Identifier 1 |
+---------------+---------------+--------------+----------------+
| TRIP Identifier 2 ... |
+---------------+---------------+--------------+----------------+
Figure 15: ITAD Topology Syntax
5.10.2. Route Origination and ITAD Topology
The ITAD Topology attribute is independent of any routes in the
UPDATE. Whenever the set of internal peers of an LS changes, it MUST
create an UPDATE with the ITAD Topology Attribute included listing
the current set of internal peers. The LS MUST include this
attribute in the first UPDATE it sends to a peer after the peering
session is established.
5.10.3. Route Selection and ITAD Topology
This attribute is independent of any routing information in the
UPDATE. When an LS receives an UPDATE with an ITAD Topology
attribute, it MUST compute the set of LSs currently active in the
domain by performing a connectivity test on the ITAD topology as
given by the set of originated ITAD Topology attributes. The LS MUST
locally purge the Adj-TRIB-In for any LS that is no longer active in
the domain. The LS MUST NOT propagate this purging information to
other LSs as they will make a similar decision.
5.10.4. Aggregation and ITAD Topology
This information is not aggregated.
5.10.5. Route Dissemination and ITAD Topology
An LS MUST ignore the attribute if received from a peer in another
domain. An LS MUST NOT send this attribute to an inter-domain peer.
5.11. ConvertedRoute
Conditional Mandatory: False.
Required Flags: Well-known.
Potential Flags: None.
TRIP Type Code: 12.
The ConvertedRoute attribute indicates that an intermediate LS has
altered the route by changing the route's Application Protocol. For
example, if an LS receives a route with Application Protocol X and
changes the Application Protocol to Y before advertising the route to
an external peer, the LS MUST include the ConvertedRoute attribute.
The attribute is an indication that the advertised application
protocol will not be used end-to-end, i.e., the information
advertised about this route is not complete.
5.11.1. ConvertedRoute Syntax
This attribute has length zero (0); the value field is empty.
5.11.2. Route Origination and ConvertedRoute
Routes are never originated with the ConvertedRoute attribute.
5.11.3. Route Selection and ConvertedRoute
The ConvertedRoute attribute may be used in route selection - it
indicates that advertised routing information is not complete.
5.11.4. Aggregation and ConvertedRoute
If any of the routes to aggregate has the ConvertedRoute attribute,
then so MUST the resultant aggregate.
5.11.5. Route Dissemination and ConvertedRoute
If an LS changes the Application Protocol of a route before
advertising the route to an external peer, the LS MUST include the
ConvertedRoute attribute.
5.12. Considerations for Defining New TRIP Attributes
Any proposal for defining new TRIP attributes should specify the
following:
- the use of this attribute,
- the attribute's flags,
- the attribute's syntax,
- how the attribute works with route origination,
- how the attribute works with route aggregation, and
- how the attribute works with route dissemination and the
attribute's scope (e.g., intra-domain only like
LocalPreference)
IANA will manage the assignment of TRIP attribute type codes to new
attributes.
6. TRIP Error Detection and Handling
This section describes errors to be detected and the actions to be
taken while processing TRIP messages.
When any of the conditions described here are detected, a
NOTIFICATION message with the indicated Error Code, Error Subcode,
and Data fields MUST be sent, and the TRIP connection MUST be closed.
If no Error Subcode is specified, then a zero Subcode MUST be used.
The phrase "the TRIP connection is closed" means that the transport
protocol connection has been closed and that all resources for that
TRIP connection have been de-allocated. If the connection was
inter-domain, then routing table entries associated with the remote
peer MUST be marked as invalid. Routing table entries MUST NOT be
marked as invalid if an internal peering session is terminated. The
fact that the routes have been marked as invalid is passed to other
TRIP peers before the routes are deleted from the system.
Unless specified explicitly, the Data field of the NOTIFICATION
message that is sent to indicate an error MUST be empty.
6.1. Message Header Error Detection and Handling
All errors detected while processing the Message Header are indicated
by sending the NOTIFICATION message with the Error Code Message
Header Error. The Error Subcode elaborates on the specific nature of
the error. The error checks in this section MUST be performed by
each LS upon receipt of every message.
If the Length field of the message header is less than 3 or greater
than 4096, or if the Length field of an OPEN message is less than the
minimum length of the OPEN message, or if the Length field of an
UPDATE message is less than the minimum length of the UPDATE message,
or if the Length field of a KEEPALIVE message is not equal to 3, or
if the Length field of a NOTIFICATION message is less than the
minimum length of the NOTIFICATION message, then the Error Subcode
MUST be set to Bad Message Length. The Data field contains the
erroneous Length field.
If the Type field of the message header is not recognized, then the
Error Subcode MUST be set to "Bad Message Type." The Data field
contains the erroneous Type field.
6.2. OPEN Message Error Detection and Handling
All errors detected while processing the OPEN message are indicated
by sending the NOTIFICATION message with the Error Code "OPEN Message
Error." The Error Subcode elaborates on the specific nature of the
error. The error checks in this section MUST be performed by each LS
upon receipt of every OPEN message.
If the version number contained in the Version field of the received
OPEN message is not supported, then the Error Subcode MUST be set to
"Unsupported Version Number." The Data field is a 1-octet unsigned
integer, which indicates the largest locally supported version
number, which is less than the version of the remote TRIP peer bid
(as indicated in the received OPEN message).
If the ITAD field of the OPEN message is unacceptable, then the Error
Subcode MUST be set to "Bad Peer ITAD." The determination of
acceptable ITAD numbers is outside the scope of this protocol.
If the Hold Time field of the OPEN message is unacceptable, then the
Error Subcode MUST be set to "Unacceptable Hold Time." An
implementation MUST reject Hold Time values of one or two seconds.
An implementation MAY reject any proposed Hold Time. An
implementation that accepts a Hold Time MUST use the negotiated value
for the Hold Time.
If the TRIP Identifier field of the OPEN message is not valid, then
the Error Subcode MUST be set to "Bad TRIP Identifier." A TRIP
identifier is 4-octets in length and can take any value. An LS
considers the TRIP Identifier invalid if it already has an open
connection with another peer LS that has the same ITAD and TRIP
Identifier.
Any two LSs within the same ITAD MUST NOT have equal TRIP Identifier
values. This restriction does not apply to LSs in different ITADs
since the purpose is to uniquely identify an LS using its TRIP
Identifier and its ITAD number.
If one of the Optional Parameters in the OPEN message is not
recognized, then the Error Subcode MUST be set to "Unsupported
Optional Parameters."
If the Optional Parameters of the OPEN message include Capability
Information with an unsupported capability (unsupported in either
capability type or value), then the Error Subcode MUST be set to
"Unsupported Capability," and the entirety of the unsupported
capabilities MUST be listed in the Data field of the NOTIFICATION
message.
If the Optional Parameters of the OPEN message include Capability
Information which does not match the receiving LS's capabilities,
then the Error Subcode MUST be set to "Capability Mismatch," and the
entirety of the mismatched capabilities MUST be listed in the Data
field of the NOTIFICATION message.
6.3. UPDATE Message Error Detection and Handling
All errors detected while processing the UPDATE message are indicated
by sending the NOTIFICATION message with the Error Code "UPDATE
Message Error." The Error Subcode elaborates on the specific nature
of the error. The error checks in this section MUST be performed by
each LS upon receipt of every UPDATE message. These error checks
MUST occur before flooding procedures are invoked with internal
peers.
If any recognized attribute has Attribute Flags that conflict with
the Attribute Type Code, then the Error Subcode MUST be set to
"Attribute Flags Error." The Data field contains the erroneous
attribute (type, length and value).
If any recognized attribute has an Attribute Length that conflicts
with the expected length (based on the attribute type code), then the
Error Subcode MUST be set to "Attribute Length Error." The Data
field contains the erroneous attribute (type, length and value).
If any of the mandatory (i.e., conditional mandatory attribute and
the conditions for including it in the UPDATE message are fulfilled)
well-known attributes are not present, then the Error Subcode MUST be
set to "Missing Well-known Mandatory Attribute." The Data field
contains the Attribute Type Code of the missing well-known
conditional mandatory attributes.
If any of the well-known attributes are not recognized, then the
Error Subcode MUST be set to "Unrecognized Well-known Attribute."
The Data field contains the unrecognized attribute (type, length and
value).
If any attribute has a syntactically incorrect value, or an undefined
value, then the Error Subcode is set to "Invalid Attribute." The
Data field contains the incorrect attribute (type, length and value).
Such a NOTIFICATION message is sent, for example, when a
NextHopServer attribute is received with an invalid address.
The information carried by the AdvertisementPath attribute is checked
for ITAD loops. ITAD loop detection is done by scanning the full
AdvertisementPath, and checking that the ITAD number of the local
ITAD does not appear in the AdvertisementPath. If the local ITAD
number appears in the AdvertisementPath, then the route MAY be stored
in the Adj-TRIB-In. However unless the LS is configured to accept
routes with its own ITAD in the advertisement path, the route MUST
not be passed to the TRIP Decision Process. The operation of an LS
that is configured to accept routes with its own ITAD number in the
advertisement path are outside the scope of this document.
If the UPDATE message was received from an internal peer and either
the WithdrawnRoutes, ReachableRoutes, or ITAD Topology attribute does
not have the Link-State Encapsulation flag set, then the Error
Subcode is set to "Invalid Attribute" and the data field contains the
attribute. Likewise, the attribute is invalid if received from an
external peer and the Link-State Flag is set.
If any attribute appears more than once in the UPDATE message, then
the Error Subcode is set to "Malformed Attribute List."
6.4. NOTIFICATION Message Error Detection and Handling
If a peer sends a NOTIFICATION message, and there is an error in that
message, there is unfortunately no means of reporting this error via
a subsequent NOTIFICATION message. Any such error, such as an
unrecognized Error Code or Error Subcode, should be noticed, logged
locally, and brought to the attention of the administration of the
peer. The means to do this, however, are outside the scope of this
document.
6.5. Hold Timer Expired Error Handling
If a system does not receive successive messages within the period
specified by the negotiated Hold Time, then a NOTIFICATION message
with a "Hold Timer Expired" Error Code MUST be sent and the TRIP
connection MUST be closed.
6.6. Finite State Machine Error Handling
An error detected by the TRIP Finite State Machine (e.g., receipt of
an unexpected event) MUST result in sending a NOTIFICATION message
with the Error Code "Finite State Machine Error" and the TRIP
connection MUST be closed.