Internet DRAFT - draft-ietf-idr-v6
draft-ietf-idr-v6
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Network Working Group Yakov Rekhter
Internet Draft T.J. Watson Research Center, IBM Corp.
Paul Traina
cisco Systems
November 1994
IDRP for IPv6
<draft-ietf-idr-v6-00.txt>
Status of this memo
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documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups. Note that other groups may also distribute
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current status of any Internet Draft.
1 Overview
IDRP [5] is defined as the protocol for exchange of Inter-Domain
routing information between routers to support forwarding of ISO 8473
(Connectionless Network Layer Protocol (CLNP))[6] packets.
The network reachability information exchanged via IDRP provides
sufficient information to detect routing loops and enforce routing
decisions based on performance preference and policy constraints as
outlined in RFC 1104 [1]. In particular, IDRP exchanges routing
information containing full domain-level paths and enforces routing
policies based on configuration information.
IDRP may be viewed as an extension of BGP-4 ([9], [10]) that provides
(among other things) much better scaling with respect to support for
routing information aggregation based on CIDR ([2], [11]), as well as
stronger capabilities for policy based routing (e.g. ability to
impose control over transit traffic). Enhanced scaling capabilities
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are provided via the concept of Routing Domain Confederations (RDCs),
that allow to express both topology and policy information in terms
of aggregates (confederations) rather than individual entities
(domains). IDRP also provides capability to carry reachability and
forwarding information associated with multiple network layer
protocols (e.g. IPv6, IPv4).
This document contains the adaptation of the IDRP protocol
definition that enables it to be used as a protocol for the exchange
of inter-domain system routing information among routers to support
the forwarding of IPv6 packets across multiple domains. We refer to
IDRP with this adaptation as "IDRP for IPv6". While this document
doesn't cover use of IDRP to support routing for other network layer
protocols (e.g. IPv4), it is expected that IDRP for IPv6 will be able
to operate in a multiprotocol environment as well.
2 Terminology
This document assumes that the reader is familiar with the following
documents:
- IPv6 protocol specification [3],
- IPv6 Addressing Architecture [4], and
- IDRP specification (IS 10747) [5].
A few definitions are in order to aid the reader:
BIS - a Boundary Intermediate System (or border router)
BISPDU - an IDRP message exchanged between a pair of BISs
ES - End System (host)
FIB - Forwarding Information Base (IP forwarding table)
IS - Intermediate System (router)
NET - Network Entity Title (a network layer address for a router)
NLRI - Network Layer Reachability Information (set of reachable
destinations)
NPDU - an IPv6 packet
NSAP - Network Service Access Point (a network layer address)
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PDU - a packet
SNPA - subnetwork point of attachment (Data Link address)
It is expected that the above definitions should be adequate for
understanding of IDRP. Familiarity with any of the documents listed
in the normative references of the protocol specifications (section 2
of [5]) is not required.
Unless stated otherwise here, any reference to the above terms in [5]
should be interpreted based on the above definitions.
3 The Adaptation Layer
The Inter-Domain Routing Protocol (IDRP) or, more formally,
"The Protocol for the Exchange of Inter-Domain Routing information
among Intermediate Systems to support Forwarding of ISO 8473 PDUs
(IDRP)"
is the inter-domain routing protocol defined to support the
forwarding of Connectionless Network Layer Protocol (CLNP) [6]
packets that traverse multiple routing domains.
IDRP document [5] covers both the protocol specifications and the
usage issues (which is in contrast to BGP-4 documentation that has a
separate document that defines the protocol [10], and a separate
document that describes the protocol's usage [9]).
While IDRP was developed within ISO, it makes few, if any, ISO-
specific assumptions. In particular, it does not require
participating domains to support any specific ISO Intra-Domain
protocol, such as IS-IS [7], nor does it require participating
routers to run ES-IS [8].
The only requirements imposed by the protocol on the participating
routers is that the protocol information can be exchanged among them
over a connectionless network layer (which in the case of OSI is
CLNP), and that the network layer connectivity between routers
within a single routing domain should be provided by means outside of
IDRP (e.g., via some intra-domain routing protocol). IDRP does not
place any restrictions on the structure of reachability information,
as long it can be expressed as an arbitrary set of variable length
address prefixes.
Since IPv6 can provide connectionless service between routers, and
since reachable IPv6 destinations can be expressed as IPv6 address
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prefixes, IDRP can be easily adapted to be an inter-domain routing
protocol which can be used in the IPv6 Internet.
The adaptation described in this document consists of:
- specifying the parts of the protocol that are not needed,
- specifying modifications/clarifications to certain parts of the
protocol to reflect IPv6 specifics and operational experience
with BGP-4,
- adding new features to reflect operational experience with
BGP-4.
4 Features in IDRP which shall not be implemented
The following lists the functions that shall not be implemented by
IDRP for IPv6 (all references are with respect to [5]):
- Support for distinguishing path attributes according to
sections 5.7, 7.11.2 and 7.11.3
- Transit Delay according to section 7.12.8
- Residual Error according to section 7.12.9
- Expense according to section 7.12.10
- Locally Defined QOS according to section 7.12.11
- Security according to section 7.12.14
- Priority according to section 7.12.16
- Procedures for detecting inconsistent routing decisions,
according to section 7.15.1
- Forwarding CLNP packets according to section 8
- The interface to CLNP according to section 9
- support of the Network Management information described in the
IDRP GDMO according to section 11
All the material presented in the sections listed above may be
ignored.
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5 Features in IDRP which shall be implemented
An implementation of IDRP for IPv6 shall contain all mandatory
features of IDRP, except those mentioned in section 4 of this
document. In addition, a BIS for IDRP for IPv6 shall implement the
following (all references are with respect to this document):
- an interface to the IPv6 protocol, as described in section 5.1
- the ability to identify and extract IPv6 reachability and
forwarding information as described in sections 5.2 and 5.3
- Modifications to the ROUTE_SEPARATOR and
MULTI_EXIT_DISCRIMINATOR path attributes, as described in
section 5.4
- Support for the ATOMIC_AGGREGATE path attribute, as described
in section 5.5
- Modifications to the RD_PATH attribute update process, as
described in section 5.6
- Modifications to the tie-breaking procedures, as described in
sections 5.7 and 5.8
- Modifications to handling Hold Time, as described in section
5.9
- Constructing forwarding address (next hop), as described in
section 5.10
Naming and addressing conventions discussed in sections 5.10, 5.11
and 7.1 of [5] do not apply to IDRP for IPv6, and thus should be
ignored. Section 6 of this document contains the material that
covers naming and addressing conventions for IDRP for IPv6.
Deployment guidelines for IDRP for IPv6 are specified in section 7 of
this document. These guidelines supersede the material presented in
section 7.2 of [5].
Domain configuration information for IDRP for IPv6 is defined in
section 8 of this document. The material of that section supersedes
the material presented in section 7.3 of [5].
5.1 An interface to IPv6
This sections supersedes the material in section 7.5 of [5].
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IDRP information is carried between a pair of BISs in the form of
BISPDUs. For IDRP for IPv6 these BISPDUs are carried in the data
field of IPv6 packets of protocol type 45.
IDRP relies on IPv6 to perform the initial processing of incoming
BISPDUs. The IPv6 protocol machine shall process inbound packets
according to the appropriate IPv6 functions.
If a fixed header of an IPv6 packet contains a protocol type that
identifies IDRP, and the packet's source address identifies any
system listed in managed objects internalBIS or externalBISNeighbor,
then the packet contains a BISPDU. The BISPDU shall be passed to the
IDRP finite state machine defined in section 7.6.1 of [5].
5.2 Encoding IPv6 reachability information
NLRI carried by the UPDATE PDU has an indication of the protocol
family for the destinations depicted by the NLRI. The indication is
encoded in the Proto_type, Proto_length and Protocol fields (see
section 6.3.2 of [5]).
To carry IPv6 address prefixes an implementation of IDRP for IPv6
shall use the following values in the NLRI:
Proto_Type:
[TBD]
Proto_Length:
[TBD]
Protocol:
[TBD]
Addr_Length:
variable (the value shall be between 0 and 128)
Addr_Info:
This is a variable length field that contains a list of IPv6
address prefixes for the routes that are being advertised.
Each IPv6 address prefix is encoded as a 2-tuple of the form
<length, prefix>, whose fields are described below:
+---------------------------+
| Length (1 octet) |
+---------------------------+
| Prefix (variable) |
+---------------------------+
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The use and the meaning of these fields are as follows:
a) Length:
The Length field indicates the length in bits of the IPv6
address prefix. A length of zero indicates a prefix that
matches all IPv6 addresses (with prefix, itself, of zero
octets).
b) Prefix:
The Prefix field contains IPv6 address prefixes followed by
enough trailing bits to make the end of the field fall on an
octet boundary. Note that the value of trailing bits is
irrelevant.
An implementation of IDRP for IPv6 shall ignore any NLRI indicating a
different protocol type.
5.3 Encoding IPv6 forwarding information
IPv6 forwarding information is carried in the NEXT_HOP path
attribute. The attribute has a Proto_type, Proto_Length and Protocol
fields which indicate the protocol family for the address of the
NEXT_HOP (see section 6.3.1.4 of [5]). An implementation of IDRP for
IPv6 shall have the following values in the NEXT_HOP field:
Proto_Type:
[TBD]
Proto_Length:
[TBD]
Protocol:
[TBD]
Length of NET: 16
NET of Next Hop: an IPv6 unicast address
SNPA information: as appropriate for the subnetwork type in use
An implementation of IDRP for IPv6 should ignore any NEXT_HOP
information indicating a different protocol type.
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5.4 Modification to the existing path attributes
To facilitate operations, IDRP for IPv6 modifies the following path
attributes:
- LOCAL_PREF field in the ROUTE_SEPARATOR attribute (see section
6.3.1.1) is changed from 1 octet to 4 octets. As a result the
length of the ROUTE_SEPARATOR attribute is changed from 5 to 8
octets.
- The length of the MULTI_EXIT_DISCRIMINATOR attribute is changed
from 1 octet to 4 octets.
Semantics, as well as handling of the modified attributes is left
intact.
5.5 New path attributes
IDRP for IPv6 defines the following new attribute:
AGGREGATOR (Type Code 17)
AGGREGATOR is an optional transitive attribute of length 32.
The attribute contains the last RDI that formed the
aggregate route (encoded as 16 octets), followed by the IPv6
address of the BIS that formed the aggregate route (encoded
as 16 octets). The BIS that formed the aggregate route may
decline to encode its address and instead insert a value of
all zeros into that field.
The attribute may be included in routes which are formed by
route aggregation. A BIS that performs the aggregation may
add the AGGREGATOR attribute which shall contain BIS's own
RDI and IPv6 address.
ATOMIC_AGGREGATE (Type Code 18)
ATOMIC_AGGREGATE is a well-known discretionary attribute of
length 0. It is used by a BIS to inform other BISs that the
local system selected for advertisement a less specific
route without selecting a more specific route which is
included in it.
If a BIS, when presented with a set of overlapping routes
from one of its peers, selects the less specific route
without selecting the more specific one, then the local
system shall attach the ATOMIC_AGGREGATE attribute to the
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route when propagating it to other BISs (if that attribute
is not already present in the received less specific route).
A BIS that receives a route with the ATOMIC_AGGREGATE
attribute shall not remove the attribute from the route when
propagating it to other BISs. A BIS that receives a route
with the ATOMIC_AGGREGATE attribute shall not make any NLRI
of that route more specific when advertising this route to
other BISs. A BIS that receives a route with the
ATOMIC_AGGREGATE attribute needs to be cognizant of the fact
that the actual path to destinations, as specified in the
NLRI of the route, while having the loop-free property, may
traverse domains/confederations that are not listed in the
RD_PATH attribute.
5.6 Modifications to the RD_PATH attribute update procedures
The only difference between the way how the RD_PATH attribute
handling is specified in [5] and the way how it is specified in this
document is the rule for adding domain's own RDI to the RD_PATH
attribute. In [5] the RDI is added when a route is received from a
BIS in adjacent RD, or when a BIS originates a route. This document
specifies that the RDI is added when a route is advertised to a BIS
in adjacent RD. The following is the exact text of sections 7.12.3.1
through 7.12.3.3 of [5], except for the modifications governing the
rules for adding domain's own RDI.
5.6.1 Generating an RD_PATH attribute
This section supersedes the material in section 7.12.3.1 of [5].
When a BIS originates a route to destinations contained within its
own routing domain or to destinations learned by means outside the
protocol (see 7.12.2 of [5]), it shall examine the information
contained in its managed object rdcConfig to determine the ordering
relationships among all the confederations of which the local routing
domain is a member. The local BIS shall then construct an RD_PATH
attribute as follows:
a) If the local routing domain is a member of one or more
confederations, the RD_PATH shall consist of an ENTRY_SEQ
segment followed immediately by an RD_SEQ segment. The
ENTRY_SEQ shall list the confederations, ordered as follows:
1) If a confederation, RDC-B, is nested within another
confederation, RDC-A, then the RDI of RDC-A shall precede
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that of RDC-B.
2) The RDIs of overlapping confederations shall be listed in
increasing order of the RDIs, as long as the order implied
by any nesting relationships is maintained. For purposes of
ordering, two RDIs are compared octet-by-octet from the left
until differing octet values are found. The RDI with the
lesser octet value (when treated as an unsigned integer) is
considered to have the lesser RDI value. If there are two
RDIs of different lengths, and the leading octets of the
longer RDI are exactly the same as the octets of the
(complete) shorter RDI, then the shorter RDI is considered
to have the lesser value.
The RD_SEQ shall be empty.
b) If the local routing domain is not a member of any
confederation, then the RD_PATH contains a single RD_SEQ
segment that shall be empty.
5.6.2 Updating a received RD_PATH attribute
This section supersedes the material in section 7.12.3.2 of [5].
The local BIS shall update the RD_PATH attribute of a route received
from another BIS according to the following rules:
a) If the route was received from a BIS located in the same
routing domain as the local BIS, then the RD_PATH attribute
shall not be updated.
b) If the route was received from a BIS located in an adjacent
routing domain, the local BIS shall determine if the route has
entered any confederations (see 7.13.3), and it shall examine
the information contained in its managed object rdcConfig to
determine the ordering relationships among all such
confederations. The local BIS shall then amend the RD_PATH
attribute as follows:
1) If the route has entered any confederations, the BIS shall
append a path segment of type ENTRY_SEQ that lists all the
newly entered confederations, ordered as follows:
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i) If a confederation, RDC-B, is nested within another
confederation, RDC-A, then the RDI of RDC-A shall precede
that of RDC-B.
ii) The RDIs of overlapping confederations shall be listed in
increasing order of the RDIs, as long as the order
implied by any nesting relationships is maintained. For
purposes of ordering, two RDIs are compared octet-by-
octet from the left until differing octet values are
found. The RDI with the lesser octet value (when treated
as an unsigned integer) is considered to have the lesser
RDI value. If there are two RDIs of different lengths,
and the leading octets of the longer RDI are exactly the
same as the octets of the (complete) shorter RDI, then
the shorter RDI is considered to have the lesser value.
5.6.3 Advertising a route received from another BIS
This section supersedes the material in section 7.12.3.3 of [5].
After receiving a route, a BIS will have modified its RD_PATH
attribute in accordance with section 5.6.1 of this document; and when
a route is generated locally, the BIS will have created an RD_PATH
attribute in accordance with section 5.6.2 of this document. If the
local BIS selects a route (that was either originated locally or was
received from another BIS) for subsequent advertisement, the RD_PATH
attribute of that route shall be amended as follows, based on the
confederations which have been exited and on the nesting
relationships among confederations of which the local BIS is a member
(see managed object rdcConfig):
a) If the adjacent BIS to which the route will be advertised is in
adjacent domain, then the local BIS shall append a path segment
of type RD_SEQ that lists the RDI of the local BIS's domain.
b) If the adjacent BIS to which the route will be advertised can
be reached without exiting any confederations, then no
modification to the RD_PATH attribute shall be made.
c) If the adjacent BIS to which the route will be advertised can
only be reached by exiting one or more confederations, then the
local BIS shall check the RD_PATH attribute for the presence of
ENTRY_SEQ or ENTRY_SET path segments that contain the RDIs of
the exited confederations.
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If there is any RDI of an exited confederation which is absent
from all ENTRY_SEQ and ENTRY_SET segments, then the route is in
error. The local BIS shall send an IDRP ERROR PDU to the BIS
that advertised the route, reporting a Misconfigured_RDCs
error.
If two confederation, RDC-A and RDC-B, are listed in the same
ENTRY_SEQ, and managed object rdcConfig indicates that RDC-B is
nested within RDC-A, then the RDI of RDC-A shall precede that
of RDC-B in the ENTRY_SEQ. If it does not, the local BIS shall
send an IDRP ERROR to the BIS that advertised the route,
reporting a Misconfigured_RDCs error.
Otherwise, the local BIS shall scan the RD_PATH attribute from
the back (right to left, starting at the highest numbered
octet) looking for an ENTRY_SEQ or ENTRY_SET path segment that
lists an exited confederation. Within a given ENTRY_SET or
ENTRY_SEQ segment, the RDI for a given confederation can not be
processed until the RDIs for all confederations nested within
it have been processed.
For each exited confederation (for example, the confederation
whose RDI is "X"), the advertising BIS shall then update the
RD_PATH of the route as follows:
1) The entry for "X" shall be removed from the ENTRY_SEQ or
ENTRY_SET segment
2) If "X" is the only RDI contained in an ENTRY_SEQ or
ENTRY_SET segment of the RD_PATH, then create a path segment
of type RD_SEQ that lists "X" and insert it in front of the
previous entry for "X".
3) If the local BIS's routing domain is a member of other
confederations besides "X" that are listed in the ENTRY_SEQ
or ENTRY_SET segments of the RD_PATH, then:
i) If "X" occurs in an ENTRY_SEQ or ENTRY_SET segment, and
"X" is nested within none of the other confederations,
then create an RD_SET that lists "X" and insert it in
front of the first ENTRY_SEQ or ENTRY_SET segment that
occurs in the RD_PATH.
ii) If "X" occurs in an ENTRY_SEQ and "X" is nested within
all the other confederations, then create a path segment
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of type RD_SEQ that lists "X" and insert it immediately
in front of the previous entry for "X"
iii) If "X" occurs in an ENTRY_SEQ and "X" is nested within
some but not all of the other confederations, then create
a path segment of type RD_SET that lists "X", and insert
it immediately after the closest prior entry for any
confederation in which "X" is nested.
iv) If "X" occurs in an ENTRY_SET and "X" is nested within
all the other confederations, then create a path segment
of type RD_SET that lists "X" and insert it immediately
in front of the previous entry for "X"
v) If "X" occurs in an ENTRY_SET and "X" is nested within
some but not all of the other confederations, then create
a path segment of type RD_SET that lists "X", and insert
it immediately after the the closest prior entry for any
confederation in which "X" is nested.
If the procedures call for the insertion of an RD_SET or an
RD_SEQ between entries that are contained in a single ENTRY_SET
or ENTRY_SEQ, then break the ENTRY_SET or ENTRY_SEQ into two
segments of identical type and perform the insertion. For
example, if it is necessary to insert RD_SET(X) between entries
for "A" and "B", where "A" and "B" are contained in
ENTRY_SEQ(H,J,A,B,C), the result would be: ENTRY_SEQ(H,J,A)
RD_SET(X) ENTRY_SEQ(B,C).
If, after applying these procedures, the ENTRY_SEQ or ENTRY_SET
segment in which "X" originally occurred is empty, then that path
segment shall be deleted, together with any subsequent path
segments between itself and the next occurring ENTRY_SEQ or
ENTRY_SET segment, or between itself and the end of the RD_PATH
attribute if there is no subsequent ENTRY_SEQ or ENTRY_SET
segment.
5.7 Modifications to tie-breaking procedures for phase 2
This section supersedes the material in section 7.16.2.1 of [5].
In its Adj-RIBs-In a BIS may have several routes to the same
destination that have the same degree of preference. The local BIS
can select only one of these routes for inclusion in the associated
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Loc-RIB. The local BIS considers all equally preferable routes, both
those received from BISs located in adjacent RDs, and those received
from other BISs located in the local BIS's own RD.
The following tie-breaking procedure assumes that for each candidate
route all the BISs within an RD can ascertain the cost of a path
(interior distance) to the address depicted by the NEXT_HOP attribute
of the route. Ties shall be broken according to the following
algorithm:
a) If the local BIS is configured to take into account
MULTI_EXIT_DISC, and the candidate routes differ in their
MULTI_EXIT_DISC attribute, select the route that has the lowest
value of the MULTI_EXIT_DISC attribute.
b) Otherwise, select the route that has the lowest cost (interior
distance) to the entity depicted by the NEXT_HOP attribute of the
route. If there are several routes with the same cost, then the
tie-breaking shall be broken as follows:
- if at least one of the candidate routes was advertised by the
BIS in an adjacent RD, select the route that was advertised by
the BIS in an adjacent RD whose address has the lowest value
among all other BIS in adjacent RDs;
- otherwise, select the route that was advertised by the BIS
whose address has the lowest value.
5.8 Modifications to tie-breaking procedures for internal updates
This section supersedes the material in section 7.17.1.1 of [5].
If a local BIS has connections to several BISs in adjacent domains,
there will be multiple Adj-RIBs-In associated with these BISs. These
Adj-RIBs-In might contain several equally preferable routes to the
same destination, all of which were advertised by BISs located in
adjacent domains. The local BIS shall select one of these routes
according to the following rules:
a) If the candidate route differ only in their NEXT_HOP and
MULTI_EXIT_DISC attributes, and the local BIS's managed object
Multiexit is TRUE, (the local BIS configured to take into account
MULTI_EXIT_DISC attribute), select the routes that has the lowest
value of the MULTI_EXIT_DISC attribute.
b) If the local BIS can ascertain the cost of a path to the entity
depicted by the NEXT_HOP attribute of the candidate route, select
the route with the lowest cost.
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c) In all other cases, select the route that was advertised by the
BIS whose address has the lowest value.
5.9 Modifications to handling Hold Time
Upon receipt of an OPEN BISPDU, a BIS must calculate the value of the
Hold Timer by using the smaller of its configured Hold Time and the
Hold Time received in the OPEN BISPDU.
IDRP for IPv6 requires the value of the Hold Time field carried in
the OPEN BISPDU to be either zero or at least 3 seconds. An
implementation must reject Hold Time values of one or two seconds.
An implementation may reject any proposed Hold Time. An
implementation which accepts a Hold Time must use the negotiated
value for the Hold Time. If the negotiated Hold Time interval is
zero, then periodic KEEPALIVE messages shall not be sent.
5.10 Determining the forwarding address (Next Hop)
Next hop forwarding information information associated with a
particular route shall be derived from the NEXT_HOP attribute in the
UPDATE BISPDU that carries the route. If that attribute is not
present, the next hop (forwarding address) shall be derived from the
source IPv6 address of the IPv6 packet that carries the UPDATE BISPDU
containing the route.
In addition to the procedures for handling the NEXT_HOP attribute
specified in section 7.12.4 of [5], IDRP for IPv6 specifies the
following:
- A BIS must never advertise an address of a peer to that peer as
a NEXT_HOP, for a route that the speaker is originating.
- A BIS must never install a route with itself as the next hop.
- When a BIS advertises the route to a BIS located in its own
domain, the advertising BIS should not modify the NEXT_HOP
attribute associated with the route.
- When a BIS receives the route from an internal neighbor BIS, it
may use the NEXT_HOP address as the forwarding address,
provided that the address is on a common subnet with the local
BIS.
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6 Naming and addressing conventions
This section supersedes the material of sections 5.10, 5.11 and 7.1
of [5].
IDRP for IPv6 does not assume or require any particular structure for
IPv6 addresses. That is, as long as the domain administrator assigns
addresses that are consistent with the deployment constraints of
section 7 of this document, the protocol will operate correctly.
IPv6 address prefixes provide a compact way for identifying groups of
systems that reside in a given domain or confederation. A prefix may
have a length that is either smaller than, or the same size as the
IPv6 address (an IPv6 address is a special case of an address
prefix). The length of an encoded prefix is specified in bits.
Each routing domain and routing domain confederation whose BIS(s)
implement IDRP for IPv6 shall have an unambiguous routing domain
identifier (RDI), which is an IPv6 address prefix.
An RDI is assigned statically and does not change based on the
operational status of a routing domain. An RDI identifies routing
domain or confederation uniquely, but does not necessarily convey any
information about policies or identities of its members.
7 Deployment guidelines
This section supersedes the material in section 7.2 of [5].
Hosts and routers may use any IPv6 unicast addresses, provided that
these addresses are globally unambiguous. However correct and
efficient operation of this protocol can only be guaranteed if the
address assignment reflects the actual topology -- addresses are
topologically significant. One possible architecture for IPv6 address
assignment that satisfies this requirement is described in [12].
8 Domain Configuration Information
Correct Operation of IDRP described in [5] assumes that a minimum
amount of information is available to both the inter-domain and
intra-domain routing protocols. This information is static in
nature, and is not expected to change frequently. This document
assumes that this information is supplied via IDRP MIB. While the
following in phrased in terms of MIB, this document allows
alternative mechanisms (e.g. configuration files) as well.
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The information required by a BIS that implements the IDRP for IPv6
protocol is:
a) Location and identity of adjacent Intra-Domain routers:
The MIB table IntraIS lists the IPv6 addresses of the routers
to which the local BIS may deliver an inbound NPDU whose
destination lies within the BIS's routing domain. These routers
listed in the IntraIS table support the intra-domain routing
protocol of this domain, and share at least one common subnet
with the BIS.
In particular, if the local BIS participates in both the
inter-domain routing protocol (IDRP) and the intra-domain
routing protocol, then the IPv6 address of the local BIS will
be listed in the IntraIS table.
b) Location and identity of BISs in the BIS's domain:
This information permits a BIS to identify all other BISs
located within its routing domain. This information is
contained in the MIB table InternalBIS, which contains a set of
IPv6 addresses which identify the BISs in the domain.
c) Location and identity of BISs in adjacent domains:
Each BIS needs information to identify the IPv6 address of each
BIS located in an adjacent RD and reachable via a single
subnetwork hop. This information is contained in the IDRP MIB
table externalBISNeighbor, which is a table of IPv6 addresses.
d) IPv6 network address information for all systems in the routing
domain:
This information is used by the BIS to construct its network
layer reachability information. This information is contained
in the MIB table internalSystems, which lists NLRI (expressed
as address prefixes) of the systems within the routing domain.
e) Local RDI:
This information is contained in managed object localRDI; it is
the RDI of the routing domain in which the BIS is located.
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f) RDC-Config:
This information identifies all the routing domain
confederations (RDCs) to which the RD of the local BIS belongs,
and it describes the nesting relationships that are in force
between them. It is contained in the MIB table rdcConfig.
Note that since a domain is not required to belong to a
confederation this information is optional and needs to be
present only at BISs of the domains that are part of one or
more of RDCs.
9 Multiple IDRP sessions between the same pair of routers
An IPv6 router may have multiple IPv6 addresses, one for each
interface. In contrast, an OSI Intermediate System has only one
Network Entity Title (network address). An OSI BIS thus may not have
multiple IDRP sessions with another BIS, since the NET is unique and
there is no mechanism for multiplexing sessions. However, an IPv6
router may potentially have multiple IDRP sessions with another
router, since each BIS may have multiple IPv6 addresses, and one BIS
may not be able to ascertain that those addresses correspond to the
same BIS. Multiple IDRP sessions between BISs may not be efficient,
but they are not illegal, nor do they impact the robustness of the
IDRP for IPv6 protocol; they will simply appear as multiple paths to
the same neighboring domain. One possible way of avoiding multiple
parallel IDRP sessions between a pair of BISs within a single domain
is to bind all source addresses of outgoing BISPDUs to the IPv6
address of a particular interface (either physical or logical) of the
BIS. Likewise, for a pair of BISs located in adjacent domains,
binding the source addresses to a single address of an interface
attached to a common subnetwork allows for the elimination of
multiple parallel sessions.
10 Required set of supported routing policies
Policies are provided to IDRP in the form of configuration
information. This information is not directly encoded in the
protocol. Therefore, IDRP can provide support for very complex
routing policies (an example of such policy is presented in Annex K
of [5]). However, it is not required that all IDRP implementations
support such policies.
We are not attempting to standardize the routing policies that must
be supported in every IDRP implementation; we strongly encourage all
implementors to support the following set of routing policies:
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1. IDRP implementations should allow a domain to control
announcements of IDRP-learned routes to adjacent domains.
Implementations should also support such control with at least
the granularity of a single address prefix. Implementations
should also support such control with the granularity of a
domain, where the domain may be either the domain that
originated the route, or the domain that advertised the route
to the local system (adjacent domain). Care must be taken when
a BIS selects a new route that can't be announced to a
particular external peer, while the previously selected route
was announced to that peer. Specifically, the local system
must explicitly indicate to the peer that the previous route is
now infeasible.
2. IDRP implementations should allow a domain to prefer a
particular path to a destination (when more than one path is
available). At the minimum an implementation shall support
this functionality by allowing to administratively assign a
degree of preference to a route based solely on the IPv6
address of the neighbor the route is received from. The
allowed range of the assigned degree of preference shall be
between 0 and 2^(31) - 1.
3. IDRP implementations should allow a domain to ignore routes
with certain domains in the RD_PATH path attribute. Such
function can be implemented by assigning "infinity" as
"weights" for such domains. The route selection process must
ignore routes that have "weight" equal to "infinity".
11 Operations over Switched Virtual Circuits
When using IDRP for IPv6 over Switched Virtual Circuit (SVC)
subnetworks it may be desirable to minimize traffic generated by
IDRP. Specifically, it may be desirable to eliminate traffic
associated with periodic KEEPALIVE messages. IDRP for IPv6 includes
a mechanism for operation over switched virtual circuit (SVC)
services which avoids keeping SVCs permanently open and allows it to
eliminates periodic sending of KEEPALIVE messages.
This section describes how to operate without periodic KEEPALIVE
messages to minimize SVC usage when using an intelligent SVC circuit
manager. The proposed scheme may also be used on "permanent"
circuits, which support a feature like link quality monitoring or
echo request to determine the status of link connectivity.
The mechanism described in this section is suitable only between the
BISs that are directly connected over a common virtual circuit.
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11.1 Establishing an IDRP Connection
The feature is selected by specifying zero Hold Time in the OPEN
BISPDU.
11.2 Circuit Manager Properties
The circuit manager must have sufficient functionality to be able to
compensate for the lack of periodic KEEPALIVE BISPDU:
- It must be able to determine link layer unreachability in a
predictable finite period of a failure occurring.
- On determining unreachability it should:
- start a configurable dead timer (comparable to a
typical Hold timer value).
- attempt to re-establish the Link Layer connection.
- If the dead timer expires it should:
- send a deactivate indication to IDRP FSM.
- If the connection is re-established it should:
- cancel the dead timer.
- transmit any queued BISPDUs.
11.3 Combined Properties
Some implementations may not be able to guarantee that the IDRP
process and the circuit manager will operate as a single entity; i.e.
they can have a separate existence when the other has been stopped or
has crashed.
If this is the case, a periodic two-way poll between the IDRP process
and the circuit manager should be implemented. If the IDRP process
discovers the circuit manager has gone away it should close all
relevant BIS-BIS connections. If the circuit manager discovers the
IDRP process has gone away it should close all its BIS-BIS
connections associated with the IDRP process and reject any further
incoming BIS-BIS connections.
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12 Modifications to the conformance clause
To reflect the list of functions that shall not be implemented (see
section 4 of this document) the following items in the IDRP
conformance clause (section 12.1 of [5]) shall not be implemented:
- clause (d): Transit Delay, Residual Error, Expense, Locally
Defined QOS, Security, Priority
- clause (m)
- clause (r)
- clause (s)
- clause (t)
13 Modifications to PICS
The PICS (Protocol Implementation Conformance Statement) provides a
convenient and concise mechanism to define which function need and
need not be implemented for IDRP for IPv6. All references in this
section are with respect to [5].
All items with PICS Status as Optional need not be implemented in
IDRP for IPv6. In addition, IDRP for IPv6 should not support the
following items (even if some of the items are listed as Mandatory):
Table A.4.3:
MGT
Table A.4.5:
INCONS
Table A.4.8:
PSRCRT, DATTS, MATCH
Table A.4.11:
TDLY, RERR, EXP, LQOSG, SECG, PRTY
Table A.4.12:
TDLYP, RERRP, EXPP, LQOSP, SECP, PRTYP
Table A.4.13:
TDLYR, RERRR, EXPR, LQOSR, SECR, PRTYR
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Implementation of all other items with Optional Status not listed in
the previous paragraph is optional.
14 Navigating through IDRP
Here is the list of sections in [5] that are relevant to the IDRP
for IPv6 implementation: chapters 1, 3, 4, 5 (except 5.10 and 5.11),
6, 7 (except for 7.1, 7.2, 7.3, 7.4, 7.12.3, 7.12.8, 7.12.9, 7.12.10,
7.12.11 and 7.12.16), 10. The rest of the material in [5] could be
safely ignored.
15 Security Considerations
Security issues are not discussed in this document.
16 Acknowledgements
Large parts of this document are borrowed from the BGP Protocol
specifications and BGP Usage documents ([9], [10]).
We would like to thank Susan Hares (MERIT) and John Scudder (MERIT)
for their work on IDRP for IPv4. Portions of this document are
borrowed from their work.
We would like to thank Tony Li (cisco Systems) for his review of this
document.
Finally we would like to thank the whole Inter-Domain Routing (IDR)
Working Group for their contribution to this document.
17 References
[1] Braun, H-W., "Models of Policy Based Routing", RFC 1104,
Merit/NSFNET, June 1989.
[2] Fuller, V., Li, T., Yu, J., Varadhan, K., "Classless Inter-Domain
Routing (CIDR): an Address Assignment and Aggregation Strategy", RFC
1519, September 1993
[3] Hinden, B., "Internet Protocoli, Version 6 (IPv6) Specification",
Internet Draft, October 1994
[4] Hinden, B., "IP Next Generation Addressing Architecture",
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Internet Draft, October 1994
[5] ISO/IEC IS 10747 - Information Processing Systems -
Telecommunications and Information Exchange between Systems -
Protocol for Exchange of Inter-domain Routing Information among
Intermediate Systems to Support Forwarding of ISO 8473 PDUs, 1993
[6] ISO 8473 - Information Processing Systems - Data Communications
- Protocol for Providing the Connectionless-mode Network Service,
1988.
[7] ISO/IEC 10589 - Information Processing Systems -
Telecommunications and Information Exchange between systems -
Intermediate System to Intermediate System Intra-Domain routing
information exchange protocol for use in conjunction with the
Protocol for providing the Connectionless-mode Network Service (ISO
8473), 1992.
[8] ISO 9542 - Information Processing Systems - Telecommunications
and information exchange between systems - End system to Intermediate
system routing exchange protocol for use in conjunction with the
Protocol for providing the connectionless-mode network service (ISO
8473)
[9] Rekhter, Y., Gross, P., ``Application of the Border Gateway
Protocol in the Internet'', RFC1655, July 1994
[10] Rekhter, Y., Li, T., ``A Border Gateway Protocol 4 (BGP-4)'',
RFC1654, July 1994
[11] Rekhter, Y., Li, T., "An Architecture for IP Address Allocation
with CIDR", RFC1518, September 1993
[12] Rekhter, Y., Li, T., "An Architecture for IPv6 Address
Allocation" Internet Draft, September 1994
Authors' Addresses
Yakov Rekhter
T.J. Watson Research Center, IBM Corporation
P.O. Box 704
Yorktown Heights, NY 10598
Phone: (914) 784-7361
email: yakov@watson.ibm.com
Paul Traina
cisco Systems, Inc.
170 W. Tasman Dr.
San Jose, CA 95134
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email: pst@cisco.com
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