draft-ietf-ospf-mt-05.txt   draft-ietf-ospf-mt-06.txt 
Network Working Group P. Psenak Network Working Group P. Psenak
Internet-Draft S. Mirtorabi Internet-Draft S. Mirtorabi
Expires: July 16, 2006 A. Roy Expires: August 5, 2006 A. Roy
L. Nguyen L. Nguyen
P. Pillay-Esnault P. Pillay-Esnault
Cisco Systems Cisco Systems
January 12, 2006 February 1, 2006
Multi-Topology (MT) Routing in OSPF Multi-Topology (MT) Routing in OSPF
draft-ietf-ospf-mt-05.txt draft-ietf-ospf-mt-06.txt
Status of this Memo Status of this Memo
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have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on July 16, 2006. This Internet-Draft will expire on August 5, 2006.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This draft describes an extension to OSPF in order to define This draft describes an extension to OSPF in order to define
independent IP topologies called Multi-Topologies (MTs). The MT independent IP topologies called Multi-Topologies (MTs). The MT
extension can be used for computing different paths for unicast extension can be used for computing different paths for unicast
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metric for default topology will be advertised. metric for default topology will be advertised.
The unused T-bit is defined as the MT-bit in the option field in The unused T-bit is defined as the MT-bit in the option field in
order to assure that a multi-topology link-excluding capable router order to assure that a multi-topology link-excluding capable router
will only form an adjacency with another similarly configured router. will only form an adjacency with another similarly configured router.
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
|DN |O |DC |EA |NP |MC |E |MT | |DN |O |DC |EA |NP |MC |E |MT |
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
MT-bit: This bit MUST be set in Hello and Database Description MT-bit: If DefaultExclusionCapability is enable, this bit MUST
packets only if DefaultExclusionCapability is enabled be set in Hello packets and SHOULD be set in Database
(see Section 4.2) Description packet (see Section 4.2).
4.2 New Area Data Structure Parameter 4.2 New Area Data Structure Parameter
We define a new parameter in the Area Data Structure: We define a new parameter in the Area Data Structure:
DefaultExclusionCapability DefaultExclusionCapability
This configurable parameter ensures that all routers in an area This configurable parameter ensures that all routers in an area
have this capability enabled before the default topology can be have this capability enabled before the default topology can be
disabled on a router link in the area without causing backward disabled on a router link in the area without causing backward
compatibility problems. compatibility problems.
When an area data structure is created the DefaultExclusionCapability When an area data structure is created the DefaultExclusionCapability
is disabled by default. is disabled by default.
If DefaultExclusionCapability is disabled: If DefaultExclusionCapability is disabled:
o The MT-bit MUST be cleared in Hello and Database Description o The MT-bit MUST be cleared in Hello packet and SHOULD be cleared
packets. in Database Description packets.
o If a link participates in a non-default topology, it is o If a link participates in a non-default topology, it is
automatically included in the default topology to support backward automatically included in the default topology to support backward
compatibility between MT and non-MT routers. This is accomplished compatibility between MT and non-MT routers. This is accomplished
through advertisement via the TOS0 metric field the same as in through advertisement via the TOS0 metric field the same as in
standard OSPF [OSPF]. standard OSPF [OSPF].
If DefaultExclusionCapability is enabled: If DefaultExclusionCapability is enabled:
o The MT-bit MUST be set in Hello and Database Description packets o The MT-bit MUST be set in Hello and SHOULD be set in Database
Description packets
o The router will only accept a Hello or Database Description packet o The router will only accept a Hello packet if the MT-bit is set
if the MT-bit is set (see Section 4.3) (see Section 4.3)
When DefaultExclusionCapability is set to enabled a router is said to When DefaultExclusionCapability is set to enabled a router is said to
be operating in DefaultExclusionCapability mode. be operating in DefaultExclusionCapability mode.
4.3 Adjacency Formation with Link Exclusion Capability 4.3 Adjacency Formation with Link Exclusion Capability
In order to have a smooth transition from a non-MT area to an MT- In order to have a smooth transition from a non-MT area to an MT-
area, an MT router with DefaultExclusionCapability disabled will form area, an MT router with DefaultExclusionCapability disabled will form
adjacencies with non-MT routers and will include all links as part of adjacencies with non-MT routers and will include all links as part of
default topology. default topology.
A link may cease participating in default topology if A link may cease participating in default topology if
DefaultExclusionCapability is set to enabled. In this state, a DefaultExclusionCapability is set to enabled. In this state, a
router will only form adjacency with routers that set the MT-bit in router will only form adjacency with routers that set the MT-bit in
their Hello and Database Description packets. This will ensure that their Hello packets. This will ensure that all routers have
all routers have DefaultExclusionCapability enabled before the DefaultExclusionCapability enabled before the default topology can be
default topology can be disabled on a link. disabled on a link.
Receiving OSPF Hello packets as defined in section 10.5 of [OSPF] is Receiving OSPF Hello packets as defined in section 10.5 of [OSPF] is
modified as follows: modified as follows:
o If the DefaultExclusionCapability in the Area Data structure is o If the DefaultExclusionCapability in the Area Data structure is
set to enabled, Hello packets are discarded if the the received set to enabled, Hello packets are discarded if the the received
packet does not have the MT-bit set in the header options. packet does not have the MT-bit set in the header options.
Receiving OSPF Database Description packets as defined in section Receiving OSPF Database Description packets as defined in section
10.6 of [OSPF] is modified as follows: 10.6 of [OSPF] is unchanged. While packet options are validated in
hello packets, the only option checking performed for Database
If the DefaultExclusionCapability in the Area Data structure is Description packets is assuring that the options do not change during
set to enabled, Database Description packets are discarded if the the database exchange process.
the received packet does not have the MT-bit set in the header
options. The neighbor state is not modified to allow a window of
RouterDeadInterval seconds where the neighbor's
DefaultExclusionCapability may be upgraded.
4.4 OSPF Control Packets Transmission Over Excluded Links 4.4 OSPF Control Packets Transmission Over Excluded Links
If DefaultExclusionCapability is enabled, the default topology can be If DefaultExclusionCapability is enabled, the default topology can be
disabled on an interface. Disabling the default topology on an disabled on an interface. Disabling the default topology on an
interface does not impact the installation of connected routes for interface does not impact the installation of connected routes for
the interface in the default topology. It only affects what a router the interface in the default topology. It only affects what a router
advertises in its Router-LSA. advertises in its Router-LSA.
This allows OSPF control packets to be sent and received over an This allows OSPF control packets to be sent and received over an
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metric is used to advertise the metric in the default topology. metric is used to advertise the metric in the default topology.
During the summary and external prefix calculation for the default During the summary and external prefix calculation for the default
topology the TOS0 metric is used for Summary-LSAs, NSSA-LSAs, and AS- topology the TOS0 metric is used for Summary-LSAs, NSSA-LSAs, and AS-
External-LSAs. External-LSAs.
5. Interoperability between MT Capable and Non-MT Capable Routers 5. Interoperability between MT Capable and Non-MT Capable Routers
The default metric field is mandatory in all LSAs (even when metric The default metric field is mandatory in all LSAs (even when metric
value is 0). Even when a link or prefix does not exist in the value is 0). Even when a link or prefix does not exist in the
default topology, a non-MT router can consider the zero value in the default topology, a non-MT router will consider the zero value in the
metric field as a valid metric and consider the link or prefix as metric field as a valid metric and consider the link or prefix as
part of the default topology. part of the default topology.
In order to prevent the above problem, an MT capable router will In order to prevent the above problem, an MT capable router will
include all links as part of the default topology. If links need to include all links as part of the default topology. If links need to
be removed from the default topology, an MT capable router MUST be be removed from the default topology, an MT capable router MUST be
configured in DefaultExclusionCapability mode. In this mode, configured in DefaultExclusionCapability mode. In this mode,
routers will assure that all other routers in the area are in the routers will assure that all other routers in the area are in the
DefaultExclusionCapability mode before considering the MT-ID#0 metric DefaultExclusionCapability mode before considering the MT-ID#0 metric
in the SPF calculation. Only then can the TOS0 metric field in in the SPF calculation. Only then can the TOS0 metric field in
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