draft-ietf-lsr-ospf-bfd-strict-mode-02.txt   draft-ietf-lsr-ospf-bfd-strict-mode-03.txt 
Link State Routing K. Talaulikar Link State Routing K. Talaulikar
Internet-Draft P. Psenak Internet-Draft P. Psenak
Intended status: Standards Track Cisco Systems, Inc. Intended status: Standards Track Cisco Systems, Inc.
Expires: July 3, 2021 A. Fu Expires: September 25, 2021 A. Fu
Bloomberg Bloomberg
M. Rajesh M. Rajesh
Juniper Networks Juniper Networks
December 30, 2020 March 24, 2021
OSPF Strict-Mode for BFD OSPF Strict-Mode for BFD
draft-ietf-lsr-ospf-bfd-strict-mode-02 draft-ietf-lsr-ospf-bfd-strict-mode-03
Abstract Abstract
This document specifies the extensions to OSPF that enable an OSPF This document specifies the extensions to OSPF that enable an OSPF
router to signal the requirement for a Bidirectional Forwarding router to signal the requirement for a Bidirectional Forwarding
Detection (BFD) session prior to adjacency formation. Link-Local Detection (BFD) session prior to adjacency formation. Link-Local
Signaling (LLS) is used to advertise this requirement of "strict- Signaling (LLS) is used to advertise the requirement of strict-mode
mode" of BFD session establishment for OSPF adjacency. If both OSPF for BFD session establishment for OSPF adjacency. If both OSPF
neighbors advertise the "strict-mode" of BFD, adjacency formation neighbors advertise the strict-mode for BFD, adjacency formation will
will be blocked until a BFD session has been successfully be blocked until a BFD session has been successfully established.
established.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 3, 2021. This Internet-Draft will expire on September 25, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
skipping to change at page 2, line 34 skipping to change at page 2, line 33
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8 10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 9 10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
Bidirectional Forwarding Detection (BFD) [RFC5880] enables routers to Bidirectional Forwarding Detection (BFD) [RFC5880] enables routers to
monitor dataplane connectivity and to detect faults in the monitor data-plane connectivity and to detect faults in the
bidirectional path between them. BFD is leveraged by routing bidirectional path between them. BFD is leveraged by routing
protocols like OSPFv2[RFC2328] and OSPFv3 [RFC5340] to detect protocols like OSPFv2 [RFC2328] and OSPFv3 [RFC5340] to detect
connectivity failures for established adjacencies and trigger the connectivity failures for established adjacencies and trigger the
rerouting of traffic around the failure more quickly than with OSPF rerouting of traffic around the failure faster than with OSPF hello
hello packet monitoring. packet monitoring.
The use of BFD for monitoring routing protocols adjacencies is The use of BFD for monitoring routing protocols adjacencies is
described in [RFC5882]. When BFD monitoring is enabled for OSPF described in [RFC5882]. When BFD monitoring is enabled for OSPF
adjacencies, the BFD session is bootstrapped based on the neighbor adjacencies, the BFD session is bootstrapped based on the neighbor
address information discovered by the exchange of OSPF hello packets. address information discovered by the exchange of OSPF Hello packets.
Faults in the bidirectional forwarding detected via BFD then result Faults in the bidirectional forwarding detected via BFD then result
in the OSPF adjacency being brought down. Note that it is possible in the OSPF adjacency being brought down. Note that it is possible
in some failure scenarios for the network to be in a state such that in some failure scenarios for the network to be in a state such that
an OSPF adjacency can be established but a BFD session cannot be an OSPF adjacency can be established but a BFD session cannot be
established and maintained. In certain other scenarios, a degraded established and maintained. In certain other scenarios, a degraded
or poor quality link may result in OSPF adjacency formation to or poor quality link will allow OSPF adjacency formation to succeed
succeed only to result in BFD session establishment not being but the BFD session establishment will fail or the BFD session will
successful or flapping of the BFD session. In this case, traffic flap. In this case, traffic that gets forwarded over such a link may
that gets forwarded over such a link may experience packet drops experience packet drops while the failure of the BFD session
while the failure of BFD session establishment would not enable fast establishment would not enable fast routing convergence if the link
routing convergence if the link were to go down or flap. were to go down or flap.
To avoid the routing churn associated with these scenarios, it would To avoid the routing churn associated with these scenarios, it would
be beneficial to not allow OSPF to establish an adjacency until a BFD be beneficial to not allow OSPF to establish an adjacency until a BFD
session is successfully established and has stabilized. However, session is successfully established and has stabilized. However,
this would preclude the OSPF operation in an environment in which not this would preclude the OSPF operation in an environment in which not
all OSPF routers support BFD and are enabled for BFD on the link. A all OSPF routers support BFD and are enabled for BFD on the link. A
solution is to block OSPF adjacency establishment until a BFD session solution is to block OSPF adjacency establishment until a BFD session
is established as long as both neighbors advertise such a is established as long as both neighbors advertise such a
requirement. Such a mode of OSPF BFD usage is referred to as requirement. Such a mode of OSPF BFD usage is referred to as
"strict-mode". "strict-mode".
This document specifies the OSPF protocol extensions using link-local This document specifies the OSPF protocol extensions using link-local
signaling (LLS) [RFC5613] for a router to indicate to its neighbor signaling (LLS) [RFC5613] for a router to indicate to its neighbor
the willingness to establish a BFD session in the "strict-mode". It the willingness to establish its adjacency using the strict-mode for
also introduces an extension for OSPFv3 link-local signaling of BFD. It also introduces an extension for OSPFv3 link-local signaling
interface IPv4 address when used for IPv4 address-family (AF) of the interface IPv4 address when used for an IPv4 address-family
instance to enable discovery of the IPv4 addresses for BFD session (AF) instance to enable discovery of the IPv4 addresses for BFD
setup. session setup.
A similar functionality for IS-IS is specified [RFC6213]. A similar functionality for IS-IS is specified [RFC6213].
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. LLS B-bit Flag 2. LLS B-bit Flag
This document defines the B-bit in the LLS Type 1 Extended Options This document defines the B-bit in the LLS Type 1 Extended Options
and Flags field. This bit is defined for the LLS block included in and Flags field. This bit is defined for the LLS block included in
Hello packets and indicates that BFD is enabled on the link and that Hello and Database Description (DD) packets and indicates that BFD is
the router requests BFD strict-mode. Section 7 describes the enabled on the link and that the router requests strict-mode for BFD.
position of the B-bit. Section 7 describes the position of the B-bit.
A router MUST include the LLS block with the LLS Type 1 Extended A router MUST include the LLS block with the LLS Type 1 Extended
Options and Flags TLV with the B-bit set its Hello messages when BFD Options and Flags TLV with the B-bit set in its Hello and DD packets
is enabled on the link. when strict-mode for BFD is enabled on the link.
3. Local Interface IPv4 Address TLV 3. Local Interface IPv4 Address TLV
The Local Interface IPv4 Address TLV is an LLS TLV meant for OSPFv3 The Local Interface IPv4 Address TLV is an LLS TLV defined for OSPFv3
protocol operations for IPv4 AF instances [RFC5838]. It has IPv4 AF instance [RFC5838] protocol operation. It has the following
following format: format:
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface IPv4 Address | | Local Interface IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where: where:
Type: 21 Type: 21
Length: 4 octet Length: 4 octet
Local Interface IPv4 Address: The primary IPv4 address of the Local Interface IPv4 Address: The primary IPv4 address of the
local interface. local interface.
4. Procedures 4. Procedures
A router supporting BFD strict-mode advertises this capability A router supporting strict-mode for BFD advertises this capability
through its hello messages as described in Section 2. When a router through its Hello packets as described in Section 2. When a router
supporting BFD strict-mode discovers a new neighbor router that also supporting strict-mode for BFD discovers a new neighbor router that
supports BFD strict-mode, then it will establish a BFD session first also supports strict-mode for BFD, then it will establish a BFD
with that neighbor before bringing up the OSPF adjacency as described session first with that neighbor before bringing up the OSPF
further in this section. adjacency as described further in this section.
This document updates the OSPF neighbor state machine as described in This document updates the OSPF neighbor state machine as described in
[RFC2328]. Specifically, the operations related to the Init state as [RFC2328]. Specifically, the operations related to the Init state as
below when BFD strict-mode is used: below when strict-mode for BFD is used:
Init (without BFD strict-mode) Init (without strict-mode for BFD)
In this state, a Hello packet has recently been received from the In this state, a Hello packet has recently been received from the
neighbor. However, bidirectional communication has not yet been neighbor. However, bidirectional communication has not yet been
established with the neighbor (i.e., the router itself did not established with the neighbor (i.e., the router itself did not
appear in the neighbor's Hello packet). All neighbors in this appear in the neighbor's Hello packet). All neighbors in this
state (or higher) are listed in the Hello packets sent from the state (or higher) are listed in the Hello packets sent from the
associated interface. associated interface.
Init (with BFD strict-mode) Init (with strict-mode for BFD)
In this state, an Hello packet has recently been received from the In this state, a Hello packet has recently been received from the
neighbor. However, bidirectional communication has not yet been neighbor. However, bidirectional communication has not yet been
established with the neighbor (i.e., the router itself did not established with the neighbor (i.e., the router itself did not
appear in the neighbor's Hello packet). A BFD session appear in the neighbor's Hello packet). BFD session establishment
establishment to the neighbor is requested, if not already done with the neighbor is requested, if not already completed (e.g., in
(e.g. in the event of transition from 2-way state). Neighbors in the event of transition from 2-way state). Neighbors in Init
Init state or higher will be listed in the Hello packets state or higher will be listed in the Hello packets associated
associated with the interface if they either have a corresponding with the interface if they either have a corresponding BFD session
BFD session established or have not advertised "strict-mode" BFD established or have not advertised strict-mode for BFD in the
in the Hello packet LLS Extended Options and Flags. Hello packet LLS Extended Options and Flags.
Whenever the neighbor state transitions to Down state, the removal of Whenever the neighbor state transitions to Down state, the removal of
the BFD session associated with that neighbor SHOULD be requested by the BFD session associated with that neighbor SHOULD be requested by
OSPF and subsequent BFD session establishment SHOULD similarly be OSPF and subsequent BFD session establishment SHOULD similarly be
requested by OSPF upon transitioning into Init state. This may requested by OSPF upon transitioning into Init state. This may
result in the deletion and creation of the BFD session respectively result in the deletion and creation of the BFD session respectively
when OSPF is the only client interested in the BFD session to the when OSPF is the only client interested in the BFD session with the
neighbor address. neighbor address.
An implementation MUST NOT wait for BFD session establishment in Init An implementation MUST NOT wait for BFD session establishment in Init
state unless BFD strict-mode is enabled on the router and the state unless strict-mode for BFD is enabled on the router and the
specific neighbor indicates BFD strict-mode capability via its Hello specific neighbor indicates strict-mode for BFD capability via its
LLS options. When BFD is enabled, but the strict-mode of operation Hello LLS options. When BFD is enabled, but the strict-mode for
has not be signaled by both neighbors, then an implementation SHOULD operation has not be signaled by both neighbors, then an
start the BFD session establishment only in 2-Way state or higher implementation SHOULD start the BFD session establishment only in
state. This makes it possible for an OSPF router to operate a mix of 2-Way state or higher state. This makes it possible for an OSPF
BFD operation in strict-mode or normal mode across different router to support BFD operation in both strict-mode and normal mode
interfaces or even different neighbors on the same multi-access LAN across different interfaces or even different neighbors on the same
interface. multi-access interface.
Once the OSPF state machine has moved beyond the Init state, any Once the OSPF state machine has moved beyond the Init state, any
change in the B-bit advertised in subsequent Hello messages MUST NOT change in the B-bit advertised in subsequent Hello packets MUST NOT
result in any trigger in either the OSPF adjacency or the BFD session result in any trigger in either the OSPF adjacency or the BFD session
management (i.e., the B-bit is considered only when in the Init management (i.e., the B-bit is considered only when in Init state).
state). Disabling BFD (or BFD strict-mode) on an OSPF router would Disabling BFD (or strict-mode for BFD) on an OSPF router would result
result in it not setting the B-bit in its subsequent Hello LLS in it not setting the B-bit in its subsequent Hello LLS options.
options. Disabling BFD strict-mode has no effect on the BFD Disabling strict-mode for BFD has no effect on the BFD operations and
operations and would not result in bringing down of any established would not result in bringing down of any established BFD session.
BFD session. Disabling BFD would result in the BFD session brought Disabling BFD would result in the BFD session being brought down due
down due to Admin reason and hence would not bring down the OSPF to Admin reason [RFC5882] and hence would not bring down the OSPF
adjacency. adjacency.
When BFD is enabled on an interface over which we already have an When BFD is enabled on an interface over which we already have an
existing OSPF adjacency, it would result in the router setting the existing OSPF adjacency, it would result in the router setting the
B-bit in its subsequent Hello messages. If the adjacency is already B-bit in its subsequent Hello packets. If the adjacency is already
up (i.e., in its terminal state of Full or 2-way with non-DR routers up (i.e., in its terminal state of Full or 2-way with non-DR routers
on a LAN) with a neighbor that also supports BFD strict-mode, then an on a multi-access interface) with a neighbor that also supports
implemantion SHOULD NOT bring this adjacency down but instead use the strict-mode for BFD, then an implementation SHOULD NOT bring this
BFD strict-mode of operation after the next transition into Init adjacency down but instead use the strict-mode for BFD operation
state. However, if the adjacency is not up, then an implementation after the next transition into Init state. However, if the adjacency
MAY bring such an adjacency down so it can use the BFD strict-mode is not up, then an implementation MAY bring such an adjacency down so
for its bring up. it can use the strict-mode for BFD for its adjacency establishment.
4.1. OSPFv3 IPv4 Address-Family Specifics 4.1. OSPFv3 IPv4 Address-Family Specifics
Multiple AF support in OSPFv3 [RFC5838] requires the use of an IPv6 Multiple AF support in OSPFv3 [RFC5838] requires the use of an IPv6
link-local address as the source address for hello packets even when link-local address as the source address for Hello packets even when
forming adjacencies for IPv4 AF instances. In most deployments of forming adjacencies for IPv4 AF instances. In most deployments of
OSPFv3 IPv4 AF, it is required that BFD is used to monitor and verify OSPFv3 IPv4 AF, it is required that BFD is used to monitor and verify
the IPv4 data plane connectivity between the routers on the link and, the IPv4 data plane connectivity between the routers on the link and,
hence, the BFD session is setup using IPv4 neighbor addresses. The hence, the BFD session is setup using IPv4 neighbor addresses. The
IPv4 neighbor address on the interface is learnt only later in the IPv4 neighbor address on the interface is learned only later in the
adjacency formation process when the neighbor's Link-LSA is received. adjacency formation process when the neighbor's Link-LSA is received.
This results in the setup of the BFD session either after the This results in the setup of the BFD session either after the
adjacency is established or later in the adjacency formation adjacency is established or later in the adjacency formation
sequence. sequence.
To enable BFD operation in strict-mode, it is necessary for an OSPF To enable operation in strict-mode for BFD, it is necessary for an
router to learned it's neighbor's IPv4 link address during the Init OSPF router to learn its neighbor's IPv4 link address during the Init
state of adjacency formation (ideally when it receives the first state of adjacency formation (ideally when it receives the first
hello). The use of the Local Interface IPv4 Address TLV (as defined hello). The use of the Local Interface IPv4 Address TLV (as defined
in Section 3) in the LLS block of the OSPFv3 Hello messages for IPv4 in Section 3) in the LLS block of the OSPFv3 Hello packets for IPv4
AF instances makes this possible. Implementations that support AF instances makes this possible. Implementations that support
strict-mode of BFD operation for OSPFv3 IPv4 AF instances MUST strict-mode for BFD operation for OSPFv3 IPv4 AF instances MUST
include the Local Interface IPv4 Address TLV in the LLS block of include the Local Interface IPv4 Address TLV in the LLS block of
their hello messages whenever the B-bit is also set in the LLS their Hello packets whenever the B-bit is also set in the LLS Options
Options and Flags field. A receiver MUST ignore the B-bit (i.e., not and Flags field. A receiver MUST ignore the B-bit (i.e., not operate
operate in BFD strict mode) when the Local Interface IPv4 Address TLV in BFD strict mode) when the Local Interface IPv4 Address TLV is not
is not present in OSPFv3 Hello message for IPv4 AF OSPFv3 instances. present in OSPFv3 Hello message for IPv4 AF OSPFv3 instances.
4.2. Graceful Restart Considerations 4.2. Graceful Restart Considerations
An implementation needs to handle scenarios where both graceful An implementation needs to handle scenarios where both graceful
restart (GR) and the strict-mode of BFD operation are deployed restart (GR) and the strict-mode for BFD operation are deployed
together. The GR aspects discussed in [RFC5882] also apply with together. The GR aspects discussed in [RFC5882] also apply with
strict-mode of BFD operation. Additionally, in strict-mode of BFD strict-mode for BFD operation. Additionally, in strict-mode for BFD
operation, since the OSPF adjacency formation is delayed until the operation, since the OSPF adjacency formation is delayed until the
BFD session establishment, the resultant delay in adjacency formation BFD session establishment, the resultant delay in adjacency formation
may affect or break the GR-based recovery. In such cases, it is may affect or break the GR-based recovery. In such cases, it is
RECOMMENDED that the GR timers are set such that they provide RECOMMENDED that the GR timers are set such that they provide
sufficient time to allow for normal BFD session establishment delays. sufficient time to allow for normal BFD session establishment delays.
5. Operations & Management Considerations 5. Operations & Management Considerations
An implementation SHOULD report the BFD session status along with the An implementation SHOULD report the BFD session status along with the
OSPF Init adjacency state when operating in BFD strict-mode and OSPF Init adjacency state when operating in strict-mode for BFD and
perform logging operations on state transitions to include the BFD perform logging operations on state transitions to include the BFD
events. This allows an operator to detect scenarios where an OSPF events. This allows an operator to detect scenarios where an OSPF
adjacency may be stuck waiting for BFD session establishment. adjacency may be stuck waiting for BFD session establishment.
In network deployments with noisy links or those with packet loss, In network deployments with noisy links or those with packet loss,
BFD sessions may flap frequently. In such scenarios, OSPF strict- BFD sessions may flap frequently. In such scenarios, OSPF strict-
mode for BFD may be deployed in conjunction with a BFD dampening or mode for BFD may be deployed in conjunction with a BFD dampening or
hold-down mechanism to help avoid frequent adjacency flaps that cause hold-down mechanism to avoid frequent adjacency flaps that cause
routing churn. routing churn.
6. Backward Compatibility 6. Backward Compatibility
An implementation MUST support OSPF adjacency formation and An implementation MUST support OSPF adjacency formation and
operations with a neighbor router that does not advertise the BFD operations with a neighbor router that does not advertise the strict-
strict-mode capability - both when that neighbor router does not mode for BFD capability - both when that neighbor router does not
support BFD and when it does support BFD but not in the strict-mode support BFD and when it does support BFD but not in the strict-mode
of operation as described in this document. Implementations MAY of operation as described in this document. Implementations MAY
provide an option to specifically enable BFD operations only in the provide an option to specifically enable BFD operation only in the
strict-mode. In this case, an OSPF adjacency with a neighbor that strict-mode. In this case, an OSPF adjacency with a neighbor that
does not support BFD strict-mode would not be established does not support strict-mode for BFD would not be established
successfully. Implementations MAY provide an option to disable BFD successfully. Implementations MAY provide an option to disable
strict-mode which results in the router not advertising the B-bit and strict-mode for BFD which results in the router not advertising the
BFD operations being performed in the same way as prior to this B-bit and BFD operation being performed in the same way as prior to
specification. this specification.
The signaling specified in this document happens at a link-local The signaling specified in this document happens at a link-local
level between routers on that link. A router that does not support level between routers on that link. A router that does not support
this specification would ignore the B-bit in the LLS block of hello this specification would ignore the B-bit in the LLS block of Hello
messages from its neighbors and continue to establish BFD sessions, packets from its neighbors and continue to establish BFD sessions, if
if enabled, without delaying the OSPF adjacency formation. Since the enabled, without delaying the OSPF adjacency formation. Since the
router that does not support this specification would not have set router that does not support this specification would not have set
the B-bit in the LLS block of its own hello messages, its neighbor the B-bit in the LLS block of its own Hello packets, its neighbor
routers that support this specification would not use BFD strict-mode routers that support this specification would not use strict-mode for
with such OSPF routers. As a result, the behavior would be the same BFD with such OSPF routers. As a result, the behavior would be the
as before this specification. Therefore, there are no backward same as before this specification. Therefore, there are no backward
compatibility issues or implementations considerations beyond what is compatibility issues or implementations considerations beyond what is
specified herein. specified herein.
7. IANA Considerations 7. IANA Considerations
This specification updates Link Local Signaling TLV Identifiers This specification updates Link Local Signaling TLV Identifiers
registry. registry.
Following values have been assigned via early allocation: Following values have been assigned via early allocation:
 End of changes. 41 change blocks. 
105 lines changed or deleted 104 lines changed or added

This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/