< draft-ietf-lsvr-bgp-spf-12.txt   draft-ietf-lsvr-bgp-spf-13.txt >
Network Working Group K. Patel Network Working Group K. Patel
Internet-Draft Arrcus, Inc. Internet-Draft Arrcus, Inc.
Intended status: Standards Track A. Lindem Intended status: Standards Track A. Lindem
Expires: July 30, 2021 Cisco Systems Expires: August 26, 2021 Cisco Systems
S. Zandi S. Zandi
LinkedIn LinkedIn
W. Henderickx W. Henderickx
Nokia Nokia
January 26, 2021 February 22, 2021
BGP Link-State Shortest Path First (SPF) Routing BGP Link-State Shortest Path First (SPF) Routing
draft-ietf-lsvr-bgp-spf-12 draft-ietf-lsvr-bgp-spf-13
Abstract Abstract
Many Massively Scaled Data Centers (MSDCs) have converged on Many Massively Scaled Data Centers (MSDCs) have converged on
simplified layer 3 routing. Furthermore, requirements for simplified layer 3 routing. Furthermore, requirements for
operational simplicity have led many of these MSDCs to converge on operational simplicity have led many of these MSDCs to converge on
BGP as their single routing protocol for both their fabric routing BGP as their single routing protocol for both their fabric routing
and their Data Center Interconnect (DCI) routing. This document and their Data Center Interconnect (DCI) routing. This document
describes extensions to BGP to use BGP Link-State distribution and describes extensions to BGP to use BGP Link-State distribution and
the Shortest Path First (SPF) algorithm used by Internal Gateway the Shortest Path First (SPF) algorithm used by Internal Gateway
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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 30, 2021. This Internet-Draft will expire on August 26, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2021 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
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will only need as many sessions and copies of the NLRI as required will only need as many sessions and copies of the NLRI as required
for redundancy (see Section 4). Additionally, a controller could for redundancy (see Section 4). Additionally, a controller could
inject topology that is learned outside the BGP SPF routing domain. inject topology that is learned outside the BGP SPF routing domain.
Given that controllers are already consuming BGP-LS NLRI [RFC7752], Given that controllers are already consuming BGP-LS NLRI [RFC7752],
this functionality can be reused for BGP-LS-SPF NLRI. this functionality can be reused for BGP-LS-SPF NLRI.
Another potential advantage of BGP SPF is that both IPv6 and IPv4 can Another potential advantage of BGP SPF is that both IPv6 and IPv4 can
both be supported using the BGP-LS-SPF SAFI with the same BGP-LS-SPF both be supported using the BGP-LS-SPF SAFI with the same BGP-LS-SPF
NLRIs. In many MSDC fabrics, the IPv4 and IPv6 topologies are NLRIs. In many MSDC fabrics, the IPv4 and IPv6 topologies are
congruent. Although beyond the scope of this document, multi- congruent, refer to Section 5.2.2 and Section 5.2.3. Although beyond
topology extensions could be used to support separate IPv4, IPv6, the scope of this document, multi-topology extensions could be used
unicast, and multicast topologies while sharing the same NLRI. to support separate IPv4, IPv6, unicast, and multicast topologies
while sharing the same NLRI.
Finally, the BGP SPF topology can be used as an underlay for other Finally, the BGP SPF topology can be used as an underlay for other
BGP SAFIs (using the existing model) and realize all the above BGP SAFIs (using the existing model) and realize all the above
advantages. advantages.
1.3. Document Overview 1.3. Document Overview
The document begins with sections defining the precise relationship The document begins with sections defining the precise relationship
that BGP SPF has with both the base BGP protocol [RFC4271] that BGP SPF has with both the base BGP protocol [RFC4271]
(Section 2) and the BGP Link-State (BGP-LS) extensions [RFC7752] (Section 2) and the BGP Link-State (BGP-LS) extensions [RFC7752]
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+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
The SPF algorithm inherits the values from the IGP Algorithm Types The SPF algorithm inherits the values from the IGP Algorithm Types
registry [RFC8665]. Algorithm 0, (Shortest Path Algorithm (SPF) registry [RFC8665]. Algorithm 0, (Shortest Path Algorithm (SPF)
based on link metric, is supported and described in Section 6.3. based on link metric, is supported and described in Section 6.3.
Support for other algorithm types is beyond the scope of this Support for other algorithm types is beyond the scope of this
specification. specification.
When computing the SPF for a given BGP routing domain, only BGP nodes When computing the SPF for a given BGP routing domain, only BGP nodes
advertising the SPF capability TLV with same SPF algorithm will be advertising the SPF capability TLV with same SPF algorithm will be
included in the Shortest Path Tree (SPT). An implementation MAY included in the Shortest Path Tree (SPT) Section 6.3. An
optionally log detection of a BGP node that has either not advertised implementation MAY optionally log detection of a BGP node that has
the SPF capability TLV or is advertising the SPF capability TLV with either not advertised the SPF capability TLV or is advertising the
an algorithm type other than 0. SPF capability TLV with an algorithm type other than 0.
5.2.1.2. BGP-LS-SPF Node NLRI Attribute SPF Status TLV 5.2.1.2. BGP-LS-SPF Node NLRI Attribute SPF Status TLV
A BGP-LS Attribute TLV of the BGP-LS-SPF Node NLRI is defined to A BGP-LS Attribute TLV of the BGP-LS-SPF Node NLRI is defined to
indicate the status of the node with respect to the BGP SPF indicate the status of the node with respect to the BGP SPF
calculation. This will be used to rapidly take a node out of service calculation. This will be used to rapidly take a node out of service
Section 6.5.2 or to indicate the node is not to be used for transit Section 6.5.2 or to indicate the node is not to be used for transit
(i.e., non-local) traffic Section 6.3. If the SPF Status TLV is not (i.e., non-local) traffic Section 6.3. If the SPF Status TLV is not
included with the Node NLRI, the node is considered to be up and is included with the Node NLRI, the node is considered to be up and is
available for transit traffic. The SPF status is acted upon with the available for transit traffic. The SPF status is acted upon with the
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outside the range of defined values SHOULD be processed and announced outside the range of defined values SHOULD be processed and announced
to other BGP speakers. However, a BGP speaker MUST not use the to other BGP speakers. However, a BGP speaker MUST not use the
Status TLV in its SPF computation. An implementation MAY log this Status TLV in its SPF computation. An implementation MAY log this
information for further analysis. information for further analysis.
5.2.3. IPv4/IPv6 Prefix NLRI Usage 5.2.3. IPv4/IPv6 Prefix NLRI Usage
IPv4/IPv6 Prefix NLRI is advertised with a Local Node Descriptor and IPv4/IPv6 Prefix NLRI is advertised with a Local Node Descriptor and
the prefix and length. The Prefix Descriptors field includes the IP the prefix and length. The Prefix Descriptors field includes the IP
Reachability Information TLV (TLV 265) as described in [RFC7752]. Reachability Information TLV (TLV 265) as described in [RFC7752].
The prefix metric attribute TLV (TLV 1155) MUST be advertised. The The Prefix Metric attribute TLV (TLV 1155) MUST be advertised. The
IGP Route Tag TLV (TLV 1153) MAY be advertised. The usage of other IGP Route Tag TLV (TLV 1153) MAY be advertised. The usage of other
attribute TLVs is beyond the scope of this document. For loopback attribute TLVs is beyond the scope of this document. For loopback
prefixes, the metric should be 0. For non-loopback prefixes, the prefixes, the metric should be 0. For non-loopback prefixes, the
setting of the metric is a local matter and beyond the scope of this setting of the metric is a local matter and beyond the scope of this
document. document.
5.2.3.1. BGP-LS-SPF Prefix NLRI Attribute SPF Status TLV 5.2.3.1. BGP-LS-SPF Prefix NLRI Attribute SPF Status TLV
A BGP-LS Attribute TLV to BGP-LS-SPF Prefix NLRI is defined to A BGP-LS Attribute TLV to BGP-LS-SPF Prefix NLRI is defined to
indicate the status of the prefix with respect to the BGP SPF indicate the status of the prefix with respect to the BGP SPF
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preserve the sequence number's strictly increasing property for the preserve the sequence number's strictly increasing property for the
deployed life of the BGP speaker (including cold restarts). One deployed life of the BGP speaker (including cold restarts). One
mechanism for accomplishing this would be to use the high-order 32 mechanism for accomplishing this would be to use the high-order 32
bits of the sequence number as a wrap/boot count that is incremented bits of the sequence number as a wrap/boot count that is incremented
any time the BGP router loses its sequence number state or the low- any time the BGP router loses its sequence number state or the low-
order 32 bits wrap. order 32 bits wrap.
When incrementing the sequence number for each self-originated NLRI, When incrementing the sequence number for each self-originated NLRI,
the sequence number should be treated as an unsigned 64-bit value. the sequence number should be treated as an unsigned 64-bit value.
If the lower-order 32-bit value wraps, the higher-order 32-bit value If the lower-order 32-bit value wraps, the higher-order 32-bit value
should be incremented and saved in non-volatile storage. If by some should be incremented and saved in non-volatile storage. If a BGP-
chance the BGP-LS-SPF speaker is deployed long enough that there is a LS-SPF speaker completely loses its sequence number state (e.g., the
possibility that the 64-bit sequence number may wrap or a BGP-LS-SPF BGP speaker hardware is replaced or experiences a cold-start), the
speaker completely loses its sequence number state (e.g., the BGP BGP NLRI selection rules (see Section 6.1) will insure convergence,
speaker hardware is replaced or experiences a cold-start), the BGP
NLRI selection rules (see Section 6.1) will insure convergence,
albeit not immediately. albeit not immediately.
The Sequence-Number TLV is mandatory for BGP-LS-SPF NLRI. If the The Sequence-Number TLV is mandatory for BGP-LS-SPF NLRI. If the
Sequence-Number TLV is not received then the corresponding Link NLRI Sequence-Number TLV is not received then the corresponding Link NLRI
is considered as malformed and MUST be handled as 'Treat-as- is considered as malformed and MUST be handled as 'Treat-as-
withdraw'. An implementation MAY log an error for further analysis. withdraw'. An implementation MAY log an error for further analysis.
5.3. NEXT_HOP Manipulation 5.3. NEXT_HOP Manipulation
All BGP peers that support SPF extensions would locally compute the All BGP peers that support SPF extensions would locally compute the
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and stale NLRI will be replaced. The adjacent BGP speaker will and stale NLRI will be replaced. The adjacent BGP speaker will
update their NLRI advertisements, hop by hop, until the BGP routing update their NLRI advertisements, hop by hop, until the BGP routing
domain has converged. domain has converged.
The modified SPF Decision Process performs an SPF calculation rooted The modified SPF Decision Process performs an SPF calculation rooted
at the BGP speaker using the metrics from the Link Attribute IGP at the BGP speaker using the metrics from the Link Attribute IGP
Metric TLV (1095) and the Prefix Attribute Prefix Metric TLV (1155) Metric TLV (1095) and the Prefix Attribute Prefix Metric TLV (1155)
[RFC7752]. As a result, any other BGP attributes that would [RFC7752]. As a result, any other BGP attributes that would
influence the BGP decision process defined in [RFC4271] including influence the BGP decision process defined in [RFC4271] including
ORIGIN, MULTI_EXIT_DISC, and LOCAL_PREF attributes are ignored by the ORIGIN, MULTI_EXIT_DISC, and LOCAL_PREF attributes are ignored by the
SPF algorithm. Furthermore, the NEXT_HOP attribute value is SPF algorithm. The NEXT_HOP attribute is discussed in Section 5.3.
preserved but otherwise ignored during the SPF computation for BGP- The AS_PATH and AS4_PATH [RFC6793] attributes are preserved and used
LS-SPF NLRIs. The AS_PATH and AS4_PATH [RFC6793] attributes are for loop detection [RFC4271]. They are ignored during the SPF
preserved and used for loop detection [RFC4271]. They are ignored computation for BGP-LS-SPF NRLIs.
during the SPF computation for BGP-LS-SPF NRLIs.
6.1.1. BGP Self-Originated NLRI 6.1.1. BGP Self-Originated NLRI
Node, Link, or Prefix NLRI with Node Descriptors matching the local Node, Link, or Prefix NLRI with Node Descriptors matching the local
BGP speaker are considered self-originated. When self-originated BGP speaker are considered self-originated. When self-originated
NLRI is received and it doesn't match the local node's NLRI content NLRI is received and it doesn't match the local node's NLRI content
(including sequence number), special processing is required. (including sequence number), special processing is required.
o If a self-originated NLRI is received and the sequence number is o If a self-originated NLRI is received and the sequence number is
more recent (i.e., greater than the local node's sequence number more recent (i.e., greater than the local node's sequence number
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single SPF computation or multiple SPF computations for separate AFs single SPF computation or multiple SPF computations for separate AFs
is an implementation matter. Normally, IPv4 next-hops are calculated is an implementation matter. Normally, IPv4 next-hops are calculated
for IPv4 prefixes and IPv6 next-hops are calculated for IPv6 for IPv4 prefixes and IPv6 next-hops are calculated for IPv6
prefixes. prefixes.
6.3. SPF Calculation based on BGP-LS-SPF NLRI 6.3. SPF Calculation based on BGP-LS-SPF NLRI
This section details the BGP-LS-SPF local routing information base This section details the BGP-LS-SPF local routing information base
(RIB) calculation. The router will use BGP-LS-SPF Node, Link, and (RIB) calculation. The router will use BGP-LS-SPF Node, Link, and
Prefix NLRI to compute routes using the following algorithm. This Prefix NLRI to compute routes using the following algorithm. This
calculation yields the set of routes associated with the BGP-LS calculation yields the set of routes associated with the BGP SPF
domain. A router calculates the shortest-path tree using itself as Routing Domain. A router calculates the shortest-path tree using
the root. Optimizations to the BGP-LS-SPF algorithm are possible but itself as the root. Optimizations to the BGP-LS-SPF algorithm are
MUST yield the same set of routes. The algorithm below supports possible but MUST yield the same set of routes. The algorithm below
Equal Cost Multi-Path (ECMP) routes. Weighted Unequal Cost Multi- supports Equal Cost Multi-Path (ECMP) routes. Weighted Unequal Cost
Path routes are out of scope. The organization of this section owes Multi-Path routes are out of scope. The organization of this section
heavily to section 16 of [RFC2328]. owes heavily to section 16 of [RFC2328].
The following abstract data structures are defined in order to The following abstract data structures are defined in order to
specify the algorithm. specify the algorithm.
o Local Route Information Base (LOC-RIB) - This routing table o Local Route Information Base (LOC-RIB) - This routing table
contains reachability information (i.e., next hops) for all contains reachability information (i.e., next hops) for all
prefixes (both IPv4 and IPv6) as well as BGP-LS-SPF node prefixes (both IPv4 and IPv6) as well as BGP-LS-SPF node
reachability. Implementations may choose to implement this with reachability. Implementations may choose to implement this with
separate RIBs for each address family and/or Prefix versus Node separate RIBs for each address family and/or Prefix versus Node
reachability. It is synonymous with the Loc-RIB specified in reachability. It is synonymous with the Loc-RIB specified in
[RFC4271]. [RFC4271].
o Global Routing Information Base (GLOBAL-RIB) - This is Routing o Global Routing Information Base (GLOBAL-RIB) - This is Routing
Information Base (RIB) containing the current routes that are Information Base (RIB) containing the current routes that are
installed in the router's forwarding plane. This is commonly installed in the router's forwarding plane. This is commonly
referred to in networking parlance as "the RIB". referred to in networking parlance as "the RIB".
o Link State NLRI Database (LSNDB) - Database of BGP-LS-SPF NLRI o Link State NLRI Database (LSNDB) - Database of BGP-LS-SPF NLRI
that facilitates access to all Node, Link, and Prefix NLRI. that facilitates access to all Node, Link, and Prefix NLRI.
o Candidate List (CAN-LIST) - This is a list of candidate Node o Candidate List (CAN-LIST) - This is a list of candidate Node NLRIs
NLRIs. The list is sorted by the cost to reach the Node NLRI with used during the BGP SPF calculation Section 6.3. The list is
the Node NLRI with the lowest reachability cost at the head of the sorted by the cost to reach the Node NLRI with the Node NLRI with
list. This facilitates execution of the Dijkstra algorithm the lowest reachability cost at the head of the list. This
Section 1.1 where the shortest paths between the local node and facilitates execution of the Dijkstra algorithm Section 1.1 where
other nodes in graph area computed. The CAN-LIST is typically the shortest paths between the local node and other nodes in graph
implemented as a heap but other data structures have been used. area computed. The CAN-LIST is typically implemented as a heap
but other data structures have been used.
The algorithm is comprised of the steps below: The algorithm is comprised of the steps below:
1. The current LOC-RIB is invalidated, and the CAN-LIST is 1. The current LOC-RIB is invalidated, and the CAN-LIST is
initialized to empty. The LOC-RIB is rebuilt during the course initialized to empty. The LOC-RIB is rebuilt during the course
of the SPF computation. The existing routing entries are of the SPF computation. The existing routing entries are
preserved for comparison to determine changes that need to be preserved for comparison to determine changes that need to be
made to the GLOBAL-RIB in step 6. made to the GLOBAL-RIB in step 6.
2. The computing router's Node NLRI is updated in the LOC-RIB with a 2. The computing router's Node NLRI is updated in the LOC-RIB with a
cost of 0 and the Node NLRI is also added to the CAN-LIST. The cost of 0 and the Node NLRI is also added to the CAN-LIST. The
next-hop list is set to the internal loopback next-hop. next-hop list is set to the internal loopback next-hop.
3. The Node NLRI with the lowest cost is removed from the candidate 3. The Node NLRI with the lowest cost is removed from the candidate
list for processing. If the BGP-LS Node attribute includes an list for processing. If the BGP-LS Node attribute doesn't
SPF Status TLV (Section 5.2.1.2) indicating the node is include an SPF Capability TLV (Section 5.2.1.1, the Node NLRI is
unreachable, the Node NLRI is ignored and the next lowest cost ignored and the next lowest cost Node NLRI is selected from
Node NLRI is selected from candidate list. The Node candidate list. The If the BGP-LS Node attribute includes an SPF
corresponding to this NLRI will be referred to as the Current- Status TLV (Section 5.2.1.1) indicating the node is unreachable,
Node. If the candidate list is empty, the SPF calculation has the Node NLRI is ignored and the next lowest cost Node NLRI is
completed and the algorithm proceeds to step 6. selected from candidate list. The Node corresponding to this
NLRI will be referred to as the Current-Node. If the candidate
list is empty, the SPF calculation has completed and the
algorithm proceeds to step 6.
4. All the Prefix NLRI with the same Node Identifiers as the 4. All the Prefix NLRI with the same Node Identifiers as the
Current-Node will be considered for installation. The next- Current-Node will be considered for installation. The next-
hop(s) for these Prefix NLRI are inherited from the Current-Node. hop(s) for these Prefix NLRI are inherited from the Current-Node.
The cost for each prefix is the metric advertised in the Prefix The cost for each prefix is the metric advertised in the Prefix
Attribute Prefix Metric TLV (1155) added to the cost to reach the Attribute Prefix Metric TLV (1155) added to the cost to reach the
Current-Node. The following will be done for each Prefix NLRI Current-Node. The following will be done for each Prefix NLRI
(referred to as the Current-Prefix): (referred to as the Current-Prefix):
* If the BGP-LS Prefix attribute includes an SPF Status TLV * If the BGP-LS Prefix attribute includes an SPF Status TLV
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order to ensure the highest priority propagation and optimal order to ensure the highest priority propagation and optimal
convergence. convergence.
An IGP such as OSPF [RFC2328] will stop using the link as soon as the An IGP such as OSPF [RFC2328] will stop using the link as soon as the
Router-LSA for one side of the link is received. With a BGP Router-LSA for one side of the link is received. With a BGP
advertisement, the link would continue to be used until the last copy advertisement, the link would continue to be used until the last copy
of the BGP-LS-SPF Link NLRI is withdrawn. In order to avoid this of the BGP-LS-SPF Link NLRI is withdrawn. In order to avoid this
delay, the originator of the Link NLRI SHOULD advertise a more recent delay, the originator of the Link NLRI SHOULD advertise a more recent
version with an increased Sequence Number TLV for the BGP-LS-SPF Link version with an increased Sequence Number TLV for the BGP-LS-SPF Link
NLRI including the SPF Status TLV (Section 5.2.2.2) indicating the NLRI including the SPF Status TLV (Section 5.2.2.2) indicating the
link is down with respect to BGP SPF. After some configurable period link is down with respect to BGP SPF. The configurable
of time, which is an implementation dependent, e.g., 2-3 seconds, the LinkStatusDownAdvertise timer controls the interval that the BGP-LS-
BGP-LS-SPF Link NLRI can be withdrawn with no consequence. If the LINK NLRI is advertised with SPF Status indicating the link is down
link becomes available in that period, the originator of the BGP-LS- prior to withdrawal. If the link becomes available in that period,
SPF LINK NLRI will simply advertise a more recent version of the BGP- the originator of the BGP-LS-SPF LINK NLRI SHOULD advertise a more
LS-SPF Link NLRI without the SPF Status TLV in the BGP-LS Link recent version of the BGP-LS-SPF Link NLRI without the SPF Status TLV
Attributes. in the BGP-LS Link Attributes. The suggested default value for the
LinkStatusDownAdvertise timer is 2 seconds.
Similarly, when a prefix becomes unreachable, a more recent version Similarly, when a prefix becomes unreachable, a more recent version
of the BGP-LS-SPF Prefix NLRI will be advertised with the SPF Status of the BGP-LS-SPF Prefix NLRI SHOULD be advertised with the SPF
TLV (Section 5.2.3.1) indicating the prefix is unreachable in the Status TLV (Section 5.2.3.1) indicating the prefix is unreachable in
BGP-LS Prefix Attributes and the prefix will be considered the BGP-LS Prefix Attributes and the prefix will be considered
unreachable with respect to BGP SPF. After some configurable period unreachable with respect to BGP SPF. The configurable
of time, which is implementation dependent, e.g., 2-3 seconds, the PrefixStatusDownAdvertise timer controls the interval that the BGP-
BGP-LS-SPF Prefix NLRI can be withdrawn with no consequence. If the LS-Prefix NLRI is advertised with SPF Status indicating the prefix is
prefix becomes reachable in that period, the originator of the BGP- unreachable prior to withdrawal. If the prefix becomes reachable in
LS-SPF Prefix NLRI will simply advertise a more recent version of the that period, the originator of the BGP-LS-SPF Prefix NLRI SHOULD
BGP-LS-SPF Prefix NLRI without the SPF Status TLV in the BGP-LS advertise a more recent version of the BGP-LS-SPF Prefix NLRI without
Prefix Attributes. the SPF Status TLV in the BGP-LS Prefix Attributes. The suggested
default value for the PrefixStatusDownAdvertise timer is 2 seconds.
6.5.2. Node Failure Convergence 6.5.2. Node Failure Convergence
With BGP without graceful restart [RFC4724], all the NLRI advertised With BGP without graceful restart [RFC4724], all the NLRI advertised
by a node are implicitly withdrawn when a session failure is by a node are implicitly withdrawn when a session failure is
detected. If fast failure detection such as BFD is utilized, and the detected. If fast failure detection such as BFD is utilized, and the
node is on the fastest converging path, the most recent versions of node is on the fastest converging path, the most recent versions of
BGP-LS-SPF NLRI may be withdrawn. This will result into an older BGP-LS-SPF NLRI may be withdrawn. This will result into an older
version of the NLRI being used until the new versions arrive and, version of the NLRI being used until the new versions arrive and,
potentially, unnecessary route flaps. Therefore, BGP-LS-SPF NLRI potentially, unnecessary route flaps. For the BGP-LS-SPF SAFI, NLRI
SHOULD always be retained before being implicitly withdrawn for a SHOULD NOT be implicitly withdrawn immediately to prevent such
configurable implementation-dependent interval, e.g., 2-3 seconds. unnecessary route flaps. The configurable
This will not delay convergence since the adjacent nodes will detect NLRIImplicitWithdrawalDelay timer controls the interval that NLRI is
the link failure and advertise a more recent NLRI indicating the link retained prior to implicit withdrawal after a BGP SPF speaker has
is down with respect to BGP SPF (Section 6.5.1) and the BGP SPF transitioned out of Established state. This will not delay
calculation will fail the bi-directional connectivity check convergence since the adjacent nodes will detect the link failure and
Section 6.3. advertise a more recent NLRI indicating the link is down with respect
to BGP SPF (Section 6.5.1) and the BGP SPF calculation will fail the
bi-directional connectivity check Section 6.3. The suggested default
value for the NLRIImplicitWithdrawalDelay timer is 2 seconds.
7. Error Handling 7. Error Handling
This section describes the Error Handling actions, as described in This section describes the Error Handling actions, as described in
[RFC7606], that are specific to SAFI BGP-LS-SPF BGP Update message [RFC7606], that are specific to SAFI BGP-LS-SPF BGP Update message
processing. processing.
7.1. Processing of BGP-LS-SPF TLVs 7.1. Processing of BGP-LS-SPF TLVs
When a BGP speaker receives a BGP Update containing a malformed Node When a BGP speaker receives a BGP Update containing a malformed Node
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