draft-ietf-mpls-ldp-restart-06.txt   rfc3478.txt 
Network Working Group Manoj Leelanivas (Juniper Networks) Network Working Group M. Leelanivas
Internet Draft Yakov Rekhter(Juniper Networks) Request for Comments: 3478 Y. Rekhter
Expiration Date: April 2003 Rahul Aggarwal (Redback Networks) Category: Standards Track Juniper Networks
R. Aggarwal
Graceful Restart Mechanism for LDP Redback Networks
February 2003
draft-ietf-mpls-ldp-restart-06.txt Graceful Restart Mechanism for Label Distribution Protocol
Status of this Memo Status of this Memo
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all provisions of Section 10 of RFC2026. Internet community, and requests discussion and suggestions for
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Abstract Abstract
This document describes a mechanism that helps to minimize the This document describes a mechanism that helps to minimize the
negative effects on MPLS traffic caused by Label Switching Router's negative effects on MPLS traffic caused by Label Switching Router's
(LSR's) control plane restart, and specifically by the restart of its (LSR's) control plane restart, specifically by the restart of its
Label Distribution Protocol (LDP) component, on LSRs that are capable Label Distribution Protocol (LDP) component, on LSRs that are capable
of preserving the MPLS forwarding component across the restart. of preserving the MPLS forwarding component across the restart.
The mechanism described in this document is applicable to all LSRs, The mechanism described in this document is applicable to all LSRs,
both those with the ability to preserve forwarding state during LDP both those with the ability to preserve forwarding state during LDP
restart and those without (although the latter need to implement only restart and those without (although the latter needs to implement
a subset of the mechanism described in this document). Supporting (a only a subset of the mechanism described in this document).
subset of) the mechanism described here by the LSRs that can not Supporting (a subset of) the mechanism described here by the LSRs
preserve their MPLS forwarding state across the restart would not that can not preserve their MPLS forwarding state across the restart
reduce the negative impact on MPLS traffic caused by their control would not reduce the negative impact on MPLS traffic caused by their
plane restart, but it would minimize the impact if their neighbor(s) control plane restart, but it would minimize the impact if their
are capable of preserving the forwarding state across the restart of neighbor(s) are capable of preserving the forwarding state across the
their control plane and implement the mechanism described here. restart of their control plane and implement the mechanism described
here.
The mechanism makes minimalistic assumptions on what has to be The mechanism makes minimalistic assumptions on what has to be
preserved across restart - the mechanism assumes that only the actual preserved across restart - the mechanism assumes that only the actual
MPLS forwarding state has to be preserved; the mechanism does not MPLS forwarding state has to be preserved; the mechanism does not
require any of the LDP-related state to be preserved across the require any of the LDP-related states to be preserved across the
restart. restart.
The procedures described in this document apply to downstream The procedures described in this document apply to downstream
unsolicited label distribution. Extending these procedures to unsolicited label distribution. Extending these procedures to
downstream on demand label distribution is for further study. downstream on demand label distribution is for further study.
Specification of Requirements Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in BCP 14, RFC 2119
[RFC2119].
Summary for Sub-IP Area
(This section to be removed before publication.)
0.1 Summary
This document describes a mechanism that helps to minimize the
negative effects on MPLS traffic caused by LSR's control plane
restart, and specifically by the restart of its LDP component, on
LSRs that are capable of preserving the MPLS forwarding component
across the restart.
0.2 Related documents
See the Reference Section
0.3 Where does it fit in the Picture of the Sub-IP Work
This work fits squarely in MPLS box.
0.4 Why is it Targeted at this WG
The LDP is a product of the MPLS WG. This document specifies
procedures to minimize the negative effects caused by the restart of
the control plane LDP module. Since the procedures described in this
document are directly related to LDP, it would be logical to target
this document at the MPLS WG.
0.5 Justification
The WG should consider this document, as it allows to minimize the
negative effects caused by the restart of the control plane LDP
module.
1. Motivation 1. Motivation
For the sake of brevity in the context of this document by "the For the sake of brevity in the context of this document, by "the
control plane" we mean "the LDP component of the control plane". control plane" we mean "the LDP component of the control plane".
For the sake of brevity in the context of this document by "MPLS For the sake of brevity in the context of this document, by "MPLS
forwarding state" we mean either <incoming label -> (outgoing label, forwarding state" we mean either <incoming label -> (outgoing label,
next hop)> (non-ingress case), or <FEC->(outgoing label, next hop)> next hop)> (non-ingress case), or <FEC->(outgoing label, next hop)>
(ingress case) mapping. (ingress case) mapping.
In the case where a Label Switching Router (LSR) could preserve its In the case where a Label Switching Router (LSR) could preserve its
MPLS forwarding state across restart of its control plane, and MPLS forwarding state across restart of its control plane,
specifically its LDP component [LDP], it is desirable not to perturb specifically its LDP component [LDP], it is desirable not to perturb
the LSPs going through that LSR (and specifically, the LSPs the LSPs going through that LSR (specifically, the LSPs established
established by LDP). In this document, we describe a mechanism, by LDP). In this document, we describe a mechanism, termed "LDP
termed "LDP Graceful Restart", that allows to accomplish this goal. Graceful Restart", that allows the accomplishment of this goal.
The mechanism described in this document is applicable to all LSRs, The mechanism described in this document is applicable to all LSRs,
both those with the ability to preserve forwarding state during LDP both those with the ability to preserve forwarding state during LDP
restart and those without (although the latter need to implement only restart and those without (although the latter need to implement only
a subset of the mechanism described in this document). Supporting (a a subset of the mechanism described in this document). Supporting (a
subset of) the mechanism described here by the LSRs that can not subset of) the mechanism described here by the LSRs that can not
preserve their MPLS forwarding state across the restart would not preserve their MPLS forwarding state across the restart would not
reduce the negative impact on MPLS traffic caused by their control reduce the negative impact on MPLS traffic caused by their control
plane restart, but it would minimize the impact if their neighbor(s) plane restart, but it would minimize the impact if their neighbor(s)
are capable of preserving the forwarding state across the restart of are capable of preserving the forwarding state across the restart of
their control plane and implement the mechanism described here. their control plane and implement the mechanism described here.
The mechanism makes minimalistic assumptions on what has to be The mechanism makes minimalistic assumptions on what has to be
preserved across restart - the mechanism assumes that only the actual preserved across restart - the mechanism assumes that only the actual
MPLS forwarding state has to be preserved. Clearly this is the MPLS forwarding state has to be preserved. Clearly this is the
minimum amount of state that has to be preserved across the restart minimum amount of state that has to be preserved across the restart
in order not to perturb the LSPs traversing a restarting LSR. The in order not to perturb the LSPs traversing a restarting LSR. The
mechanism does not require any of the LDP-related state to be mechanism does not require any of the LDP-related states to be
preserved across the restart. preserved across the restart.
In the scenario where label binding on an LSR is created/maintained In the scenario where label binding on an LSR is created/maintained
not just by the LDP component of the control plane, but by other not just by the LDP component of the control plane, but by other
protocol components as well (e.g., BGP, RSVP-TE), and the LSR protocol components as well (e.g., BGP, RSVP-TE), and the LSR
supports restart of the individual components of the control plane supports restart of the individual components of the control plane
that create/maintain label binding (e.g., restart of LDP, but no that create/maintain label binding (e.g., restart of LDP, but no
restart of BGP), the LSR needs to preserve across the restart the restart of BGP), the LSR needs to preserve across the restart the
information about which protocol has assigned which labels. information about which protocol has assigned which labels.
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sender. While waiting, the receiver SHOULD retain the MPLS sender. While waiting, the receiver SHOULD retain the MPLS
forwarding state for the (already established) LSPs that traverse a forwarding state for the (already established) LSPs that traverse a
link between the sender and the receiver. The FT Reconnect Timeout link between the sender and the receiver. The FT Reconnect Timeout
should be long enough to allow the restart of the control plane of should be long enough to allow the restart of the control plane of
the sender of the TLV, and specifically its LDP component to bring it the sender of the TLV, and specifically its LDP component to bring it
to the state where the sender could exchange LDP messages with its to the state where the sender could exchange LDP messages with its
neighbors. neighbors.
Setting the FT Reconnect Timeout to 0 indicates that the sender of Setting the FT Reconnect Timeout to 0 indicates that the sender of
the TLV will not preserve its forwarding state across the restart, the TLV will not preserve its forwarding state across the restart,
yet the sender supports the procedures defined in Section "Restart of yet the sender supports the procedures, defined in Section 3.3,
LDP communication with a neighbor LSR" of this document, and "Restart of LDP communication with a neighbor LSR" of this document,
therefore could take advantage if its neighbor can preserve its and therefore could take advantage if its neighbor to preserve its
forwarding state across the restart. forwarding state across the restart.
For a restarting LSR the Recovery Time carries the time (in For a restarting LSR, the Recovery Time carries the time (in
milliseconds) the LSR is willing to retain its MPLS forwarding state milliseconds) the LSR is willing to retain its MPLS forwarding state
that it preserved across the restart. The time is from the moment the that it preserved across the restart. The time is from the moment
LSR sends the Initialization message that carries the FT Session TLV the LSR sends the Initialization message that carries the FT Session
after restart. Setting this time to 0 indicates that the MPLS TLV after restart. Setting this time to 0 indicates that the MPLS
forwarding state wasn't preserved across the restart (or even if it forwarding state was not preserved across the restart (or even if it
was preserved, is no longer available). was preserved, is no longer available).
The Recovery Time SHOULD be long enough to allow the neighboring The Recovery Time SHOULD be long enough to allow the neighboring
LSR's to re-sync all the LSP's in a graceful manner, without creating LSR's to re-sync all the LSP's in a graceful manner, without creating
congestion in the LDP control plane. congestion in the LDP control plane.
3. Operations 3. Operations
An LSR that supports functionality described in this document An LSR that supports functionality described in this document
advertises this to its LDP neighbors by carrying the FT Session TLV advertises this to its LDP neighbors by carrying the FT Session TLV
in the LDP Initialization message. in the LDP Initialization message.
This document assumes that in certain situations, as specified in This document assumes that in certain situations, as specified in
section "Egress LSR", in addition to the MPLS forwarding state, an section 3.1.2, "Egress LSR", in addition to the MPLS forwarding
LSR can also preserve its IP forwarding state across the restart. state, an LSR can also preserve its IP forwarding state across the
Procedures for preserving IP forwarding state across the restart are restart. Procedures for preserving an IP forwarding state across the
defined in [OSPF-RESTART], [ISIS-RESTART], and [BGP-RESTART]. restart are defined in [OSPF-RESTART], [ISIS-RESTART], and [BGP-
RESTART].
3.1. Procedures for the restarting LSR 3.1. Procedures for the restarting LSR
After an LSR restarts its control plane, the LSR MUST check whether After an LSR restarts its control plane, the LSR MUST check whether
it was able to preserve its MPLS forwarding state from prior to the it was able to preserve its MPLS forwarding state from prior to the
restart. If no, then the LSR sets the Recovery Time to 0 in the FT restart. If not, then the LSR sets the Recovery Time to 0 in the FT
Session TLV the LSR sends to its neighbors. Session TLV the LSR sends to its neighbors.
If the forwarding state has been preserved, then the LSR starts its If the forwarding state has been preserved, then the LSR starts its
internal timer, called MPLS Forwarding State Holding timer (the value internal timer, called MPLS Forwarding State Holding timer (the value
of that timer SHOULD be configurable), and marks all the MPLS of that timer SHOULD be configurable), and marks all the MPLS
forwarding state entries as "stale". At the expiration of the timer, forwarding state entries as "stale". At the expiration of the timer,
all the entries still marked as stale SHOULD be deleted. The value of all the entries still marked as stale SHOULD be deleted. The value
the Recovery Time advertised in the FT Session TLV is set to the of the Recovery Time advertised in the FT Session TLV is set to the
(current) value of the timer at the point when the Initialization (current) value of the timer at the point in which the Initialization
message carrying the FT Session TLV is sent. message carrying the FT Session TLV is sent.
We say that an LSR is in the process of restarting when the MPLS We say that an LSR is in the process of restarting when the MPLS
Forwarding State Holding timer is not expired. Once the timer Forwarding State Holding timer is not expired. Once the timer
expires, we say that the LSR completed its restart. expires, we say that the LSR completed its restart.
The following procedures apply when an LSR is in the process of The following procedures apply when an LSR is in the process of
restarting. restarting.
3.1.1. Non-egress LSR 3.1.1. Non-egress LSR
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entry is found, the LSR follows the normal LDP procedures. (Note entry is found, the LSR follows the normal LDP procedures. (Note
that this paragraph describes the scenario where the restarting LSR that this paragraph describes the scenario where the restarting LSR
is neither the egress, nor the penultimate hop that uses penultimate is neither the egress, nor the penultimate hop that uses penultimate
hop popping for a particular LSP. Note also that this paragraph hop popping for a particular LSP. Note also that this paragraph
covers the case where the restarting LSR is the ingress.) covers the case where the restarting LSR is the ingress.)
If the label carried in the Mapping message is an Implicit NULL If the label carried in the Mapping message is an Implicit NULL
label, the LSR searches its MPLS forwarding state for an entry that label, the LSR searches its MPLS forwarding state for an entry that
indicates Label pop (means no outgoing label), and the next hop equal indicates Label pop (means no outgoing label), and the next hop equal
to one of the addresses (next hops) received in the Address message to one of the addresses (next hops) received in the Address message
from the peer. If such an entry is found, the LSR no longer marks the from the peer. If such an entry is found, the LSR no longer marks
entry as stale, the LSR associates the incoming label from that entry the entry as stale, the LSR associates the incoming label from that
with the FEC received in the Label Mapping message from the neighbor, entry with the FEC received in the Label Mapping message from the
and advertises (via LDP) <incoming label, FEC> to its neighbors. If neighbor, and advertises (via LDP) <incoming label, FEC> to its
the found entry has no incoming label, or if no entry is found, the neighbors. If the found entry has no incoming label, or if no entry
LSR follows the normal LDP procedures. (Note that this paragraph is found, the LSR follows the normal LDP procedures. (Note that this
describes the scenario where the restarting LSR is a penultimate hop paragraph describes the scenario where the restarting LSR is a
for a particular LSP, and this LSP uses penultimate hop popping.) penultimate hop for a particular LSP, and this LSP uses penultimate
hop popping.)
The description in the above paragraph assumes that the restarting The description in the above paragraph assumes that the restarting
LSR generates the same label for all the LSPs that terminate on the LSR generates the same label for all the LSPs that terminate on the
same LSR (different from the restarting LSR), and for which the same LSR (different from the restarting LSR), and for which the
restarting LSR is a penultimate hop. If this is not the case, and the restarting LSR is a penultimate hop. If this is not the case, and
restarting LSR generates a unique label per each such LSP, then the the restarting LSR generates a unique label per each such LSP, then
LSR needs to preserve across the restart not just <incoming label, the LSR needs to preserve across the restart, not just the <incoming
(outgoing label, next hop)> mapping, but also the FEC associated with label, (outgoing label, next hop)> mapping, but also the FEC
this mapping. In such case the LSR searches its MPLS forwarding state associated with this mapping. In such case, the LSR searches its
for an entry that (a) indicates Label pop (means no outgoing label), MPLS forwarding state for an entry that (a) indicates Label pop
(b) the next hop equal to one of the addresses (next hops) received (means no outgoing label), (b) indicates the next hop equal to one of
in the Address message from the peer, and (c) has the same FEC as the the addresses (next hops) received in the Address message from the
one received in the Label Mapping message. If such an entry is found, peer, and (c) has the same FEC as the one received in the Label
the LSR no longer marks the entry as stale, the LSR associates the Mapping message. If such an entry is found, the LSR no longer marks
incoming label from that entry with the FEC received in the Label the entry as stale, the LSR associates the incoming label from that
Mapping message from the neighbor, and advertises (via LDP) <incoming entry with the FEC received in the Label Mapping message from the
label, FEC> to its neighbors. If the found entry has no incoming neighbor, and advertises (via LDP) <incoming label, FEC> to its
label, or if no entry is found, the LSR follows the normal LDP neighbors. If the found entry has no incoming label, or if no entry
procedures. is found, the LSR follows the normal LDP procedures.
3.1.2. Egress LSR 3.1.2. Egress LSR
If an LSR determines that it is an egress for a particular FEC, the If an LSR determines that it is an egress for a particular FEC, the
LSR is configured to generate a non-NULL label for that FEC, and the LSR is configured to generate a non-NULL label for that FEC, and that
LSR is configured to generate the same (non-NULL) label for all the the LSR is configured to generate the same (non-NULL) label for all
FECs that share the same next hop and for which the LSR is an egress, the FECs that share the same next hop and for which the LSR is an
the LSR searches its MPLS forwarding state for an entry that egress, the LSR searches its MPLS forwarding state for an entry that
indicates Label pop (means no outgoing label), and the next hop equal indicates Label pop (means no outgoing label), and the next hop equal
to the next hop for that FEC. (Determining the next hop for the FEC to the next hop for that FEC. (Determining the next hop for the FEC
depends on the type of the FEC. For example, when the FEC is an IP depends on the type of the FEC. For example, when the FEC is an IP
address prefix, the next hop for that FEC is determined from the IP address prefix, the next hop for that FEC is determined from the IP
forwarding table.) If such an entry is found, the LSR no longer marks forwarding table.) If such an entry is found, the LSR no longer
this entry as stale, the LSR associates the incoming label from that marks this entry as stale, the LSR associates the incoming label from
entry with the FEC, and advertises (via LDP) <incoming label, FEC> to that entry with the FEC, and advertises (via LDP) <incoming label,
its neighbors. If the found entry has no incoming label, or if no FEC> to its neighbors. If the found entry has no incoming label, or
entry is found, the LSR follows the normal LDP procedures. if no entry is found, the LSR follows the normal LDP procedures.
If an LSR determines that it is an egress for a particular FEC, the If an LSR determines that it is an egress for a particular FEC, the
LSR is configured to generate a non-NULL label for that FEC, and the LSR is configured to generate a non-NULL label for that FEC, and that
LSR is configured to generate a unique label for each such FEC, then the LSR is configured to generate a unique label for each such FEC,
the LSR needs to preserve across the restart not just <incoming then the LSR needs to preserve across the restart, not just the
label, (outgoing label, next hop)> mapping, but also the FEC <incoming label, (outgoing label, next hop)> mapping, but also the
associated with this mapping. In such case the LSR would search its FEC associated with this mapping. In such case, the LSR would search
MPLS forwarding state for an entry that indicates Label pop (means no its MPLS forwarding state for an entry that indicates Label pop
outgoing label), and the next hop equal to the next hop for that FEC (means no outgoing label), and the next hop equal to the next hop for
associated with the entry (Determining the next hop for the FEC that FEC associated with the entry (Determining the next hop for the
depends on the type of the FEC. For example, when the FEC is an IP FEC depends on the type of the FEC. For example, when the FEC is an
address prefix, the next hop for that FEC is determined from the IP IP address prefix, the next hop for that FEC is determined from the
forwarding table.) If such an entry is found, the LSR no longer marks IP forwarding table.) If such an entry is found, the LSR no longer
this entry as stale, the LSR associates the incoming label from that marks this entry as stale, the LSR associates the incoming label from
entry with the FEC, and advertises (via LDP) <incoming label, FEC> to that entry with the FEC, and advertises (via LDP) <incoming label,
its neighbors. If the found entry has no incoming label, or if no FEC> to its neighbors. If the found entry has no incoming label, or
entry is found, the LSR follows the normal LDP procedures. if no entry is found, the LSR follows the normal LDP procedures.
If an LSR determines that it is an egress for a particular FEC, and If an LSR determines that it is an egress for a particular FEC, and
the LSR is configured to generate a NULL (either Explicit or the LSR is configured to generate a NULL (either Explicit or
Implicit) label for that FEC, the LSR just advertises (via LDP) such Implicit) label for that FEC, the LSR just advertises (via LDP) such
label (together with the FEC) to its neighbors. label (together with the FEC) to its neighbors.
3.2. Alternative procedures for the restarting LSR 3.2. Alternative procedures for the restarting LSR
In this section we describe an alternative to the procedures In this section we describe an alternative to the procedures
described in Section "Procedures for the restarting LSR". described in Section 3.1, "Procedures for the restarting LSR".
The procedures described in this section assumes that the restarting The procedures described in this section assumes that the restarting
LSR has (at least) as many unallocated as allocated labels. The LSR has (at least) as many unallocated as allocated labels. The
latter form the MPLS forwarding state that the LSR managed to latter form the MPLS forwarding state that the LSR managed to
preserve across the restart. preserve across the restart.
After an LSR restarts its control plane, the LSR MUST check whether After an LSR restarts its control plane, the LSR MUST check whether
it was able to preserve its MPLS forwarding state from prior to the it was able to preserve its MPLS forwarding state from prior to the
restart. If no, then the LSR sets the Recovery Time to 0 in the FT restart. If no, then the LSR sets the Recovery Time to 0 in the FT
Session TLV the LSR sends to its neighbors. Session TLV the LSR sends to its neighbors.
If the forwarding state has been preserved, then the LSR starts its If the forwarding state has been preserved, then the LSR starts its
internal timer, called MPLS Forwarding State Holding timer (the value internal timer, called MPLS Forwarding State Holding timer (the value
of that timer SHOULD be configurable), and marks all the MPLS of that timer SHOULD be configurable), and marks all the MPLS
forwarding state entries as "stale". At the expiration of the timer, forwarding state entries as "stale". At the expiration of the timer,
all the entries still marked as stale SHOULD be deleted. The value of all the entries still marked as stale SHOULD be deleted. The value
the Recovery Time advertised in the FT Session TLV is set to the of the Recovery Time advertised in the FT Session TLV is set to the
(current) value of the timer at the point when the Initialization (current) value of the timer at the point when the Initialization
message carrying the FT Session TLV is sent. message carrying the FT Session TLV is sent.
We say that an LSR is in the process of restarting when the MPLS We say that an LSR is in the process of restarting when the MPLS
Forwarding State Holding timer is not expired. Once the timer Forwarding State Holding timer is not expired. Once the timer
expires, we say that the LSR completed its restart. expires, we say that the LSR completed its restart.
While an LSR is in the process of restarting, the LSR creates local While an LSR is in the process of restarting, the LSR creates local
label binding by following the normal LDP procedures. label binding by following the normal LDP procedures.
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session (rather than discarding the bindings), but marks them as session (rather than discarding the bindings), but marks them as
"stale". "stale".
After detecting that the LDP session with the neighbor went down, the After detecting that the LDP session with the neighbor went down, the
LSR tries to re-establish LDP communication with the neighbor LSR tries to re-establish LDP communication with the neighbor
following the usual LDP procedures. following the usual LDP procedures.
The amount of time the LSR keeps its stale label-FEC bindings is set The amount of time the LSR keeps its stale label-FEC bindings is set
to the lesser of the FT Reconnect Timeout, as was advertised by the to the lesser of the FT Reconnect Timeout, as was advertised by the
neighbor, and a local timer, called the Neighbor Liveness Timer. If neighbor, and a local timer, called the Neighbor Liveness Timer. If
within that time the LSR still doesn't establish an LDP session with within that time the LSR still does not establish an LDP session with
the neighbor, all the stale bindings SHOULD be deleted. The Neighbor the neighbor, all the stale bindings SHOULD be deleted. The Neighbor
Liveness Timer is started when the LSR detects that its LDP session Liveness Timer is started when the LSR detects that its LDP session
with the neighbor went down. The value of the Neighbor Liveness timer with the neighbor went down. The value of the Neighbor Liveness
SHOULD be configurable. timer SHOULD be configurable.
If the LSR re-establishes an LDP session with the neighbor within the If the LSR re-establishes an LDP session with the neighbor within the
lesser of the FT Reconnect Timeout and the Neighbor Liveness Timer, lesser of the FT Reconnect Timeout and the Neighbor Liveness Timer,
and the LSR determines that the neighbor was not able to preserve its and the LSR determines that the neighbor was not able to preserve its
MPLS forwarding state, the LSR SHOULD immediately delete all the MPLS forwarding state, the LSR SHOULD immediately delete all the
stale label-FEC bindings received from that neighbor. If the LSR stale label-FEC bindings received from that neighbor. If the LSR
determines that the neighbor was able to preserve its MPLS forwarding determines that the neighbor was able to preserve its MPLS forwarding
state (as was indicated by the non-zero Recovery Time advertised by state (as was indicated by the non-zero Recovery Time advertised by
the neighbor), the LSR SHOULD further keep the stale label-FEC the neighbor), the LSR SHOULD further keep the stale label-FEC
bindings received from the neighbor for as long as the lesser of the bindings, received from the neighbor, for as long as the lesser of
Recovery Time, advertised by the neighbor, and a local configurable the Recovery Time advertised by the neighbor, and a local
value, called Maximum Recovery Time. configurable value, called Maximum Recovery Time, allows.
The LSR SHOULD try to complete the exchange of its label mapping The LSR SHOULD try to complete the exchange of its label mapping
information with the neighbor within 1/2 of the Recovery Time, as information with the neighbor within 1/2 of the Recovery Time, as
specified in the FT Session TLV received from the neighbor. specified in the FT Session TLV received from the neighbor.
The LSR handles the Label Mapping messages received from the neighbor The LSR handles the Label Mapping messages received from the neighbor
by following the normal LDP procedures, except that (a) it treats the by following the normal LDP procedures, except that (a) it treats the
stale entries in its Label Information Base (LIB), as if these stale entries in its Label Information Base (LIB) as if these entries
entries have been received over the (newly established) session, (b) have been received over the (newly established) session, (b) if the
if the label-FEC binding carried in the message is the same as the label-FEC binding carried in the message is the same as the one that
one that is present in the LIB, but is marked as stale, the LIB entry is present in the LIB, but is marked as stale, the LIB entry is no
no longer is marked as stale, and (c) if for the FEC in the label-FEC longer marked as stale, and (c) if for the FEC in the label-FEC
binding carried in the message there is already a label-FEC binding binding carried in the message there is already a label-FEC binding
in the LIB that is marked as stale, and the label in the LIB binding in the LIB that is marked as stale, and the label in the LIB binding
is different from the label carried in the message, the LSR just is different from the label carried in the message, the LSR just
updates the LIB entry with the new label. updates the LIB entry with the new label.
An LSR, once it creates a <label, FEC> binding, SHOULD keep the value An LSR, once it creates a <label, FEC> binding, SHOULD keep the value
of the label in this binding for as long as the LSR has a route to of the label in this binding for as long as the LSR has a route to
the FEC in the binding. If the route to the FEC disappears, and then the FEC in the binding. If the route to the FEC disappears, and then
re-appears again later, then this may result in using a different re-appears again later, this may result in using a different label
label value, as when the route re-appears, the LSR would create a new value, as when the route re-appears, the LSR would create a new
<label, FEC> binding. <label, FEC> binding.
To minimize the potential mis-routing caused by the label change, To minimize the potential mis-routing caused by the label change when
when creating a new <label, FEC> binding the LSR SHOULD pick up the creating a new <label, FEC> binding, the LSR SHOULD pick up the least
least recently used label. Once an LSR releases a label, the LSR recently used label. Once an LSR releases a label, the LSR SHOULD
SHOULD NOT re-use this label for advertising a <label, FEC> binding NOT re-use this label for advertising a <label, FEC> binding to a
to a neighbor that supports graceful restart for at least the sum of neighbor that supports graceful restart for at least the sum of the
FT Reconnect Timeout plus Recovery Time, as advertised by the FT Reconnect Timeout plus Recovery Time, as advertised by the
neighbor to the LSR. neighbor to the LSR.
4. Security Consideration 4. Security Consideration
The security considerations pertaining to the original LDP protocol The security considerations pertaining to the original LDP protocol
[RFC3036] remain relevant. [RFC3036] remain relevant.
In addition, the mechanism described here renders LSRs that implement In addition, LSRs that implement the mechanism described here are
it to additional denial-of-service attacks as follows: subject to to additional denial-of-service attacks as follows:
An intruder may impersonate an LDP peer in order to force a An intruder may impersonate an LDP peer in order to force a
failure and reconnection of the TCP connection, but where the failure and reconnection of the TCP connection, but where the
intruder sets the Recovery Time to 0 on reconnection. This forces intruder sets the Recovery Time to 0 on reconnection. This forces
all labels received from the peer to be released. all labels received from the peer to be released.
An intruder could intercept the traffic between LDP peers and An intruder could intercept the traffic between LDP peers and
override the setting of the Recovery Time to be set to 0. This override the setting of the Recovery Time to be set to 0. This
forces all labels received from the peer to be released. forces all labels received from the peer to be released.
All of these attacks may be countered by use of an authentication All of these attacks may be countered by use of an authentication
scheme between LDP peers, such as the MD5- based scheme outlined in scheme between LDP peers, such as the MD5- based scheme outlined in
[LDP]. [LDP].
As with LDP, a security issue may exist if an LDP implementation As with LDP, a security issue may exist if an LDP implementation
continues to use labels after expiration of the session that first continues to use labels after expiration of the session that first
caused them to be used. This may arise if the upstream LSR detects caused them to be used. This may arise if the upstream LSR detects
the session failure after the downstream LSR has released and re-used the session failure after the downstream LSR has released and re-used
the label. The problem is most obvious with the platform-wide label the label. The problem is most obvious with the platform-wide label
space and could result in mis-routing of data to other than intended space and could result in mis-routing data to other than intended
destinations and it is conceivable that these behaviors may be destinations, and it is conceivable that these behaviors may be
deliberately exploited to either obtain services without deliberately exploited to either obtain services without
authorization or to deny services to others. authorization or to deny services to others.
In this document, the validity of the session may be extended by the In this document, the validity of the session may be extended by the
Reconnect Timeout, and the session may be re-established in this Reconnect Timeout, and the session may be re-established in this
period. After the expiry of the Reconnection Timeout the session period. After the expiry of the Reconnection Timeout, the session
must be considered to have failed and the same security issue applies must be considered to have failed and the same security issue applies
as described above. as described above.
However, the downstream LSR may declare the session as failed before However, the downstream LSR may declare the session as failed before
the expiration of its Reconnection Timeout. This increases the the expiration of its Reconnection Timeout. This increases the
period during which the downstream LSR might reallocate the label period during which the downstream LSR might reallocate the label
while the upstream LSR continues to transmit data using the old usage while the upstream LSR continues to transmit data using the old usage
of the label. To reduce this issue, this document requires that of the label. To reduce this issue, this document requires that
labels are not re-used until for at least the sum of Reconnect labels not be re-used until at least the sum of Reconnect Timeout
Timeout plus Recovery Time. plus Recovery Time.
5. Intellectual Property Considerations 5. Intellectual Property Considerations
This section is taken from Section 10.4 of [RFC2026]. This section is taken from Section 10.4 of [RFC2026].
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it might or might not be available; neither does it represent that it
skipping to change at page 12, line 5 skipping to change at page 10, line 34
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive this standard. Please address the information to the IETF Executive
Director. Director.
The IETF has been notified of intellectual property rights claimed in The IETF has been notified of intellectual property rights claimed in
regard to some or all of the specification contained in this regard to some or all of the specification contained in this
document. For more information consult the online list of claimed document. For more information consult the online list of claimed
rights. rights.
6. Copyright Notice 6. Acknowledgments
Copyright (C) The Internet Society (date). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implmentation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
7. Acknowledgments
We would like to thank Loa Andersson, Chaitanya Kodeboyina, Ina We would like to thank Loa Andersson, Chaitanya Kodeboyina, Ina
Minei, Nischal Sheth, Enke Chen, and Adrian Farrel for their Minei, Nischal Sheth, Enke Chen, and Adrian Farrel for their
contributions to this document. contributions to this document.
8. Normative References 7. Normative References
[LDP] "Label Distribution Protocol", RFC3036 [LDP] Andersson, L., Doolan, P., Feldman, N., Fredette, A.
and B. Thomas, "Label Distribution Protocol", RFC
3036, January 2001.
[FT-LDP] "Fault Tolerance for LDP and CR-LDP", work in progress [FT-LDP] Farrel, A., "Fault Tolerance for the Label
Distribution Protocol (LDP)", RFC 3479, February 2003.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision [RFC2026] Bradner, S., "The Internet Standards Process --
3", RFC2026 Revision 3", BCP 9, RFC 2026, October 1996.
9. Non-normative References 8. Informative References
[OSPF-RESTART] "Hitless OSPF Restart", draft-ietf-ospf-hitless- [OSPF-RESTART] "Hitless OSPF Restart", Work in Progress.
restart-01.txt
[ISIS-RESTART] "Restart signaling for ISIS", draft-ietf-isis- [ISIS-RESTART] "Restart signaling for ISIS", Work in Progress.
restart-01.txt
[BGP-RESTART] "Graceful Restart Mechanism for BGP", draft-ietf-idr- [BGP-RESTART] "Graceful Restart Mechanism for BGP", Work in
restart-03.txt Progress.
10. Author Information 9. Authors' Addresses
Manoj Leelanivas Manoj Leelanivas
Juniper Networks Juniper Networks
1194 N.Mathilda Ave 1194 N.Mathilda Ave
Sunnyvale, CA 94089 Sunnyvale, CA 94089
e-mail: manoj@juniper.net
EMail: manoj@juniper.net
Yakov Rekhter Yakov Rekhter
Juniper Networks Juniper Networks
1194 N.Mathilda Ave 1194 N.Mathilda Ave
Sunnyvale, CA 94089 Sunnyvale, CA 94089
e-mail: yakov@juniper.net
EMail: yakov@juniper.net
Rahul Aggarwal Rahul Aggarwal
Redback Networks Redback Networks
350 Holger Way 350 Holger Way
San Jose, CA 95134 San Jose, CA 95134
e-mail: rahul@redback.com
EMail: rahul@redback.com
10. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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