draft-ietf-mpls-bgp-mpls-restart-04.txt   draft-ietf-mpls-bgp-mpls-restart-05.txt 
Network Working Group Yakov Rekhter (Juniper Networks) Network Working Group Yakov Rekhter (Juniper Networks)
Internet Draft Rahul Aggarwal (Juniper Networks) Internet Draft Rahul Aggarwal (Juniper Networks)
Expiration Date: July 2005 Expiration Date: February 2006
Graceful Restart Mechanism for BGP with MPLS Graceful Restart Mechanism for BGP with MPLS
draft-ietf-mpls-bgp-mpls-restart-04.txt draft-ietf-mpls-bgp-mpls-restart-05.txt
Status of this Memo Status of this Memo
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Abstract Abstract
A mechanism for BGP that would help minimize the negative effects on A mechanism for BGP that helps minimize the negative effects on
routing caused by BGP restart is described in "Graceful Restart routing caused by BGP restart has already been developed an is
Mechanism for BGP" (see [1]). This document extends this mechanism to described in a separate document ("Graceful Restart Mechanism for
also minimize the negative effects on MPLS forwarding caused by the BGP"). This document extends this mechanism to also minimize the
Label Switching Router's (LSR's) control plane restart, and negative effects on MPLS forwarding caused by the Label Switching
specifically by the restart of its BGP component when BGP is used to Router's (LSR's) control plane restart, and specifically by the
carry MPLS labels and the LSR is capable of preserving the MPLS restart of its BGP component when BGP is used to carry MPLS labels
forwarding state across the restart. and the LSR is capable of preserving the MPLS forwarding state across
the restart.
The mechanism described in this document is agnostic with respect to The mechanism described in this document is agnostic with respect to
the types of the addresses carried in the BGP Network Layer the types of the addresses carried in the BGP Network Layer
Reachability Information (NLRI) field. As such it works in Reachability Information (NLRI) field. As such it works in
conjunction with any of the address famililies that could be carried conjunction with any of the address famililies that could be carried
in BGP (e.g., IPv4, IPv6, etc...) in BGP (e.g., IPv4, IPv6, etc...)
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 their forwarding state during both those with the ability to preserve their forwarding state during
BGP restart and those without (although the latter need to implement BGP restart and those without (although the latter need to implement
skipping to change at page 3, line 16 skipping to change at page 3, line 5
neighbor(s) are capable of preserving the forwarding state across the neighbor(s) are capable of preserving the forwarding state across the
restart of their control plane and implement the mechanism described restart of their control plane and implement the mechanism described
here. here.
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 RFC 2119 [RFC2119].
1. Motivation 1. Introduction
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)>, or <Forwarding Equivalence Class (FEC) -> (outgoing next hop)>, or <Forwarding Equivalence Class (FEC) -> (outgoing
label, next hop)>, or <incoming label -> label pop, next hop>, or label, next hop)>, or <incoming label -> label pop, next hop>, or
<incoming label, label pop> mapping. In the context of this document <incoming label, label pop> mapping. In the context of this document
the forwarding state that is referred to in [1] means MPLS forwarding the forwarding state that is referred to in [1] means MPLS forwarding
state, as defined above. In the context of this document the term state, as defined above. In the context of this document the term
"next hop" refers to the next hop as advertised in BGP. "next hop" refers to the next hop as advertised in BGP.
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, and
specifically its BGP component, and BGP is used to carry MPLS labels specifically its BGP component, and BGP is used to carry MPLS labels
(e.g., as specified in [RFC3107]), it may be desirable not to perturb (e.g., as specified in [RFC3107]), it may be desirable not to perturb
the LSPs going through that LSR (and specifically, the LSPs the LSPs going through that LSR (and specifically, the LSPs
established by BGP). In this document, we describe a mechanism that established by BGP) after failure of or restart of the BGP component
allows to accomplish this goal. The mechanism described in this of the control plane. In this document, we describe a mechanism that
allows this goal to be accomplished. The mechanism described in this
document works in conjunction with the mechanism specified in [1]. document works in conjunction with the mechanism specified in [1].
The mechanism described in this document places no restrictions on The mechanism described in this document places no restrictions on
the types of addresses (address families) that it can support. the types of addresses (address families) that it can support.
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 BGP both those with the ability to preserve forwarding state during BGP
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. The their control plane and implement the mechanism described here. The
subset includes all the procedures described in this document, except subset includes all the procedures described in this document, except
the procedures in Sections 4.1, 4.2, 4.3, 5, and 6. the procedures in Sections 4.1, 4.2, 4.3 and 5.
2. General requirements 2. General requirements
First of all an LSR MUST implement the Graceful Restart Mechanism for First of all an LSR MUST implement the Graceful Restart Mechanism for
BGP, as specified in [1]. Second, the LSR SHOULD be capable of BGP, as specified in [1]. Second, the LSR SHOULD be capable of
preserving its MPLS forwarding state across the restart of its preserving its MPLS forwarding state across the restart of its
control plane (including the restart of BGP). Third, for the control plane (including the restart of BGP). Third, for the
<Forwarding Equivalence Class (FEC) -> label> bindings distributed <Forwarding Equivalence Class (FEC) -> label> bindings distributed
via BGP the LSR SHOULD be able either (a) to reconstruct the same via BGP the LSR SHOULD be able either (a) to reconstruct the same
bindings as the LSR had prior to the restart (see Section 4), or (b) bindings as the LSR had prior to the restart (see Section 4), or (b)
to create new <FEC -> label> bindings after restart, while temporary to create new <FEC -> label> bindings after restart, while
maintaining MPLS forwarding state corresponds to both the bindings temporarily maintaining MPLS forwarding state corresponding to both
prior to the restart, as well as to the newly created bindings (see the bindings prior to the restart, as well as to the newly created
Section 5). Fourth, as long as the LSR retains the MPLS forwarding bindings (see Section 5). Fourth, as long as the LSR retains the MPLS
state that the LSR preserved across the restart, the labels from that forwarding state that the LSR preserved across the restart, the
state can not be used to create new local label bindings (but could labels from that state can not be used to create new local label
be used to reconstruct the existing bindings, as per procedures in bindings (but could be used to reconstruct the existing bindings, as
Section 4). Finally, for each next hop, if the next hop is reachable per procedures in Section 4). Finally, for each next hop, if the next
via a Label Switched Path (LSP), then the restarting LSR MUST be able hop is reachable via a Label Switched Path (LSP), then the restarting
to preserve the MPLS forwarding state associated with that LSP across LSR MUST be able to preserve the MPLS forwarding state associated
the restart. with that LSP 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 BGP component of the control plane, but by other not just by the BGP component of the control plane, but by other
protocol components as well (e.g., LDP, RSVP-TE), and the LSR protocol components as well (e.g., LDP, 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 BGP, but no that create/maintain label binding (e.g., restart of BGP, but no
restart of LDP) the LSR MUST be able to preserve across the restart restart of LDP) the LSR MUST be able to preserve across the restart
the information about which protocol has assigned which labels. the information about which protocol has assigned which labels.
After the LSR restarts, it MUST follow the procedures as specified in After the LSR restarts, it MUST follow the procedures as specified in
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An LSR that supports the mechanism described in this document An LSR that supports the mechanism described in this document
advertises this to its peer by using the Graceful Restart Capability, advertises this to its peer by using the Graceful Restart Capability,
as specified in [1]. The Subsequent Address Family Identifier (SAFI) as specified in [1]. The Subsequent Address Family Identifier (SAFI)
in the advertised capability MUST indicate that the Network Layer in the advertised capability MUST indicate that the Network Layer
Reachability Information (NLRI) field carries not just addressing Reachability Information (NLRI) field carries not just addressing
Information, but labels as well (see [RFC3107] as an example of where Information, but labels as well (see [RFC3107] as an example of where
NLRI carries labels). NLRI carries labels).
4. Procedures for the restarting LSR 4. Procedures for the restarting LSR
Procedures in this section applies when a restarting LSR is able to Procedures in this section apply when a restarting LSR is able to
reconstruct the same <FEC -> label> bindings as the LSR had prior to reconstruct the same <FEC -> label> bindings as the LSR had prior to
the restart. the restart.
The procedures described in this section are conceptual and do not The procedures described in this section are conceptual and do not
have to be implemented precisely as described here, as long as the have to be implemented precisely as described here, as long as the
implementations support the described functionality and their implementations support the described functionality and their
externally visible behavior is the same. externally visible behavior is the same.
Once the LSR completes its route selection (as specified in Section Once the LSR completes its route selection (as specified in Section
"Procedures for the Restarting Speaker" of [1]), then in addition to "Procedures for the Restarting Speaker" of [1]), then in addition to
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advertising the route to its neighbors. advertising the route to its neighbors.
4.3. Case 3 4.3. Case 3
The following applies when the LSR does not set BGP next hop to self. The following applies when the LSR does not set BGP next hop to self.
In this case the LSR, when advertising its best route for a In this case the LSR, when advertising its best route for a
particular NLRI just uses the label that was received with that particular NLRI just uses the label that was received with that
route. And if the route was received with no label, the LSR route. And if the route was received with no label, the LSR
advertises the route with no label as well. Either way, the LSR does advertises the route with no label as well. Either way, the LSR does
not allocate label for that route. not allocate a label for that route.
5. Alternative procedures for the restarting LSR 5. 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 "Procedures for the restarting LSR".
Procedures in this section apply when a restarting LSR does not Procedures in this section apply when a restarting LSR does not
reconstruct the same <FEC -> label> bindings as the LSR had prior to reconstruct the same <FEC -> label> bindings as the LSR had prior to
the restart, but instead creates new <FEC -> label> bindings after the restart, but instead creates new <FEC -> label> bindings after
restart, while temporary maintaining MPLS forwarding state restart, while temporarily maintaining MPLS forwarding state
corresponding to both the bindings prior to the restart, as well as corresponding to both the bindings prior to the restart, as well as
to the newly created bindings. to the newly created bindings.
The procedures described in this section requires that for the use by The procedures described in this section require that for the use by
BGP graceful restart the LSR SHOULD have (at least) as many BGP graceful restart the LSR SHOULD have (at least) as many
unallocated labels as labels allocated for the <FEC -> label> unallocated labels as labels allocated for the <FEC -> label>
bindings distributed by BGP. The latter forms the MPLS forwarding bindings distributed by BGP. The latter forms the MPLS forwarding
state that the LSR managed to preserve across the restart. The former state that the LSR managed to preserve across the restart. The former
is used for allocating labels after the restart. is used for allocating labels after the restart.
To create (new) local label bindings after the restart the LSR uses To create (new) local label bindings after the restart the LSR uses
unallocated labels (this is pretty much the normal procedure). unallocated labels (this is pretty much the normal procedure).
The LSR SHOULD retain the MPLS forwarding state that the LSR The LSR SHOULD retain the MPLS forwarding state that the LSR
preserved across the restart at least until the LSR sends End-of-RIB preserved across the restart at least until the LSR sends End-of-RIB
marker to all of its neighbors (by that time the LSR already marker to all of its neighbors (by that time the LSR already
completed its route selection process, and also advertised its Adj- completed its route selection process, and also advertised its Adj-
RIB-Out to its neighbors). The LSR MAY retain the forwarding state RIB-Out to its neighbors). The LSR MAY retain the forwarding state
even a bit longer (the amount of extra time MAY be controlled by even a bit longer (the amount of extra time MAY be controlled by
configuration on the LSR), as to allow the neighbors to receive and configuration on the LSR), as to allow the neighbors to receive and
process the routes that have been advertised by the LSR. After that, process the routes that have been advertised by the LSR. After that,
the LSR MAY delete the MPLS forwarding state that it preserved across the LSR SHOULD delete the MPLS forwarding state that it preserved
the restart. across the restart.
Note that while an LSR is in the process of restarting, the LSR may Note that while an LSR is in the process of restarting, the LSR may
have not one, but two local label bindings for a given BGP route - have not one, but two local label bindings for a given BGP route -
one that was retained from prior to restart, and another that was one that was retained from prior to restart, and another that was
created after the restart. Once the LSR completes its restart, the created after the restart. Once the LSR completes its restart, the
former will be deleted. Both of these bindings though would have the former will be deleted. Both of these bindings though would have the
same outgoing label (and the same next hop). same outgoing label (and the same next hop).
6. Procedures for a neighbor of a restarting LSR 6. Procedures for a neighbor of a restarting LSR
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binding for as long as the LSR has a route to the FEC in the binding. 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 re-appears again later, If the route to the FEC disappears, and then re-appears again later,
then this may result in using a different label value, as when the then this may result in using a different label value, as when the
route re-appears, the LSR would create a new <label, FEC> binding. route re-appears, the LSR would create a new <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 creating a new <label, FEC> binding the LSR SHOULD pick up the when creating a new <label, FEC> binding the LSR SHOULD pick up the
least recently used label. Once an LSR releases a label, the LSR least recently used label. Once an LSR releases a label, the LSR
SHALL NOT re-use this label for advertising a <label, FEC> binding to SHALL NOT re-use this label for advertising a <label, FEC> binding to
a neighbor that supports graceful restart for at least the Restart a neighbor that supports graceful restart for at least the Restart
Time, as advertised by the neighbor to the LSR. Time, as advertised by the neighbor to the LSR. This rule SHALL
apply to any label release at any time.
7. Comparison between alternative procedures for the restarting LSR 7. Comparison between alternative procedures for the restarting LSR
Procedures described in Section 4 involve more computational overhead Procedures described in Section 4 involve more computational overhead
on the restarting router relative to the procedures described in on the restarting router relative to the procedures described in
Section 5. Section 5.
Procedures described in Section 5 requires twice as many labels as Procedures described in Section 5 requires twice as many labels as
the procedures described in Section 4. the procedures described in Section 4.
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In principle it is possible for an LSR to use procedures described in In principle it is possible for an LSR to use procedures described in
Section 4 for some AFI/SAFI(s) and procedures described in Section 5 Section 4 for some AFI/SAFI(s) and procedures described in Section 5
for other AFI/SAFI(s). for other AFI/SAFI(s).
8. Security Consideration 8. Security Consideration
The security considerations pertaining to the original BGP protocol The security considerations pertaining to the original BGP protocol
remain relevant. remain relevant.
In addition, the mechanism described here renders LSRs that implement In addition, the mechanism described here renders LSRs that implement
it to additional denial-of-service attacks as follows: it vulnerable to additional denial-of-service attacks as follows:
An intruder may impersonate a BGP peer in order to force a failure An intruder may impersonate a BGP peer in order to force a failure
and reconnection of the TCP connection, but where the intruder and reconnection of the TCP connection, but where the intruder
sets the Forwarding State (F) bit (as defined in [1]) to 0 on sets the Forwarding State (F) bit (as defined in [1]) to 0 on
reconnection. This forces all labels received from the peer to be reconnection. This forces all labels received from the peer to be
released. released.
An intruder could intercept the traffic between BGP peers and An intruder could intercept the traffic between BGP peers and
override the setting of the Forwarding State (F) bit to be set to override the setting of the Forwarding State (F) bit to be set to
0. This forces all labels received from the peer to be released. 0. This forces all labels received from the peer to be released.
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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 Restart Time. This increases the period during the expiration of its Restart Time. This increases the period during
which the downstream LSR might reallocate the label while the which the downstream LSR might reallocate the label while the
upstream LSR continues to transmit data using the old usage of the upstream LSR continues to transmit data using the old usage of the
label. To reduce this issue, this document requires that labels are label. To reduce this issue, this document requires that labels are
not re-used until for at least the Restart Time. not re-used until for at least the Restart Time.
9. Intellectual Property Considerations 9. Intellectual Property Considerations
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 Rights 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; nor does it represent that it has
has made any effort to identify any such rights. Information on the made any independent effort to identify any such rights. Information
IETF's procedures with respect to rights in standards-track and on the procedures with respect to rights in RFC documents can be
standards-related documentation can be found in BCP-11. Copies of found in BCP 78 and BCP 79.
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to Copies of IPR disclosures made to the IETF Secretariat and any
obtain a general license or permission for the use of such assurances of licenses to be made available, or the result of an
proprietary rights by implementors or users of this specification can attempt made to obtain a general license or permission for the use of
be obtained from the IETF Secretariat. such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
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 that may cover technology that may be required to implement
this standard. Please address the information to the IETF Executive this standard. Please address the information to the IETF at ietf-
Director. ipr@ietf.org.
The IETF has been notified of intellectual property rights claimed in
regard to some or all of the specification contained in this
document. For more information consult the online list of claimed
rights.
Juniper Networks, Inc. is seeking patent protection on some or all of
the technology described in this Internet-Draft. If technology in
this document is adopted as a standard, Juniper Networks agrees to
license, on reasonable and non-discriminatory terms, any patent
rights it obtains covering such technology to the extent necessary to
comply with the standard.
Redback Networks, Inc. is seeking patent protection on some of the
technology described in this Internet-Draft. If technology in this
document is adopted as a standard, Redback Networks agrees to
license, on reasonable and non-discriminatory terms, any patent
rights it obtains covering such technology to the extent necessary to
comply with the standard.
10. Copyright Notice 10. Copyright Notice
Copyright (C) The Internet Society (date). All Rights Reserved. Copyright (C) The Internet Society (2005).
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 This document is subject to the rights, licenses and restrictions
revoked by the Internet Society or its successors or assigns. contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein is provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
11. Acknowledgments 11. Acknowledgments
We would like to thank Chaitanya Kodeboyina and Loa Andersson for We would like to thank Chaitanya Kodeboyina and Loa Andersson for
their review and comments. The approach described in Section their review and comments. The approach described in Section
"Alternative procedures for the restarting LSR" is based on the idea "Alternative procedures for the restarting LSR" is based on the idea
suggested by Manoj Leelanivas. suggested by Manoj Leelanivas.
12. Normative References 12. Normative References
[1] "Graceful Restart Mechanism for BGP", draft-ietf-idr- [1] "Graceful Restart Mechanism for BGP", work in progress
restart-01.txt
[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 Requirement Levels", BCP 14, RFC 2119
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option", RFC2385 Signature Option", RFC2385
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", RFC2026 3", RFC2026
 End of changes. 

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