draft-ietf-mpls-ldp-interarea-03.txt   draft-ietf-mpls-ldp-interarea-04.txt 
Network Working Group B. Decraene Network Working Group B. Decraene
Internet Draft J.L. Le Roux Internet Draft J.L. Le Roux
Document: draft-ietf-mpls-ldp-interarea-03.txt France Telecom Document: draft-ietf-mpls-ldp-interarea-04.txt France Telecom
Intended status: Standards Track Intended status: Standards Track
Expiration Date: August 2008 I. Minei Expiration Date: December 2008 I. Minei
Juniper Networks, Inc. Juniper Networks, Inc.
February 2008
LDP extension for Inter-Area LSP LDP extension for Inter-Area LSP
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
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Abstract Abstract
To facilitate the establishment of Label Switched Paths (LSP) that To facilitate the establishment of Label Switched Paths (LSP) that
would span multiple IGP areas in a given Autonomous System (AS), this would span multiple IGP areas in a given Autonomous System (AS), this
document proposes a new optional label mapping procedure for the document describes a new optional Longest Match Label Mapping
Label Distribution Protocol (LDP). Procedure for the Label Distribution Protocol (LDP).
This procedure allows the use of a label if the Forwarding This procedure allows the use of a label if the Forwarding
Equivalence Class (FEC) Element matches an entry in the routing table Equivalence Class (FEC) Element matches an entry in the routing table
(RIB). Matching is defined by an IP longest match search and does not (RIB). Matching is defined by an IP longest match search and does not
mandate an exact match. mandate an exact match.
Table of Contents Table of Contents
1. Conventions used in this document...........................2 1. Conventions used in this document...........................2
2. Terminology.................................................2 2. Terminology.................................................2
3. Introduction................................................2 3. Introduction................................................2
4. Problem statement...........................................3 4. Problem statement...........................................3
5. Label Mapping Procedure.....................................4 5. Longest Match Label Mapping Message Procedure...............4
6. Application examples........................................5 6. Application examples........................................6
6.1. Inter-area LSPs.............................................5 6.1. Inter-area LSPs.............................................6
6.2. Use of static routes........................................7 6.2. Use of static routes........................................7
7. Caveats for deployment......................................7 7. Caveats for deployment......................................8
7.1. Deployment consideration....................................7 7.1. Deployment considerations...................................8
7.2. Impact on routing convergence time..........................8 7.2. Routing convergence time considerations.....................8
8. Security Considerations.....................................8 8. Security Considerations.....................................9
9. IANA Considerations.........................................8 9. IANA Considerations.........................................9
10. References..................................................9 10. References..................................................9
10.1. Normative References........................................9 10.1. Normative References........................................9
10.2. Informative References......................................9 10.2. Informative References......................................9
11. Acknowledgments.............................................9 11. Acknowledgments............................................10
12. Author's Addresses.........................................10 12. Authors' Addresses.........................................11
1. Conventions used in this document 1. Conventions used in this document
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. document are to be interpreted as described in [RFC 2119].
2. Terminology 2. Terminology
IGP Area: OSPF Area or IS-IS level IGP Area: OSPF Area or IS-IS level
ABR: OSPF Area Border Router or IS-IS L1/L2 router ABR: OSPF Area Border Router or IS-IS L1/L2 router
LSP: Label Switched Path LSP: Label Switched Path
Intra-area LSP: LSP that does not traverse any IGP area boundary. Intra-area LSP: LSP that does not traverse any IGP area boundary.
Inter-area LSP: LSP that traverses at least one IGP area boundary. Inter-area LSP: LSP that traverses at least one IGP area boundary.
3. Introduction 3. Introduction
Link state IGPs such as OSPF [OSPFv2] and IS-IS [IS-IS] allow the Link state Interior Gateway Protocols (IGPs) such as OSPF [OSPFv2]
partition of an autonomous system into areas or levels so as to and IS-IS [IS-IS] allow the partition of an autonomous system into
increase routing scalability within a routing domain. areas or levels so as to increase routing scalability within a
routing domain.
However, [LDP] requires that the IP address of the FEC Element should However, [LDP] recommends that the IP address of the FEC Element
*exactly* match an entry in the IP RIB: according to [LDP] section should *exactly* match an entry in the IP RIB: according to [LDP]
3.5.7.1 (Label Mapping Messages Procedures) "An LSR receiving a Label section 3.5.7.1 (Label Mapping Messages Procedures) "A Label
Mapping message from a downstream LSR for a Prefix SHOULD NOT use the Switching Router (LSR) receiving a Label Mapping message from a
label for forwarding unless its routing table contains an entry that downstream LSR for a Prefix SHOULD NOT use the label for forwarding
exactly matches the FEC Element.". unless its routing table contains an entry that exactly matches the
FEC Element.".
Therefore, MPLS LSPs between LERs in different areas/levels are not Therefore, MPLS LSPs between Label Edge Routers (LERs) in different
setup unless the specific (e.g. /32 for IPv4) loopback addresses of areas/levels are not setup unless the specific (e.g. /32 for IPv4)
all the LERs are redistributed across all areas. loopback addresses of all the LERs are redistributed across all
areas.
The problem statement is discussed in section 4. Then, in section 5 The problem statement is discussed in section 4. Then, in section 5
we extend the Label Mapping Procedure defined in [LDP] so as to we extend the Label Mapping Procedure defined in [LDP] so as to
support the setup of contiguous inter-area LSPs while maintaining IP support the setup of contiguous inter-area LSPs while maintaining IP
prefix aggregation on the ABRs. This basically consists of allowing prefix aggregation on the ABRs. This consists of allowing for longest
for "Longest Match Based" Label Mapping. match based Label Mapping.
4. Problem statement 4. Problem statement
Provider based MPLS VPN networks are expanding with the success of Provider based MPLS (Multi Protocol Label Switching) networks are
Layer 3 VPN ([L3-VPN]) and the new deployments of layer 2 VPNs expanding with the success of Layer 3 VPN (Virtual Private Networks
([VPLS-BGP], [VPLS-LDP]). Service Provider MPLS backbones are [L3-VPN]) and the new deployments of layer 2 VPNs ([VPLS-BGP], [VPLS-
significantly growing both in terms of density with the addition of LDP]). Service providers MPLS backbones are significantly growing
PEs to connect new customers and in terms of footprint as traditional both in terms of density with the addition of Provider Edge (PE)
layer two aggregation networks may be replaced by IP/MPLS networks. routers to connect new customers and in terms of footprint as
traditional layer two aggregation networks may be replaced by IP/MPLS
networks.
As a consequence many providers need to introduce IGP areas. Inter- As a consequence many providers need to introduce IGP areas. Inter-
area LSPs, that is LSPs that traverse at least two IGP areas, are area LSPs, that is LSPs that traverse at least two IGP areas, are
required to ensure MPLS connectivity between PEs located in distinct required to ensure MPLS connectivity between PEs located in distinct
IGP areas. IGP areas.
To set up the required MPLS LSPs between PEs in different IGP areas, To set up the required MPLS LSPs between PEs in different IGP areas,
services providers have currently three solutions: LDP with IGP route service providers have currently three solutions: 1) LDP with IGP
leaking, BGP [MPLS-BGP] over LDP with MPLS hierarchy, or also inter- route leaking, 2) BGP [MPLS-BGP] over LDP with MPLS hierarchy, and 3)
area RSVP-TE [ID-RSVP-TE]. inter-area RSVP-TE (Resource Reservation Protocol-Traffic Engineering
[RSVP-TE]).
IGP route leaking consists in redistributing all specific PE loopback IGP route leaking consists in redistributing all specific PE loopback
addresses across area boundaries. As a result, LDP finds in the RIB addresses across area boundaries. As a result, LDP finds in the
an exact match for its FEC and sets up the LSP. Routing Information Base (RIB) an exact match for its FEC and sets up
As a consequence, the potential benefits that a multi-area domain may the LSP. As a consequence, the potential benefits that a multi-area
yield are significantly diminished since a lot of addresses have to domain may yield are significantly diminished since a lot of
be redistributed by ABRs, and the number of IP entries in the LSDB addresses have to be redistributed by ABRs, and the number of IP
and RIB maintained by every LSR of the domain (whatever the entries in the IGP Link State DataBase (LSDB), RIB and FIB maintained
area/level it belongs to) cannot be minimized. by every LSR of the domain (whatever the area/level it belongs to)
cannot be minimized.
Service providers may also set up these inter-area LSPs by using MPLS Service providers may also set up these inter-area LSPs by using MPLS
hierarchy with BGP [MPLS-BGP] as a label distribution protocol hierarchy with BGP [MPLS-BGP] as a label distribution protocol
between areas. The BGP next hop would typically be the ABRs and the between areas. The BGP next hop would typically be the ABRs and the
BGP-created LSPs would be nested within intra-area LSPs setup by LDP BGP-created LSPs would be nested within intra-area LSPs setup by LDP
between PEs and ABRs and between ABRs. between PEs and ABRs and between ABRs.
This solution is not adequate for Service Providers which don't want This solution is not adequate for service providers which don't want
to run BGP on their P routers as it requires BGP on all ABRs. In to run BGP on their P routers as it requires BGP on all ABRs. In
addition, MPLS hierarchy does not allow locally protecting the LSP addition, MPLS hierarchy does not allow locally protecting the LSP
against ABR failures (IP / LDP Fast Reroute), and hence ensuring sub- against ABR failures (IP / LDP Fast Reroute), and hence ensuring sub-
50ms recovery upon ABR failure. The resulting convergence time may 50ms recovery upon ABR failure. The resulting convergence time may
not be acceptable for stringent SLAs required for voice or mission not be acceptable for stringent Service Level Agreements (SLAs)
critical applications. Finally, this solution requires a significant required for voice or mission critical applications. Finally, this
migration effort for Service Providers which started with LDP and IGP solution requires a significant migration effort for service
route leaking to quickly set-up the fist inter-area LSPs. providers which started with LDP and IGP route leaking to quickly
set-up the first inter-area LSPs.
Service providers may also setup these inter-area LSPs by using Service providers may also setup these inter-area LSPs by using
inter-area RSVP-TE [ID-RSVP-TE]. This is a relevant solution when inter-area RSVP-TE [RSVP-TE]. This is a relevant solution when RSVP-
RSVP-TE is already used for setting up intra-area LSPs, and inter- TE is already used for setting up intra-area LSPs, and inter-area
area traffic engineering features are required. In return this is not traffic engineering features are required. In return this is not a
a desired solution when LDP is already used for setting up intra-area desired solution when LDP is already used for setting up intra-area
LSPs, and inter-area traffic engineering features are not required. LSPs, and inter-area traffic engineering features are not required.
To avoid the above drawbacks, there is a need for an LDP based To avoid the above drawbacks, there is a need for an LDP based
solution which allows setting up contiguous inter-area LSPs while solution which allows setting up contiguous inter-area LSPs while
avoiding leaking of specific PE loopback addresses across area avoiding leaking of specific PE loopback addresses across area
boundaries, and hence keeping all the benefits of IGP hierarchy. boundaries, and hence keeping all the benefits of IGP hierarchy.
In that context, this document defines a new LDP Label Mapping In that context, this document defines a new LDP Label Mapping
Procedure so as to support the setup of contiguous inter-area LSPs Procedure so as to support the setup of contiguous inter-area LSPs
while maintaining IP prefix aggregation on the ABRs. This procedure while maintaining IP prefix aggregation on the ABRs. This procedure
is similar to the one defined in [LDP] but performs a longest match is similar to the one defined in [LDP] but performs an IP longest
when searching the FEC element in the RIB. match when searching the FEC element in the RIB.
5. Label Mapping Procedure 5. Longest Match Label Mapping Message Procedure
This document defines a new label mapping procedure for [LDP]. It is This document defines a new Label Mapping Procedure for [LDP]. It is
applicable to IPv4 and IPv6 prefix FEC elements (addresses families 1 applicable to IPv4 and IPv6 prefix FEC elements (address families 1
and 2 as per [ASSIGNED_AF]). It MUST be possible to activate / and 2 as per [ASSIGNED_AF]). It SHOULD be possible to activate /
deactivate this procedure by configuration and it SHOULD be deactivate this procedure by configuration and it SHOULD be
deactivated by default. It MAY be possible to activate it on a per deactivated by default. It MAY be possible to activate it on a per
prefix basis. prefix basis.
With this new longest match label mapping procedure, a LSR receiving With this new Longest Match Label Mapping Procedure, an LSR receiving
a Label Mapping message from a neighbor LSR for a Prefix Address FEC a Label Mapping message from a neighbor LSR for a Prefix Address FEC
Element (FEC1) SHOULD use the label for MPLS forwarding if its Element FEC1 SHOULD use the label for MPLS forwarding if its routing
routing table contains an entry that matches the FEC Element and the table contains an entry that matches the FEC Element FEC1 and the
advertising LSR is a next hop to reach the FEC. If so, it SHOULD advertising LSR is a next hop to reach FEC1. If so, it SHOULD
advertise the received FEC Element (FEC1) and a label to its LDP advertise the received FEC Element FEC1 and a label to its LDP peers.
peers.
Note that this is the specific FEC (FEC1) that LDP re-advertise to
its peers, and not the aggregated prefix found in the IP RIB during
the longest match search.
By "matching FEC Element", one should understand an IP longest match. By "matching FEC Element", one should understand an IP longest match.
That is, either the LDP FEC element exactly matches an entry in the That is, either the LDP FEC element exactly matches an entry in the
IP RIB or the FEC element is a subset of an IP RIB entry. There is no IP RIB or the FEC element is a subset of an IP RIB entry. There is no
match for other cases such as the FEC element is a superset of a RIB match for other cases such as the FEC element is a superset of a RIB
entry. entry.
Note that LDP re-advertises to its peers the specific FEC element
FEC1, and not the aggregated prefix found in the IP RIB during the
longest match search.
Note that with this longest match Label Mapping Procedure, each LSP Note that with this Longest Match Label Mapping Procedure, each LSP
established by LDP still strictly follows the shortest path(s) established by LDP still strictly follows the shortest path(s)
defined by the IGP. defined by the IGP.
FECs selected by this "Longest Match" label mapping procedure are FECs selected by this Longest Match Label Mapping Procedure are
distributed in an ordered way. In case of LER failure, the removal of distributed in an ordered way. In case of LER failure, the removal of
reachability to the FEC occurs using standard LDP procedures as reachability to the FEC occurs using LDP ordered label distribution
defined in [LDP]. Similarly, the FEC will be removed in an ordered mode procedures. As defined in [LDP] in section A.1.5, the FEC will
way through the propagation of label withdraw messages. The use of be removed in an ordered way through the propagation of Label
this (un)reachability information by application layers using the Withdraw messages. The use of this (un)reachability information by
MPLS LSP (e.g., BGP) is outside the scope of this document. application layers using this MPLS LSP (e.g., [MP-BGP]) is outside
the scope of this document.
As per [LDP], LDP has already some interactions with the RIB. In As per [LDP], LDP has already some interactions with the RIB. In
particular, it needs to be aware of the following events: particular, it needs to be aware of the following events:
- prefix UP when a new IP prefix appears in the RIB - prefix up when a new IP prefix appears in the RIB,
- prefix DOWN when an existing prefix disappears - prefix down when an existing IP prefix disappears,
- next-hop change when an existing prefix have new next hop - next hop change when an existing IP prefix has a new next hop
following a routing change. following a routing change.
With this longest match procedure, multiple FECs may be concerned by With this Longest Match Label Mapping Message Procedure, multiple
a single RIB prefix change. The LSR must check all the FECs which are FECs may be concerned by a single RIB prefix change. The LSR MUST
a subset of this RIB prefix. So some LDP reactions following a RIB check all the FECs which are a subset of this RIB prefix. So some LDP
event are changed: reactions following a RIB event are changed:
- When a new prefix appears in the RIB, the LSR MUST check if this - When a new prefix appears in the RIB, the LSR MUST check if this
prefix is a better match for some existing FECs. E.g. the FEC prefix is a better match for some existing FECs. E.g. the FEC
elements 192.0.2.1/32 and 192.0.2.2/32 used the IP RIB entry elements 192.0.2.1/32 and 192.0.2.2/32 used the IP RIB entry
192.0.0/16 and a new more specific IP RIB entry 192.0.2/24 192.0.2.0/24 and a new more specific IP RIB entry 192.0.2.0/26
appears. This may result in changing the LSR used as next hop appears. This may result in changing the LSR used as next hop
and hence the NHLFE for this FEC. and hence the Next Hop Label Forwarding Entry (NHLFE) for this
FEC.
- When a prefix disappears in the RIB, the LSR MUST check all FEC - When a prefix disappears in the RIB, the LSR MUST check all FEC
elements which are using this RIB prefix as best match. For each elements which are using this RIB prefix as best match. For each
FEC, if another RIB prefix is found as best match, LDP MUST use FEC, if another RIB prefix is found as best match, LDP MUST use
it. This may result in changing the LSR used as next hop and it. This may result in changing the LSR used as next hop and
hence the NHLFE for this FEC. Otherwise, the LSR MUST remove the hence the NHLFE for this FEC. Otherwise, the LSR MUST remove the
FEC binding and send a label withdraw message. FEC binding and send a Label Withdraw message.
- When the next-hop of a RIB prefix change, the LSR must change - When the next hop of a RIB prefix changes, the LSR MUST change
the NHLFE of all the FEC elements using this prefix. the NHLFE of all the FEC elements using this prefix.
Future work may define new management objects to the MPLS LDP MIB
modules [LDP-MIB] to activate/deactivate this Longest Match Label
Mapping Message Procedure, possibly on a per prefix basis.
6. Application examples 6. Application examples
6.1. Inter-area LSPs 6.1. Inter-area LSPs
Consider the following example of an autonomous system with one Consider the following example of an autonomous system with one
backbone area and two edge areas: backbone area and two edge areas:
Area "B" Area "B"
Level 2 / Backbone area Level 2 / Backbone area
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All routers are MPLS enabled and MPLS connectivity (i.e. an LSP) is All routers are MPLS enabled and MPLS connectivity (i.e. an LSP) is
required between all PE routers. required between all PE routers.
In the "egress" area "C", the records available are: In the "egress" area "C", the records available are:
IGP RIB LDP FEC elements: IGP RIB LDP FEC elements:
192.0.2.1/32 192.0.2.1/32 192.0.2.1/32 192.0.2.1/32
192.0.2.2/32 192.0.2.2/32 192.0.2.2/32 192.0.2.2/32
192.0.2.3/32 192.0.2.3/32 192.0.2.3/32 192.0.2.3/32
The area border router ABR1 advertises in the backbone area: The area border router ABR1 advertises in the backbone area:
- the aggregated IP prefix 192.0.2/24 in the IGP - the aggregated IP prefix 192.0.2.0/26 in the IGP
- all the specific IP FEC elements (/32) in LDP - all the specific IP FEC elements (/32) in LDP
In the "backbone" area "B", the records available are: In the "backbone" area "B", the records available are:
IGP RIB LDP FEC elements: IGP RIB LDP FEC elements:
192.0.2/24 192.0.2.1/32 192.0.2.0/26 192.0.2.1/32
192.0.2.2/32 192.0.2.2/32
192.0.2.3/32 192.0.2.3/32
The area border router ABR2 advertises in the area "A": The area border router ABR2 advertises in the area "A":
- an aggregated IP prefix 192.0/16 in the IGP - an aggregated IP prefix 192.0.2.0/24 in the IGP
- all the individual IP FEC elements (/32) in LDP - all the individual IP FEC elements (/32) in LDP
In the "ingress" area "A", the records available are: In the "ingress" area "A", the records available are:
IGP RIB LDP FEC elements: IGP RIB LDP FEC elements:
192.0/16 192.0.2.1/32 192.0.2.0/24 192.0.2.1/32
192.0.2.2/32 192.0.2.2/32
192.0.2.3/32 192.0.2.3/32
In this situation, one LSP is established between the ingress PE4 and In this situation, one LSP is established between the ingress PE4 and
every egress PE of area C while maintaining IP prefix aggregation on every egress PE of area C while maintaining IP prefix aggregation on
the ASBRs. the ASBRs.
6.2. Use of static routes 6.2. Use of static routes
Consider the following example where a LER is dual-connected to two Consider the following example where a LER is dual-connected to two
skipping to change at page 7, line 29 skipping to change at page 7, line 39
+--------LSR1---- +--------LSR1----
| | | |
LER | LER |
| | | |
+--------LSR2---- +--------LSR2----
Figure 2: LER dual-connected to two LSRs. Figure 2: LER dual-connected to two LSRs.
In some situations, especially on the edge of the network, it is In some situations, especially on the edge of the network, it is
valid to use static IP routes between the LER and the two LSRs. If valid to use static IP routes between the LER and the two LSRs. If
necessary, the BFD protocol can be used to quickly detect loss of necessary, the BFD protocol ([BFD]) can be used to quickly detect
connectivity. loss of connectivity.
The LDP specification defined in [LDP] would require on the ingress The LDP specification defined in [LDP] would require on the ingress
LER the configuration and the maintenance of one IP route per egress LER the configuration and the maintenance of one IP route per egress
LER and per outgoing interface. LER and per outgoing interface.
The longest match Label Mapping Procedure described in this document The Longest Match Label Mapping Procedure described in this document
only requires one IP route per outgoing interface. only requires one IP route per outgoing interface.
7. Caveats for deployment 7. Caveats for deployment
7.1. Deployment considerations 7.1. Deployment considerations
LSRs compliant with this document are backward compatible with LSRs LSRs compliant with this document are backward compatible with LSRs
that comply with [LDP]. that comply with [LDP].
For the successful establishment of end-to-end MPLS LSPs whose FEC For the successful establishment of end-to-end MPLS LSPs whose FEC
are aggregated in the RIB, this specification must be implemented on are aggregated in the RIB, this specification must be implemented on
all LSRs in all areas where IP aggregation is used. If an LSR on the all LSRs in all areas where IP aggregation is used. If an LSR on the
path does not support this procedure, then the LSP initiated on the path does not support this procedure, then the LSP initiated on the
egress LSR stops at this non compliant LSR. There are no other egress LSR stops at this non compliant LSR. There are no other
adverse effects. adverse effects.
This extension can be deployed incrementally:
- It can be deployed on a per area or routing domain basis and
does not necessarily require an AS wide deployment. For example,
if all specific IP prefixes are leaked in the IGP backbone area
and only stub areas use IP aggregation, LSRs in the backbone
area don't need to be compliant with this document.
- Within each routing area, LSRs can be upgraded independently, at
any time, in any order and without service disruption. During
deployment, if those LSPs are already used, one should only make
sure that ABRs keep advertising the specific IP prefixes in the
IGP until all LSR of this area are successfully upgraded. Then,
the ABRs can advertise the aggregated prefix only and stop
advertising the specific ones.
A service provider currently leaking specific LER's loopback A service provider currently leaking specific LER's loopback
addresses in the IGP and now considering performing IP aggregation on addresses in the IGP and now considering performing IP aggregation on
ABR should be aware that this may result in suboptimal routing as ABR should be aware that this may result in suboptimal routing as
discussed in [RFC 2966]. discussed in [RFC 2966].
This extension does not necessarily require an AS wide deployment but 7.2. Routing convergence time considerations
can be used on a per area basis. For example, if all specific IP
prefixes are leaked in the IGP backbone area and only stub areas use
IP aggregation, LSRs in the backbone area don't need to be compliant
with this document.
7.2. Impact on routing convergence time
IGP convergence is based on two factors: the SPF calculation and IP and MPLS traffic restoration time is based on two factors: the
FIB/LFIB update time. The SPF calculation scales O(N*Log(N)) where N Shortest Path First (SPF) calculation in the control plane and
is the number of Nodes. The FIB/LFIB update scales O(P) where P is Forwarding Information Base (FIB)/Label FIB (LFIB) update time in the
the number of modified prefixes. Currently, with most routers forwarding plane. The SPF calculation scales O(N*Log(N)) where N is
implementations, the FIB/LFIB update is the dominant component [1]. the number of Nodes. The FIB/LFIB update scales O(P) where P is the
number of modified prefixes. Currently, with most routers
implementations, the FIB/LFIB update is the dominant component [1]
and therefore the bottleneck that should be addressed in priority.
The solution documented in this draft reduces the link state database The solution documented in this draft reduces the link state database
size and the number of FIB entries. However, it does not decrease the size in the control plane and the number of FIB entries in the
number of LFIB entries. forwarding plane. As such it solves the scaling of pure IP routers
sharing the IGP with MPLS routers. However, it does not decrease the
In case of failure of the egress LER node, given that the IGP number of LFIB entries so is not sufficient to solve the scaling of
aggregates IP route on ABRs, the routing convergence behavior is MPLS routers. For this, an additional mechanism is required (e.g.
changed compared to [LDP]. As the IGP does not carry specifics introducing some MPLS hierarchy in LDP). This is out of scope of this
prefixes outside of the egress area, the IGP will not propagate the document.
notification of node failure outside of the area. So application
layers using the LSP may, as a local decision, use the availability
of the MPLS LSP -as advertised by LDP- to achieve LER egress fault
notification in addition to application layer fault detection
mechanisms. For some applications (e.g. BGP) this is expected to be
faster. LDP will withdraw the FEC(s) of the egress LER in an ordered
way through the end-to-end propagation of the LDP withdraw message.
Compared to the IGP, this LDP failure notification may be faster or
slower depending on the implementations, the IGP timers used and the
network topology (network diameter). In typical topologies, the
convergence time is expected to be similar or even faster since there
is no need to wait for three consecutive SPF/PRC timers.
For all others failures (links, Ps and ABRs nodes), the failure Compared to [LDP], for all failures except LER failure (i.e. links,
notification and the convergence are unchanged. Ps and ABRs nodes), the failure notification and the convergence is
unchanged. For LER failure, given that the IGP aggregates IP routes
on ABRs and no longer advertise specific prefixes, the control plane
and more specifically the routing convergence behavior of protocols
(e.g. [MP-BGP]) or applications (e.g. [L3-VPN]) may be changed in
case of failure of the egress LER node. For protocols and
applications which need to track egress LER availability, several
solutions can be used, for example:
- Rely on the LDP ordered label distribution control mode - as
defined in [LDP] - to know the availability of the LSP toward the
egress LER. The egress to ingress propagation time of that
unreachability information is expected to be comparable to the IGP
(but this may be implementation dependant).
- Advertise LER reachability in the IGP for the purpose of the
control plane in a way that do not create IP FIB entries in the
forwarding plane.
8. Security Considerations 8. Security Considerations
The longest match Label Mapping procedure described in this document The Longest Match Label Mapping procedure described in this document
does not introduce any change as far as the Security Consideration does not introduce any change as far as the Security Consideration
section of [LDP] is concerned. section of [LDP] is concerned.
9. IANA Considerations 9. IANA Considerations
This document has no actions for IANA. This document has no actions for IANA.
10. References 10. References
10.1. Normative References 10.1. Normative References
[LDP] L. Andersson, I. Minei, B. Thomas, "LDP Specification", [LDP] Andersson, L., Minei, I., Thomas, B., "LDP
RFC 5036, October 2007 Specification", RFC 5036, October 2007
[ASSIGNED_AF] http://www.iana.org/assignments/address-family- [ASSIGNED_AF] http://www.iana.org/assignments/address-family-
numbers numbers
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
10.2. Informative References 10.2. Informative References
[L3-VPN] Rosen, E., Rekhter, Y. ," BGP/MPLS IP Virtual Private [L3-VPN] Rosen, E., Rekhter, Y. ," BGP/MPLS IP Virtual Private
Networks (VPNs) ", RFC 4374, February 2006 Networks (VPNs) ", RFC 4374, February 2006
[MP-BGP] Bates, T., Chandra, R., Katz, D., Rekhter, Y.,
"Multiprotocol Extensions for BGP-4", RFC 4760, January 2007
[MPLS-BGP] Rekhter, Y., Rosen, E., "Carrying Label Information in [MPLS-BGP] Rekhter, Y., Rosen, E., "Carrying Label Information in
[IS-IS] Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and [IS-IS] Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and
Dual Environments", RFC 1195, December 1990 Dual Environments", RFC 1195, December 1990
[VPLS-BGP] Kompella, K., Rekhter, Y., "Virtual Private LAN Service [VPLS-BGP] Kompella, K., Rekhter, Y., "Virtual Private LAN Service
(VPLS) Using BGP for Auto-discovery and Signaling", RFC 4761, (VPLS) Using BGP for Auto-discovery and Signaling", RFC 4761,
January 2007. January 2007.
[VPLS-LDP] Lasserre, M., Kompella, V., "Virtual Private LAN Service [VPLS-LDP] Lasserre, M., Kompella, V., "Virtual Private LAN Service
(VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC
4762, January 2007. 4762, January 2007.
[RFC 2966] Li, T., Przygienda, T., Smit, H., "Domain-wide Prefix [RFC 2966] Li, T., Przygienda, T., Smit, H., "Domain-wide Prefix
Distribution with Two-Level IS-IS", RFC 2966, October 2000. Distribution with Two-Level IS-IS", RFC 2966, October 2000.
[ID-RSVP-TE] Farrel, Ayyangar, Vasseur, " Inter domain MPLS and [RSVP-TE] Farrel, Ayyangar, Vasseur, "Inter domain MPLS and GMPLS
GMPLS Traffic Engineering - RSVP-TE extensions", draft-ietf- Traffic Engineering - RSVP-TE extensions", RFC 5151, February
ccamp-inter-domain-rsvp-te, work in progress. 2008.
[LDP-MIB] Cucchiara, J., Sjostrand, H., Luciani, J., "Definitions
of Managed Objects for the Multiprotocol Label Switching
(MPLS), Label Distribution Protocol (LDP)", RFC 3815, June
2004.
[BFD] Katz, D., Ward, D., "Bidirectional Forwarding Detection",
draft-ietf-bfd-base-08.txt, March 2008.
[1] Francois, P., Filsfils, C., and Evans, J. 2005. "Achieving sub- [1] Francois, P., Filsfils, C., and Evans, J. 2005. "Achieving sub-
second IGP convergence in large IP networks". ACM SIGCOMM second IGP convergence in large IP networks". ACM SIGCOMM
11. Acknowledgments 11. Acknowledgments
Authors would like to thank Yakov Rekhter, Stefano Previdi, Vach Authors would like to thank Yakov Rekhter, Stefano Previdi, Vach
Kompella, Bob Thomas, Clarence Filsfils, Kireeti Kompella, Luca Kompella, Bob Thomas, Clarence Filsfils, Kireeti Kompella, Luca
Martini, Sina Mirtorabi, Dave McDysan, Benoit Fondeviole, Gilles Martini, Sina Mirtorabi, Dave McDysan, Benoit Fondeviole, Gilles
Bourdon and Christian Jacquenet for the useful discussions on this Bourdon and Christian Jacquenet for the useful discussions on this
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