Internet DRAFT - draft-atlas-mpls-ldp-mrt
draft-atlas-mpls-ldp-mrt
MPLS Working Group A. Atlas
Internet-Draft K. Tiruveedhula
Intended status: Standards Track C. Bowers
Expires: June 18, 2015 Juniper Networks
J. Tantsura
Ericsson
IJ. Wijnands
Cisco Systems, Inc.
December 15, 2014
LDP Extensions to Support Maximally Redundant Trees
draft-atlas-mpls-ldp-mrt-03
Abstract
This document specifies extensions to the Label Distribution
Protocol(LDP) to support the creation of label-switched paths for
Maximally Redundant Trees (MRT). A prime use of MRTs is for unicast
and multicast IP/LDP Fast-Reroute, which we will refer to as MRT-FRR.
The sole protocol extension to LDP is simply the ability to advertise
an MRT Capability. This document describes that extension and the
associated behavior expected for LSRs and LERs advertising the MRT
Capability.
MRT-FRR uses LDP multi-topology extensions and requires three
different multi-topology IDs to be allocated from the LDP MT-ID
space.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 18, 2015.
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Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Overview of LDP Signaling Extensions for MRT . . . . . . . . 5
4.1. MRT Capability Advertisement . . . . . . . . . . . . . . 5
4.1.1. Interaction of MRT Capability and MT Capability . . . 6
4.1.2. Interaction of LDP MRT Capability with IPv4 and IPv6 6
4.2. Use of the Rainbow MRT MT-ID . . . . . . . . . . . . . . 7
4.3. MRT-Blue and MRT-Red FECs . . . . . . . . . . . . . . . . 7
5. LDP MRT FEC Advertisements . . . . . . . . . . . . . . . . . 7
5.1. MRT-specific behavior . . . . . . . . . . . . . . . . . . 8
5.1.1. ABR behavior and use of the Rainbow FEC . . . . . . . 8
5.1.2. Proxy-node attachment router behavior . . . . . . . . 9
5.2. LDP protocol procedures in the context of MRT label
distribution . . . . . . . . . . . . . . . . . . . . . . 10
5.2.1. LDP peer in RFC5036 . . . . . . . . . . . . . . . . . 10
5.2.2. Next hop in RFC5036 . . . . . . . . . . . . . . . . . 10
5.2.3. Egress LSR in RFC5036 . . . . . . . . . . . . . . . . 11
5.2.4. Use of Rainbow FEC to satisfy label mapping existence
requirements in RFC5036 . . . . . . . . . . . . . . . 12
5.2.5. Validating FECs in routing table . . . . . . . . . . 13
5.2.6. Recognizing new FECs . . . . . . . . . . . . . . . . 13
5.2.7. Not propagating Rainbow FEC label mappings . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
This document describes the LDP signaling extension and associated
behavior necessary to support the architecture that defines how IP/
LDP Fast-Reroute can use MRTs [I-D.ietf-rtgwg-mrt-frr-architecture].
It is necessary to be familiar with the architecture in
[I-D.ietf-rtgwg-mrt-frr-architecture] to understand how and why the
LDP extensions for behavior are needed.
At least one common standardized algorithm (e.g. the MRT Lowpoint
algorithm explained and fully documented in
[I-D.ietf-rtgwg-mrt-frr-algorithm]) is required so that the routers
supporting MRT computation consistently compute the same MRTs. LDP
depends on an IGP for computation of MRTs and alternates. Extensions
to OSPF are defined in [I-D.atlas-ospf-mrt]. Extension to IS-IS are
defined in [I-D.li-isis-mrt].
MRT can also be used to protect multicast traffic (signalled via PIM
or mLDP) using either global protection or local protection
[I-D.atlas-rtgwg-mrt-mc-arch]. An MRT path can be used to provide
node-protection for mLDP traffic via the mechanisms described in
[I-D.wijnands-mpls-mldp-node-protection]; an MRT path can also be
used to provide link protection for mLDP traffic.
For each destination, IP/LDP Fast-Reroute with MRT (MRT-FRR) creates
two alternate destination-based trees separate from the shortest path
forwarding used during stable operation. LDP uses the multi-topology
extensions [RFC7307] to signal Forwarding Equivalency Classes (FECs)
for these two sets of forwarding trees, MRT-Blue and MRT-Red.
In order to create MRT paths and support IP/LDP Fast-Reroute, a new
capability extension is needed for LDP. An LDP implementation
supporting MRT MUST also follow the rules described here for
originating and managing FECs related to MRT, as indicated by their
multi-topology ID. Network reconvergence is described in
[I-D.ietf-rtgwg-mrt-frr-architecture] and the worst-case network
convergence time can be flooded via the extension in Section 7 of
[I-D.atlas-ospf-mrt].
IP/LDP Fast-Reroute using MRTs can provide 100% coverage for link and
node failures in an arbitrary network topology where the failure
doesn't partition the network. It can also be deployed
incrementally; an MRT Island is formed of connected supporting
routers and the MRTs are computed inside that island.
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2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]
3. Terminology
For ease of reading, some of the terminology defined in
[I-D.ietf-rtgwg-mrt-frr-architecture] is repeated here.
Redundant Trees (RT): A pair of trees where the path from any node
X to the root R along the first tree is node-disjoint with the
path from the same node X to the root along the second tree.
These can be computed in 2-connected graphs.
Maximally Redundant Trees (MRT): A pair of trees where the path
from any node X to the root R along the first tree and the path
from the same node X to the root along the second tree share the
minimum number of nodes and the minimum number of links. Each
such shared node is a cut-vertex. Any shared links are cut-links.
Any RT is an MRT but many MRTs are not RTs. The two MRTs are
referred to as MRT-Blue and MRT-Red.
MRT-Red: MRT-Red is used to describe one of the two MRTs; it is
used to described the associated forwarding topology and MT-ID.
Specifically, MRT-Red is the decreasing MRT where links in the
GADAG are taken in the direction from a higher topologically
ordered node to a lower one.
MRT-Blue: MRT-Blue is used to describe one of the two MRTs; it is
used to described the associated forwarding topology and MT-ID.
Specifically, MRT-Blue is the increasing MRT where links in the
GADAG are taken in the direction from a lower topologically
ordered node to a higher one.
Rainbow MRT MT-ID: It is useful to have an MT-ID that refers to the
multiple MRT topologies and to the default topology. This is
referred to as the Rainbow MRT MT-ID and is used by LDP to reduce
signaling and permit the same label to always be advertised to all
peers for the same (MT-ID, Prefix).
MRT Island: From the computing router, the set of routers that
support a particular MRT profile and are connected via MRT-
eligible links.
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Island Border Router (IBR): A router in the MRT Island that is
connected to a router not in the MRT Island and both routers are
in a common area or level.
Island Neighbor (IN): A router that is not in the MRT Island but is
adjacent to an IBR and in the same area/level as the IBR..
4. Overview of LDP Signaling Extensions for MRT
Routers need to know which of their LDP neighbors support MRT. This
is communicated using the MRT Capability Advertisement. Supporting
MRT indicates several different aspects of behavior, as listed below.
1. Sending and receiving multi-topology FEC elements, as defined in
[RFC7307].
2. Understanding the Rainbow MRT MT-ID and applying the associated
labels to all relevant MT-IDs.
3. Advertising the Rainbow MRT FEC to the appropriate neighbors for
the appropriate prefix.
4. If acting as LDP egress for a prefix in the default topology,
also acting as egress for the same prefix in MRT-Red and MRT-
Blue.
5. For a FEC learned from a neighbor that does not support MRT,
originating FECs for MRT-Red and MRT-Blue with the same prefix.
This MRT Island egress behavior is to support an MRT Island that
does not include all routers in the area/level.
4.1. MRT Capability Advertisement
A new MRT Capability Parameter TLV is defined in accordance with LDP
Capability definition guidelines[RFC5561].
The LDP MRT capability can be advertised during LDP session
initialization or after the LDP session is established.
Advertisement of the MRT capability indicates support of the
procedures for establishing the MRT-Blue and MRT-Red LSP paths
detailed in this document. If the peer has not advertised the MRT
capability, then it indicates that LSR does not support MRT
procedures.
If a router advertises the LDP MRT capability to its peer, but the
peer has not advertised the MRT capability, then the router MUST NOT
advertise MRT-related FEC-label bindings to that peer.
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The following is the format of the MRT Capability Parameter.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| MRT Capability (IANA) | Length (= 1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved |
+-+-+-+-+-+-+-+-+
MRT Capability TLV Format
Where:
U-bit: The unknown TLV bit MUST be 1. A router that does not
recognize the MRT Capability TLV will silently ignore the TLV and
process the rest of the message as if the unknown TLV did not
exist.
F-bit: The forward unknown TLV bit MUST be 0 as required by
Section 3 of [RFC5561].
MRT Capability: TBA-MRT-LDP-1 (To Be Allocated by IANA)
Length: The length (in octets) of TLV. Its value is 1.
S-bit: The State bit MUST be 1 if used in LDP "Initialization"
message. MAY be set to 0 or 1 in dynamic "Capability" message to
advertise or withdraw the capability respectively, as described in
[RFC5561].
4.1.1. Interaction of MRT Capability and MT Capability
An LSR advertising the LDP MRT Capability MUST also advertise the LDP
Multi-topology (MT) capability. If an LSR negotiates LDP MRT
Capability with an LDP neighbor without also negotiating the LDP MT
Capability, the LSR MUST behave as if LDP MRT Capability has not been
negotiated and respond with the "MRT Capability negotiated without MT
Capability" status code in the LDP Notification message (defined in
the document). The E-bit of this Notification should be set to 0 to
indicate that this is an Advisory Notification. The LDP session
SHOULD NOT be terminated.
4.1.2. Interaction of LDP MRT Capability with IPv4 and IPv6
The MRT LDP Capability Advertisement does not distinguish between
IPv4 and IPv6 address families. An LSR which advertises the MRT LDP
capability is expected to advertise MRT-related FEC-label bindings
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for the same address families for which it advertises shortest-path
FEC-label bindings. Therefore, an LSR advertising MRT LDP capability
and shortest path FEC-label bindings for IPv4 only (or IPv6 only)
would be expected to advertise MRT-related FEC-label binding for IPv4
only (or IPv6 only). An LSR advertising the MRT LDP capability and
shortest-path FEC label bindings for BOTH IPv4 and IPv6 is expected
to advertise MRT-related FEC-label bindings for BOTH IPv4 and IPv6.
In this scenario, advertising MRT-related FEC-label bindings only for
IPv4 only (or only for IPv6) is not supported.
4.2. Use of the Rainbow MRT MT-ID
Section 10.1 of [I-D.ietf-rtgwg-mrt-frr-architecture] describes the
need for an area border router (ABR) to have different neighbors use
different MPLS labels when sending traffic to the ABR for the same
FEC. More detailed discussion of the Rainbow MRT MT-ID is provided
in Section 5.1.1.
Another use for the Rainbow MRT MT-ID is for an LSR to send the
Rainbow MRT MT-ID with an IMPLICIT_NULL label to indicate
penultimate-hop-popping for all three types of FECs (shortest path,
red, and blue). The EXPLICIT_NULL label advertised using the Rainbow
MRT MT-ID similarly applies to all the types of FECs. Note that the
only scenario in which it is generally useful to advertise the
implicit or explicit null label for all three FEC types is when the
FEC refers to the LSR itself. See Section 5.2.3 for more details.
The value of the Rainbow MRT MT-ID (TBA-MRT-LDP-2) will be assigned
by IANA from the LDP MT-ID space. Prototype experiments have used
the value 3999.
4.3. MRT-Blue and MRT-Red FECs
To provide MRT support in LDP, the MT Prefix FEC is used.
[I-D.ietf-rtgwg-mrt-frr-architecture] contains the IANA request for
the MRT-Red and MRT-Blue MT-IDs associated with the Default MRT
Profile.
The MT Prefix FEC encoding is defined in [RFC7307] and is used
without alteration for advertising label mappings for MRT-Blue, MRT-
Red and Rainbow MRT FECs.
5. LDP MRT FEC Advertisements
This sections describes how and when labels for MRT-Red and MRT-Blue
FECs are advertised. The associated LSPs must be created before a
failure occurs, in order to provide protection paths which are
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immediately usable by the point of local repair in the event of a
failure.
In this section, we will use the term "shortest path FEC" to refer to
the usual FEC associated with the shortest path destination-based
forwarding tree for a given prefix as determined by the IGP. We will
use the terms "red FEC" and "blue FEC" to refer to FECs associated
with the MRT-Red and MRT-Blue destination-based forwarding trees for
a given prefix as determined by a particular MRT algorithm.
We first describe label distribution behavior specific to MRT. Then
we provide the correct interpretation of several important concepts
in [RFC5036] in the context of MRT FEC label distribution.
5.1. MRT-specific behavior
5.1.1. ABR behavior and use of the Rainbow FEC
Section 10.1 of [I-D.ietf-rtgwg-mrt-frr-architecture] describes the
need for an area border router (ABR) to have different neighbors use
different MPLS labels when sending traffic to the ABR for the same
FEC. The method to accomplish this using the Rainbow MRT MT-ID is
described in detail in [I-D.ietf-rtgwg-mrt-frr-architecture]. Here
we provide a brief summary. To those LDP peers in the same area as
the best route to the destination, the ABR advertises two different
labels corresponding to the MRT-Red and MRT-Blue forwarding trees for
the destination. An LDP peer receiving these advertisements forwards
MRT traffic to the ABR using these two different labels, depending on
the FEC of the traffic. We refer to this as best-area advertising
and forwarding behavior, which is identical to normal MRT behavior.
For all other LDP peers supporting MRT, the ABR advertises a FEC-
label binding for the Rainbow MRT MT-ID scoped FEC with the label
corresponding to the default forwarding tree for the destination. An
LDP peer receiving this advertisement forwards MRT traffic to the ABR
using this label, for both MRT Red and MRT Blue traffic. We refer to
this as non-best-area advertising and forwarding behavior.
The use of the Rainbow-FEC by the ABR for non-best-area
advertisements is RECOMMENDED. An ABR MAY advertise the label for
the default topology in separate MRT-Blue and MRT-Red advertisements.
An LSR advertising the MRT capability MUST recognize the Rainbow MRT
MT-ID and associate the advertised label with the specific prefix
with the MRT-Red and MRT-Blue MT-IDs associated with all MRT Profiles
that advertise LDP as the forwarding mechanism.
Due to changes in topology or configuration, an ABR and a given LDP
peer may need to transition from best-area advertising and forwarding
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behavior to non-best-area behavior for a given destination, and vice
versa. When the ABR requires best-area behavior for a red(blue) FEC,
it MUST withdraw any existing label mappings advertisements for the
corresponding rainbow FEC and advertise label mappings for the
red(blue) FEC. When the ABR requires non-best-area behavior for a
red(blue) FEC, it MUST withdraw any existing label mappings for both
red and blue FECs and advertise label mappings for the corresponding
Rainbow FEC label binding.
If an LSR receives a label mapping advertisement for a rainbow FEC
from an MRT LDP peer while it still retains a label mapping for the
corresponding red or blue FEC, the LSR MUST continue to use the label
mapping for the red or blue FEC, and it MUST send a Label Release
Message corresponding to the rainbow FEC label advertisement. If an
LSR receives a label mapping advertisement for red or blue FEC while
it still retains a label mapping for the corresponding rainbow FEC,
the LSR MUST continue to use the label mapping for the rainbow FEC,
and it MUST send a Label Release Message corresponding to the red or
blue FEC label advertisement.
5.1.2. Proxy-node attachment router behavior
Section 11.2 of [I-D.ietf-rtgwg-mrt-frr-architecture] describes how
MRT provides FRR protection for multi-homed prefixes using
calculations involving a named proxy-node. This covers the scenario
where a prefix is originated by a router in the same area as the MRT
Island, but outside of the MRT Island. It also covers the scenario
of a prefix being advertised by a multiple routers in the MRT Island.
In the named proxy-node calculation, each multi-homed prefix is
represented by a conceptual proxy-node which is attached to two real
proxy-node attachment routers. (A single proxy-node attachment
router is allowed in the case of a prefix advertised by a same area
router outside of the MRT Island which is singly connected to the MRT
Island.) All routers in the MRT Island perform the same calculations
to determine the same two proxy-node attachment routers for each
multi-homed prefix. The resulting graph in the computation consists
of the MRT Island with the proxy-node representing the multi-homed
prefix directly attached to the two proxy-node attachment routers.
Conceptually, one then runs the MRT algorithm on this simplified
graph to determine the MRT-red and blue next-hops to reach the proxy-
node, which gives the next-hops to reach the prefix. In this manner,
one can see that one of the two proxy-node attachment routers will
always have a MRT-red next-hop to the proxy-node while the other will
always have the MRT-blue next-hop to the proxy-node. We will refer
to these as the red and blue proxy-node attachment routers
respectively. (In practice, the MRT-red and blue next-hops to reach
the proxy-node can then be determined in a more computationally
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efficient manner based on the MRT-red and blue next-hops to reach the
proxy-node attachment routers, as described in
[I-D.ietf-rtgwg-mrt-frr-algorithm].)
In terms of LDP behavior, a red proxy-node attachment router for a
given prefix MUST originate a label mapping for the red FEC for that
prefix, while the a blue proxy-node attachment router for a given
prefix MUST originate a label mapping for the blue FEC for that
prefix. If the red(blue) proxy-node attachment router is an Island
Border Router (IBR), then when it receives a packet with the label
corresponding to the red(blue) FEC for a prefix, it MUST forward the
packet to the Island Neighbor (IN) whose whose cost was used in the
selection of the IBR as a proxy-node attachment router. The IBR MUST
swap the incoming label for the outgoing label corresponding to the
shortest path FEC for the prefix advertised by the IN. In the case
where the IN does not support LDP, the IBR MUST pop the incoming
label and forward the packet to the IN.
If the proxy-node attachment router is not an IBR, then the packet
MUST be removed from the MRT forwarding topology and sent along the
interface(s) that caused the router to advertise the prefix. This
interface might be out of the area/level/AS.
5.2. LDP protocol procedures in the context of MRT label distribution
[RFC5036] specifies the LDP label distribution procedures for
shortest path FECs. In general, the same procedures can be applied
to the distribution of label mappings for red and blue FECs, provided
that the procedures are interpreted in the context of MRT FEC label
distribution. The correct interpretation of several important
concepts in [RFC5036] in the context of MRT FEC label distribution is
provided below.
5.2.1. LDP peer in RFC5036
In the context of distributing label mappings for red and blue FECs,
we restrict LDP peer in [RFC5036] to mean LDP peers for which the LDP
MRT capability has been negotiated. In order to make this
distinction clear, in this document we will use the term "MRT LDP
peer" to refer to an LDP peer for which the LDP MRT capability has
been negotiated.
5.2.2. Next hop in RFC5036
Several procedures in [RFC5036] use the next hop of a (shortest path)
FEC to determine behavior. The next hop of the shortest path FEC is
based on the shortest path forwarding tree to the prefix associated
with the FEC. When the procedures of [RFC5036] are used to
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distribute label mapping for red and blue FECs, the next hop for the
red/blue FEC is based on the MRT-Red/Blue forwarding tree to the
prefix associated with the FEC.
For example, Appendix A.1.7. of [RFC5036] specifies the response by
an LSR to a change in the next hop for a FEC. For a shortest path
FEC, the next hop may change as the result of the LSR running a
shortest path computation on a modified IGP topology database. For
the red and blue FECs, the red and blue next hops may change as the
result of the LSR running a particular MRT algorithm on a modified
IGP topology database.
As another example, Section 2.6.1.2 of [RFC5036] specifies how that
when an LSR is using LSP Ordered Control, it may initiate the
transmission of a label mapping only for a (shortest path) FEC for
which it has a label mapping for the FEC next hop, or for which the
LSR is the egress. The FEC next hop for a shortest path FEC is based
on the shortest path forwarding tree to the prefix associated with
the FEC. In the context of distributing MRT LDP labels, this
procedure is understood to mean the following. When an LSR is using
LSP Ordered Control, it may initiate the transmission of a label
mapping only for a red(blue) FEC for which it has a label mapping for
the red(blue) FEC next hop, or for which the LSR is the egress. The
red or blue FEC next hop is based on the MRT-Red or Blue forwarding
tree to the prefix associated with the FEC.
5.2.3. Egress LSR in RFC5036
Procedures in [RFC5036] related to Ordered Control label distribution
mode rely on whether or not an LSR may act as an egress LSR for a
particular FEC in order to determine whether or not the LSR may
originate a label mapping for that FEC. The status of being an
egress LSR for a particular FEC is also used in loop detection
procedures in [RFC5036]. Section 2.6.1.2 of [RFC5036] specifies the
conditions under which an LSR may act as an egress LSR with respect
to a particular (shortest path) FEC.
1. The (shortest path) FEC refers to the LSR itself (including one
of its directly attached interfaces).
2. The next hop router for the (shortest path) FEC is outside of the
Label Switching Network.
3. (Shortest path) FEC elements are reachable by crossing a routing
domain boundary.
The conditions for determining an egress LSR with respect to a red or
blue FEC need to be modified. An LSR may act as an egress LSR with
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respect to a particular red(blue) FEC under any of the following
conditions:
1. The prefix associated with the red(blue) FEC refers to the LSR
itself (including one of its directly attached interfaces).
2. The LSR is the red(blue) proxy-node attachment router with
respect to the multi-homed prefix associated with the red(blue)
FEC. This includes the degenerate case of a single red and blue
proxy-node attachment router for a single-homed prefix.
3. The LSR is an area border router (ABR) AND the MRT LDP peer
requires non-best-area advertising and forwarding behavior for
the prefix associated with the FEC.
Note that condition(3) scopes an LSR's status as an egress LSR with
respect to a particular FEC to a particular MRT LDP peer. Therefore,
the condition "Is LSR egress for FEC?" that occurs in several
procedures in [RFC5036] needs to be interpreted as "Is LSR egress for
FEC with respect to Peer?"
Also note that there is no explicit condition that allows an LSR to
be classified as an egress LSR with respect a red or blue FEC based
only on the primary next-hop for the shortest path FEC not supporting
LDP, or not supporting LDP MRT capability. These situations are
covered by the proxy-node attachment router and ABR conditions
(conditions 2 and 3). In particular, an Island Border Router is not
the egress LSR for a red(blue) FEC unless it is also the red(blue)
proxy-node attachment router for that FEC.
Also note that in general a proxy-node attachment router for a given
prefix should not advertise an implicit or explicit null label for
the corresponding red or blue FEC, even though it may be an egress
LSR for the shortest path FEC. In general, the proxy-node attachment
router needs to forward red or blue traffic for that prefix to a
particular loop free island neighbor, which may be different from the
shortest path next-hop. The proxy-node attachment router needs to
receive the red or blue traffic with a non-null label to correctly
forward it.
5.2.4. Use of Rainbow FEC to satisfy label mapping existence
requirements in RFC5036
Several procedures in [RFC5036] require the LSR to determine if it
has previously received and retained a label mapping for a FEC from
the next hop. In the case of an LSR that has received and retained a
label mapping for a Rainbow FEC from an ABR, the label mapping for
the Rainbow FEC satisfies the label mapping existence requirement for
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the corresponding red and blue FECs. Label mapping existence
requirements in the context of MRT LDP label distribution are
modified as: "Has LSR previously received and retained a label
mapping for the red(blue) FEC (or the corresponding Rainbow FEC) from
the red(blue) next hop?"
As an example, this behavior allows an LSR which has received and
retained a label mapping for the Rainbow FEC to advertise label
mappings for the corresponding red and blue FECs when operating in
Ordered Control label distribution mode.
5.2.5. Validating FECs in routing table
In [RFC5036] an LSR uses its routing table to validate prefixes
associated with shortest path FECs. For example, section 3.5.7.1 of
[RFC5036] specifies that "an LSR receiving a Label Mapping message
from a downstream LSR for a Prefix SHOULD NOT use the label for
forwarding unless its routing table contains an entry that exactly
matches the FEC Element." In the context of MRT FECs, a red or blue
FEC element matches a routing table entry if the corresponding
shortest path FEC element matches a routing table entry.
5.2.6. Recognizing new FECs
Section A.1.6 of [RFC5036] describes the response of an LSR to the
"Recognize New FEC" event, which occurs when an LSR learns a new
(shortest path) FEC via the routing table. In the context of MRT
FECs, when MRT LDP capability has been enabled, when an LSR learns a
new shortest path FEC, it should generate "Recognize New FEC" events
for the corresponding red and blue FECs, in addition to the
"Recognize New FEC" event for the shortest path FEC.
5.2.7. Not propagating Rainbow FEC label mappings
A label mapping for the Rainbow FEC should only be originated by an
ABR under the conditions described in Section 5.1.1. A neighbor of
the ABR that receives a label mapping for the Rainbow FEC MUST NOT
propagate a label mapping for that Rainbow FEC.
6. Security Considerations
The labels distributed by the extensions in this document create
additional forwarding paths that do not following shortest path
routes. The transit label swapping operations defining these
alternative forwarding paths are created during normal operations
(before a failure occurs). Therefore, a malicious packet with an
appropriate label injected into the network from a compromised
location would be forwarded to a destinations along a non-shortest
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path. When this technology is deployed, a network security design
should not rely on assumptions about potentially malicious traffic
only following shortest paths.
It should be noted that the creation of non-shortest forwarding paths
is not unique to MRT.
7. IANA Considerations
IANA is requested to allocate a value for the new LDP Capability TLV
(the first free value in the range 0x0500 to 0x05FF) from the LDP
registry "TLV Type Name Space": MRT Capability TLV (TBA-MRT-LDP-1).
Value Description Reference Notes / Reg. Date
------------- ------------------ ------------ -----------------
TBA-MRT-LDP-1 MRT Capability TLV [This draft]
IANA is requested to allocate a value for the new LDP Status Code
(the first free value in the range 0x00000032-0x00000036) from the
LDP registry "Status Code Name Space": "MRT Capability negotiated
without MT Capability" (TBA-MRT-LDP-3).
Value E Description Reference Notes / Reg. Date
------------- - ------------------------- --------- -----------------
TBA-MRT-LDP-3 0 MRT Capability negotiated [This draft]
without MT Capability
IANA is requested to allocate a value from the MPLS Multi-Topology
Identifiers Name Space [RFC7307]: Rainbow MRT MT-ID (TBA-MRT-LDP-2).
Value Purpose Reference
------------- ------------------ ------------
TBA-MRT-LDP-2 Rainbow MRT MT-ID [This draft]
8. Acknowledgements
The authors would like to thank Ross Callon, Loa Andersson, Stewart
Bryant, Mach Chen, and Greg Mirsky for their suggestions.
9. References
9.1. Normative References
[I-D.ietf-rtgwg-mrt-frr-algorithm]
Enyedi, G., Csaszar, A., Atlas, A., Bowers, C., and A.
Gopalan, "Algorithms for computing Maximally Redundant
Trees for IP/LDP Fast-Reroute", draft-rtgwg-mrt-frr-
algorithm-01 (work in progress), July 2014.
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[I-D.ietf-rtgwg-mrt-frr-architecture]
Atlas, A., Kebler, R., Bowers, C., Enyedi, G., Csaszar,
A., Tantsura, J., Konstantynowicz, M., and R. White, "An
Architecture for IP/LDP Fast-Reroute Using Maximally
Redundant Trees", draft-rtgwg-mrt-frr-architecture-04
(work in progress), July 2014.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
Le Roux, "LDP Capabilities", RFC 5561, July 2009.
[RFC7307] Zhao, Q., Raza, K., Zhou, C., Fang, L., Li, L., and D.
King, "LDP Extensions for Multi-Topology", RFC 7307, July
2014.
9.2. Informative References
[I-D.atlas-ospf-mrt]
Atlas, A., Hegde, S., Bowers, C., and J. Tantsura, "OSPF
Extensions to Support Maximally Redundant Trees", draft-
atlas-ospf-mrt-02 (work in progress), July 2014.
[I-D.atlas-rtgwg-mrt-mc-arch]
Atlas, A., Kebler, R., Wijnands, I., Csaszar, A., and G.
Envedi, "An Architecture for Multicast Protection Using
Maximally Redundant Trees", draft-atlas-rtgwg-mrt-mc-
arch-02 (work in progress), July 2013.
[I-D.li-isis-mrt]
Li, Z., Wu, N., Zhao, Q., Atlas, A., Bowers, C., and J.
Tantsura, "Intermediate System to Intermediate System (IS-
IS) Extensions for Maximally Redundant Trees(MRT)", draft-
li-isis-mrt-01 (work in progress), July 2014.
[I-D.wijnands-mpls-mldp-node-protection]
Wijnands, I., Rosen, E., Raza, K., Tantsura, J., Atlas,
A., and Q. Zhao, "mLDP Node Protection", draft-wijnands-
mpls-mldp-node-protection-04 (work in progress), June
2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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Authors' Addresses
Alia Atlas
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
USA
Email: akatlas@juniper.net
Kishore Tiruveedhula
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
USA
Email: kishoret@juniper.net
Chris Bowers
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
USA
Email: cbowers@juniper.net
Jeff Tantsura
Ericsson
300 Holger Way
San Jose, CA 95134
USA
Email: jeff.tantsura@ericsson.com
IJsbrand Wijnands
Cisco Systems, Inc.
Email: ice@cisco.com
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