Internet Engineering Task Force Q. Zhao
Internet-Draft Huawei Technology
Intended status: Standards Track L. Fang
Expires: January 9, 2012 C. Zhou
Cisco Systems
L. Li
ChinaMobile
N. So
Verison Business
R. Torvi
Juniper Networks
July 8, 2011
LDP Extension for Multi Topology Support
draft-zhao-mpls-ldp-multi-topology-02.txt
Abstract
Multi-Topology (MT) routing is supported in IP through extension of
IGP protocols, such as OSPF and IS-IS. Each route computed by OSPF
or IS-IS is associated with a specific topology. Label Distribution
Protocol (LDP) is used to distribute labels for FECs advertised by
routing protocols. It is a natural requirement to extend LDP in
order to make LDP be aware of MT and thus take advantage of MT based
routing.
This document describes options to extend the existing MPLS
signalling protocol (LDP) for creating and maintaining Label
Switching Paths (LSPs) in a Multi-Topology enviroment.
Status of this Memo
This Internet-Draft is submitted to IETF 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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
Zhao, et al. Expires January 9, 2012 [Page 1]
Internet-Draft LDP Multi Topology Extension July 2011
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 9, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Zhao, et al. Expires January 9, 2012 [Page 2]
Internet-Draft LDP Multi Topology Extension July 2011
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Application Scenarios . . . . . . . . . . . . . . . . . . . . 5
3.1. Simplified Data-plane . . . . . . . . . . . . . . . . . . 5
3.2. Using MT for p2p Protection . . . . . . . . . . . . . . . 6
3.3. Using MT for mLDP Protection . . . . . . . . . . . . . . . 6
3.4. Service Separation . . . . . . . . . . . . . . . . . . . . 6
3.5. Simplified inter-AS VPN Solution . . . . . . . . . . . . . 6
4. Associating a FEC or group of FECs with MT-ID . . . . . . . . 7
4.1. MT-ID TLV . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. FEC TLV with MT-ID Extenstion . . . . . . . . . . . . . . 8
5. LDP MT Capability Advertisement . . . . . . . . . . . . . . . 9
5.1. Session Initialization . . . . . . . . . . . . . . . . . . 10
5.2. After Session Setup . . . . . . . . . . . . . . . . . . . 11
6. LDP Sessions . . . . . . . . . . . . . . . . . . . . . . . . . 12
7. Reserved MT ID Values . . . . . . . . . . . . . . . . . . . . 12
8. LDP Messages with FEC TLV and MT-ID TLV . . . . . . . . . . . 12
8.1. Label Mapping Message . . . . . . . . . . . . . . . . . . 13
8.2. Label Request Message . . . . . . . . . . . . . . . . . . 14
8.3. Label Abort Request Message . . . . . . . . . . . . . . . 14
8.4. Label Withdraw Message . . . . . . . . . . . . . . . . . . 15
8.5. Label Release Message . . . . . . . . . . . . . . . . . . 16
9. Session Initialization Message with MT Capability . . . . . . 16
10. MPLS Forwarding in MT . . . . . . . . . . . . . . . . . . . . 17
10.1. Use Label for (FEC, MT-ID) Tuple . . . . . . . . . . . . . 17
11. Security Consideration . . . . . . . . . . . . . . . . . . . . 18
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
13. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 18
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
14.1. Normative References . . . . . . . . . . . . . . . . . . . 19
14.2. Informative References . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
Zhao, et al. Expires January 9, 2012 [Page 3]
Internet-Draft LDP Multi Topology Extension July 2011
1. Terminology
Terminology used in this document
MT-ID: A 12 bit value to represent Multi-Topology ID.
Default Topology: A topology that is built using the MT-ID value
0.
MT topology: A topology that is built using the corresponding
MT-ID.
2. Introduction
There are increasing requirements to support multi-topology in MPLS
network. For example, service providers may want to assign different
level of service(s) to different topologies so that the service
separation can be achieved. It is also possible to have an in-band
management network on top of the original MPLS topology, or maintain
separate routing and MPLS domains for isolated multicast or IPv6
islands within the backbone, or force a subset of an address space to
follow a different MPLS topology for the purpose of security, QoS or
simplified management and/or operations.
OSPF and IS-IS use MT-ID (Multi-Topology Identification) to identify
different topologies. For each topology identified by a MT-ID, IGP
computes a separate SPF tree independently to find the best paths to
the IP prefixes associated with this topology.
For FECs that are associated with a specific topology, we propose to
use the same MT-ID of this topology in LDP. Thus the Label Switching
Path (LSP) for a certian FEC may be created and maintained along the
IGP path in this topology.
Maintaining multiple MTs for MPLS network in a backwards-compatible
manner requires several extensions to the label signaling encoding
and processing procedures. When label is associated with a FEC, the
FEC includes both ip address and topology it belongs to.
There are two possible solutions to support MT awared MPLS network
from MPLS forwarding point of view. The first one is to map label to
both ip address and the corresponding topology. The alternative one
is to use label stacks. The upper label maps to the topology, the
lower label maps to the ip address. The first option does not
require change to data plane, and it could use multiple labels for
the same address on different topologies. The second option requires
two lookups on data forwarding plane, and it can use the same label
Zhao, et al. Expires January 9, 2012 [Page 4]
Internet-Draft LDP Multi Topology Extension July 2011
for the same address on different topologies.
There are a few possible ways to apply the MT-ID of a topology in
LDP. One way is to have a new TLV for MT-ID and insert the TLV into
messages describing a FEC that needs Multi-Topology information.
Another approach is to expand the FEC TLV to contain MT-ID if the FEC
needs Multi-Topology information.
MT based MPLS in general can be used for a variety of purposes such
as service separation by assigning each service or a group of
services to a topology, where the managment, QoS and security of the
service or the group of the services can be simplified and
guaranteed, in-band management network "on top" of the original MPLS
topology, maintain separate routing and MPLS forwrding domains for
isolated multicast or IPv6 islands within the backbone, or force a
subset of an address space to follow a different MPLS topology for
the purpose of security, QoS or simplified management and/or
operations.
One of the use of the MT based MPLS is where one class of data
requires low latency links, for example Voice over Internet Protocol
(VoIP) data. As a result such data may be sent preferably via
physical landlines rather than, for example, high latency links such
as satellite links. As a result an additional tolology is defined as
all low latency links on the network and VoIP data packets are
assinged to the additional topology. Another example is security-
critical traffic which may be assigned to an additional topology for
non-radiative links. Further possible examples are file transfer
prtocol (FTP) or SMTP (simple mail transfer protocol) traffic which
can be assigned to additional topology comprising high latency links,
Internet Protocol version 4 (IPv4) versus Internet Protocol version 6
(IPv6) traffic which may be assigned to different topology or data to
be distingushed by the quality of service (QoS) assinged to it.
3. Application Scenarios
3.1. Simplified Data-plane
IGP-MT requires additional data-plane resources maintain multiple
forwarding for each configured MT. On the other hand, MPLS-MT does
not change the data-plane system architecture, if an IGP-MT is mapped
to an MPLS-MT. In case MPLS-MT, incoming label value itself can
determine an MT, and hence it requires a single NHLFE space. MPLS-MT
requires only MT-RIBs in the control-plane, no need to have MT-FIBs.
Forwarding IP packets over a particular MT requires either
configuration or some external means at every node, to maps an
attribute of incoming IP packet header to IGP-MT, which is additional
Zhao, et al. Expires January 9, 2012 [Page 5]
Internet-Draft LDP Multi Topology Extension July 2011
overhead for network management. Whereas, MPLS-MT mapping is
required only at the ingress-PE of an MPLS-MT LSP, because of each
node identifies MPLS-MT LSP switching based on incoming label, hence
no additional configuration is required at every node.
3.2. Using MT for p2p Protection
We know that [IP-FRR-MT] can be used for configuring alternate path
via backup-mt, such that if primary link fails, then backup-MT can be
used for forwarding. However, such techniques require special
marking of IP packets that needs to be forwarded using backup-MT.
MPLS-LDP-MT procedures simplify the forwarding of the MPLS packets
over backup-MT, as MPLS-LDP-MT procedure distribute separate labels
for each MT. How backup paths are computed depends on the
implementation, and the algorithm. The MPLS-LDP-MT in conjunction
with IGP-MT could be used to separate the primary traffic and backup
traffic. For example, service providers can create a backup MT that
consists of links that are meant only for backup traffic. Service
providers can then establish bypass LSPs, standby LSPs, using backup
MT, thus keeping undeterministic backup traffic away from the primary
traffic.
3.3. Using MT for mLDP Protection
Fro the P2mP or MP2MP LSPs setup by using mLDP protocol, there is a
need to setup a backup LSP to have an end to end protection for the
priamry LSP in the appplicaitons such IPTV, where the end to end
protection is a must. Since the mLDP lSp is setup following the IGP
routes, the second LSP setup by following the IGP routes can not be
guranteed to have the link and node diversity from the primary LSP.
By using MPLS-LDP-MT, two topology can be configured with complete
link and node diversity, where the primary and secondary LSP can be
set up independantly within each topology. The two LSPs setup by
this mechanism can protect each other end-to-end.
3.4. Service Separation
MPLS-MT procedures allow establishing two distinct LSPs for the same
FEC, by advertising separate label mapping for each configured
topology. Service providers can implement CoS using MPLS-MT
procedures without requiring to create separate FEC address for each
class. MPLS-MT can also be used separate multicast and unicast
traffic.
3.5. Simplified inter-AS VPN Solution
When the lsp is crossing multiple domains for the inter-as VPN
scenarios, the LSP setup process can be simplified by configuring a
Zhao, et al. Expires January 9, 2012 [Page 6]
Internet-Draft LDP Multi Topology Extension July 2011
set of routers which are in different domains into a new single
domain with a new toplogy ID using the LDP multiple topology. All
the routers belong this new topology will be used to carry the
traffic acrossing multiple domains and since they are in a sinle
domain with the new topology ID, so the LDP lsp set up can be done
easily without the complex inter-as VPN solution's option A, option B
and option C.
4. Associating a FEC or group of FECs with MT-ID
This section describes two approaches to associate a FEC or a group
of FECs to a MT-ID in LDP. One way is to have a new TLV for MT-ID
and insert the MT-ID TLV into messages describing a FEC that needs
Multi-Topology information. Another approach is to extend FEC TLV to
contain the MT-ID if the FEC needs Multi-Topology information.
4.1. MT-ID TLV
The new TLV for MT-ID is defined as below:
Zhao, et al. Expires January 9, 2012 [Page 7]
Internet-Draft LDP Multi Topology Extension July 2011
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| TLV Code Point(TBD) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
U and F bits:
As specified in [RFC3036].
TLV Code Point:
The TLV type which identifies a specific capability.
MT-ID is a 12-bit field containing the ID of the topology
corresponding to the MT-ID used in IGP and LDP. Lack of MT-ID TLV
in messages MUST be interpreted as FECs are used in default
MT-ID (0) only.
A MT-ID TLV can be inserted into the following LDP messages as
an optional parameter.
Label Mapping "Label Mapping Message"
Label Request "Label Request Message"
Label Abort Request "Label Abort Request Message"
Label Withdraw "Label Withdraw Message"
Label Release "Label Release Message"
The message with inserted MT-ID TLV associates a FEC in same message
to the topology identified by MT-ID.
Figure 1: MT-ID TLV Format
4.2. FEC TLV with MT-ID Extenstion
The new TLV for MT-ID is defined as below:
Zhao, et al. Expires January 9, 2012 [Page 8]
Internet-Draft LDP Multi Topology Extension July 2011
The extended FEC TLV has the format below.
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| FEC (TBD) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC Element 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC Element n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This new FEC TLV may contain a number of FEC elements and a MT-ID.
It associates these FEC elements with the topology identified by
the MT-ID. Each FEC TLV can contain only one MT-ID.
Figure 2: Extended FEC with MT-ID
5. LDP MT Capability Advertisement
The LDP MT capability can be advertised either during the LDP session
initailizatin or after the LDP session is setup.
The capability for supporting multi-topology in LDP can be advertised
during LDP session initialization stage by including the LDP MT
capability TLV in LDP Initialization message. After LDP session is
established, the MT capability can also be advertised or changed
using Capability message.
If an LSR has not advertised MT capability, its peer must not send
messages that include MT identifier to this LSR.
If an LSR receives a Label Mapping message with MT parameter from
downstream LSR-D and its upstream LSR-U has not advertised MT
capability, an LSP for the MT will not be established.
If an LSR is changed from non MT capable to MT capable, it sets the S
bit in MT capability TLV and advertises via the Capability message.
The existing LSP is treated as LSP for default MT (ID 0).
Zhao, et al. Expires January 9, 2012 [Page 9]
Internet-Draft LDP Multi Topology Extension July 2011
If an LSR is changed from MT capable to non-MT capable, it may
initiate withdraw of all label mapping for existing LSPs of all non-
default MTs. Alternatively, it may wait until the routing update to
withdraw FEC and release the label mapping for existing LSPs of
specific MT.
There will be case where IGP is MT capable but MPLS is not and the
handling procedure for this case is TBD.
5.1. Session Initialization
In an LDP session initialization, the MT capability may be advertised
through an extended session initailization message. This extended
message has the same format as the original session initialization
message but contains the LDP MT capability TLV as an optional
parameter.
The format of the TLV for LDP MT is specified in the [LDPCAP] as
below:
Zhao, et al. Expires January 9, 2012 [Page 10]
Internet-Draft LDP Multi Topology Extension July 2011
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| TLV Code Point(TBD) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved | |
+-+-+-+-+-+-+-+-+ Capability Data |
| +-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
U and F bits:
As specified in [RFC3036].
TLV Code Point:
The TLV type which identifies a specific capability. The "IANA
Considerations" section of [RFC3036] specifies the assignment of
code points for LDP TLVs.
S-bit:
The State Bit indicates whether the sender is advertising or
withdrawing the capability corresponding to the TLV Code Point.
The State bit is used as follows:
1 - The TLV is advertising the capability specified by the
TLV Code Point.
0 - The TLV is withdrawing the capability specified by the
TLV Code Point.
Capability Data:
Information, if any, about the capability in addition to the TLV
Code Point required to fully specify the capability.
Figure 3: LDP MT CAP TLV
5.2. After Session Setup
During the normal operating stage of LDP sessions, the capability
message defined in the [LDPCAP] will be used with an LDP MT
capability TLV.
The format of the Capability message is as follows:
Zhao, et al. Expires January 9, 2012 [Page 11]
Internet-Draft LDP Multi Topology Extension July 2011
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Capability (IANA) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV_1 (LDP-MT Capability TLV) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV_N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: LDP CAP Format
where TLV_1 (LDP-MT Capability TLV) specifies that the LDP MT
capability is enabled or disbabled by setting the S bit of the TLV to
1 or 0.
6. LDP Sessions
Depending on the number of label spaces supported, if a single gloabl
label space is supported, there will be one session supported for
each pair of peers, even there are multiple topologoies supported
between these two peers. If there are different label spaces
supported for different topologies, which means that label spaces
overlap with each other for different MTs, then it is suggested to
establish multiple sessions for multipple topologies between these
two peers. In this case, multiple LSR-IDs need to be allocated
beforehand so that each multiple topology can have its own label
space ID.
This section is still TBD.
7. Reserved MT ID Values
Certain MT topologies are assigned to serve pre-determined purposes:
[TBD]
8. LDP Messages with FEC TLV and MT-ID TLV
Zhao, et al. Expires January 9, 2012 [Page 12]
Internet-Draft LDP Multi Topology Extension July 2011
8.1. Label Mapping Message
An LSR sends a Label Mapping message to an LDP peer to advertise FEC-
label bindings. In the Optional Parameters' field, the MT-ID TLV
will be inserted.
The encoding for the Label Mapping message is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Mapping (0x0400) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Other Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Optional Parameters
This variable length field contains 0 or more parameters, each
encoded as a TLV. The optional parameters are:
Optional Parameter Length Value
Label Request 4 See below
Message ID TLV
Hop Count TLV 1 See below
Path Vector TLV variable See below
MT TLV variable See below
MT TLV
see the defination section for this new TLV.
Figure 5: Label Mapping Message
Zhao, et al. Expires January 9, 2012 [Page 13]
Internet-Draft LDP Multi Topology Extension July 2011
8.2. Label Request Message
An LSR sends the Label Request message to an LDP peer to request a
binding (mapping) for a FEC. The MT TLV will be inserted into the
Optional parameters' field.
The encoding for the Label Request message is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Request (0x0401) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Label Request Message
In the DU mode, when a label mapping is received by a LSR which has a
downstream with MT capability advertised and an upstream without the
MT capability advertised, it will not send label mapping to its
upstream.
in the DoD mode, the label request is sent down to the downstream LSR
until it finds the downstrream LSR which doesn't support the MT, then
the current LSPR will send a notification to its upstream LSR. In
this case, no LSP is setup.
We propose to add a new notification event to signal the upstream
that the downstream is not capable.
8.3. Label Abort Request Message
The Label Abort Request message may be used to abort an outstanding
Label Request message. The MT TLV may be inserted into the optional
parameters' field.
The encoding for the Label Abort Request message is:
Zhao, et al. Expires January 9, 2012 [Page 14]
Internet-Draft LDP Multi Topology Extension July 2011
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Abort Req (0x0404) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Request Message ID TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Label Abort Request Message
8.4. Label Withdraw Message
An LSR sends a Label Withdraw Message to an LDP peer to signal the
peer that the peer may not continue to use specific FEC-label
mappings the LSR had previously advertised. This breaks the mapping
between the FECs and the labels. The MT TLV will be added into the
optional paramters' field.
The encoding for the Label Withdraw Message is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Withdraw (0x0402) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Label Withdraw Message
Zhao, et al. Expires January 9, 2012 [Page 15]
Internet-Draft LDP Multi Topology Extension July 2011
8.5. Label Release Message
An LSR sends a Label Release message to an LDP peer to signal the
peer that the LSR no longer needs specific FEC-label mappings
previously requested of and/or advertised by the peer. The MT TLV
will be added into the optional paramers' field.
The encoding for the Label Release Message is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Release (0x0403) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Label Release Message
9. Session Initialization Message with MT Capability
The session initializtion message is extended to contain the LDP MT
capability as an optional parameter. The extended session
initialization message has the format below.
Zhao, et al. Expires January 9, 2012 [Page 16]
Internet-Draft LDP Multi Topology Extension July 2011
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Initialization (0x0200) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Session Parameters TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LDP MT Capability TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Session Initialization Message with MT Capability
10. MPLS Forwarding in MT
Although forwading is out of the scope of this draft. For the
completness of discussion, we include some forwarding consideration
for informational purpose here.
In MT based MPLS network, forwarding will be based not only on label,
but also on MT-ID associsted with the label. There are multiple
options to do this. Below, we list the option prefered.
10.1. Use Label for (FEC, MT-ID) Tuple
We suggest is that MPLS forwarding for different topologies is
implied by labels. This approach does not need any change to the
exsiting MPLS hardware forwarding mechanism. It also resolves the
forwarding issue that exists in IGP multi-topology forwarding when
multiple topologies share an interface with overlay address space.
On a MT awared LSR, each label is associated with tuple: (FEC,
MT-ID). Therefore, same FEC with different MT-ID would be assigned
to different labels.
Using this mechanism, for tuple (FEC-F, MT-ID-N1) and (FEC-F,
MT-ID-N2), each LSR along the LSP path that is shared by topology MT-
ID-N1 and MT-ID-N2 will allocate different labels to them. Thus two
different Label Switching Paths will be created. One for (FEC-F, MT-
ID-N1) and the other for (FEC-F, MT-ID-N1). The traffic for them
will follow different Label Switching Paths (LSPs).
Note, in this mechanism, label space is not allowed to be overlapping
Zhao, et al. Expires January 9, 2012 [Page 17]
Internet-Draft LDP Multi Topology Extension July 2011
among different MTs. In the above example, each label belongs to a
specific topology or the default topology. MPLS forwarding will be
performed exactly same as non-MT MPLS forwarding: using label to find
output information. This option will not require any change of
hardware forwarding to commodate MPLS MT. We will have different
RIBs coresspoding to different MT IDs. But we will only need one
LFIB.
Below is an example for MPLS forwarding:
RIB(x) for MT-IDx:
FEC NEXT HOP
FECi(Destination A) R1
RIB(y) for MT-IDy:
FEC NEXT HOP
FECi(Destination A) R2
LFIB:
Ingress Label Egress Label NEXT HOP
Lm Lp R1
Ln Lq R2 (could be same as R1)
Figure 11: Forwarding Mechanism
11. Security Consideration
MPLS security applies to the work presented. No specific security
issues with the proposed solutions are known. The authentication
procedure for RSVP signalling is the same regardless of MT
information inside the RSVP messages.
12. IANA Considerations
TBD
13. Acknowledgement
The authors would like to thank Dan Tappan, Nabil Bitar, and Huang
Zhao, et al. Expires January 9, 2012 [Page 18]
Internet-Draft LDP Multi Topology Extension July 2011
Xin for their valuable comments on this draft.
14. References
14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, June 2007.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120, February 2008.
14.2. Informative References
Authors' Addresses
Quintin Zhao
Huawei Technology
125 Nagog Technology Park
Acton, MA 01719
US
Email: qzhao@huawei.com
Huaimo Chen
Huawei Technology
125 Nagog Technology Park
Acton, MA 01719
US
Email: huaimochen@huawei.com
Zhao, et al. Expires January 9, 2012 [Page 19]
Internet-Draft LDP Multi Topology Extension July 2011
Emily Chen
Huawei Technology
No. 5 Street, Shangdi Information, Haidian
Beijing
China
Email: chenying220@huawei.com
Lianyuan Li
China Mobile
53A, Xibianmennei Ave.
Xunwu District, Beijing 01719
China
Email: lilianyuan@chinamobile.com
Chen Li
China Mobile
53A, Xibianmennei Ave.
Xunwu District, Beijing 01719
lichenyj
Email: lilianyuan@chinamobile.com
Lu Huang
China Mobile
53A, Xibianmennei Ave.
Xunwu District, Beijing 01719
China
Email: huanglu@chinamobile.com
Luyuang Fang
Cisco Systems
300 Beaver Brook Road
Boxborough, MA 01719
US
Email: lufang@cisco.com
Zhao, et al. Expires January 9, 2012 [Page 20]
Internet-Draft LDP Multi Topology Extension July 2011
Chao Zhou
Cisco Systems
300 Beaver Brook Road
Boxborough, MA 01719
US
Email: czhou@cisco.com
Ning So
Verison Business
2400 North Glenville Drive
Richardson, TX 75082
USA
Email: Ning.So@verizonbusiness.com
Raveendra Torvi
Juniper Networks
10, Technoogy Park Drive
Westford, MA 01886-3140
US
Email: pratiravi@juniper.com
Zhao, et al. Expires January 9, 2012 [Page 21]
