Network Working Group S. De Cnodder
Internet Draft C. Pelsser
Expiration Date: March 2004
September 2003
Protection for inter-AS MPLS tunnels
draft-decnodder-mpls-interas-protection-01.txt
Status of this Memo
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Abstract
This document describes a solution for link protection, node
protection, Shared Risk Link Group (SRLG) protection and fast
recovery of inter-AS LSPs. These problems are highlighted in [ASREQ].
The proposed solution is based on RSVP-TE [RFC3209] as recommended by
[ASREQ].
1. Introduction
This document describes a solution for the following requirements
from [ASREQ]:
1) link protection
2) node protection
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3) SRLG protection
4) fast recovery
5) based on RSVP-TE [RFC3209]
MPLS Fast-Reroute techniques based on [FRR] together with the RSVP
objects Exclude Route Object (XRO) and Explicit Exclude Route
Subobject (EXRS), as defined in [XRO], will be used to fulfill the
above requirements. Only the protection of links between 2 ASs, the
protection of their SRLGs and the protection of nodes at the border
of an AS are in the scope of this document.
Section 3 proposes to tunnel inter-AS LSPs through intra-AS LSPs
inside an AS, as described in [HIER]. This tunneling favors the
confidentiality requirement concerning intra-AS topologies [ASREQ] as
well as the establishment of inter-AS LSPs. The establishment of
inter-AS LSPs will not be studied further in this draft. In this
document it is assumed that ASes define their SRLGs independent from
the SRLGs in other ASes.
Section 4 shows that an end-to-end backup LSP can only provide link
and node protection. For SRLG protection and fast recovery, the
methods in [FRR] have to be used. These methods are described in
section 6 for detour LSPs and the use of bypass tunnels to protect
inter-AS LSPs is introduced in section 7. Nodes other than those
mentioned in this document, must use the methods in [FRR] to
establish detour LSPs or bypass tunnels. This means that these nodes
establish detour LSPs that merge with the main LSP in the same AS
where they are originated, or these nodes establish bypass tunnels
that terminate in the same AS as where they originate.
2. Summary for Sub-IP Area
<TBD>
3. Inter-AS LSP tunneled through an intra-AS LSP
To improve scalability and confidentiality (which is outside the
scope of this document), an inter-AS LSP can be tunneled through an
intra-AS LSP [HIER]. For instance, in Figure 2, the link between R23
and R24 could be an LSP passing multiple core routers. And, the
inter-AS LSP is tunneled through this LSP.
The procedures described in the following sections apply for inter-AS
link, node and SRLG protection of inter-AS LSPs whether they are
tunneled or not.
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4. Problems to protect SRLGs with disjoint end-to-end LSPs
The motivation to support fast-reroute techniques as described in
[FRR] is twofold: first of all, it supports fast recovery and
secondly, it can also provide SRLG protection, which is not the case
for a disjoint end-to-end LSP. The problems to support SRLG
protection, with the latter method, are described in this section.
There are different ways to provide end-to-end protection of inter-AS
LSPs. A first possibility is to establish a secondary path that
crosses different ASs than the main LSP. An alternative is to
establish an LSP that follows the same AS path to the destination as
the main LSP, i.e. it crosses the same ASs in the same order, but is
link or node disjoint from the main LSP. However, these two solutions
do not permit to establish an LSP that is disjoint from the SRLGs of
the main LSP. That is, it is not possible to protect the main inter-
AS LSP against SRLGs failures with a single end-to-end link or node
disjoint LSP. This is due to the fact that ASs may possess links
belonging to the same SRLG even if these ASs do not have the same
convention to designate this SRLG.
AS1 AS2 AS3
/----------\ /-------------- \ /------------\
R12 ---- R21 ---- R23 ---- R31
/ \ \
/ \ \
R11 R25 R33
\ \ /
\ \ /
R13 ---- R22 ---- R24 ---- R32
Figure 1: end-to-end SRLG protection
For example, on figure 1, we have a main LSP going from R11 in AS1 to
R33 in AS3 through R13, R22, R24 and R32. It is not possible to
protect this LSP against SRLG failures with a backup LSP crossing
R12, R21, R23 and R31. This is because AS3 could have links which
have SRLGs in common with links in AS1 and AS1 nor AS3 will be aware
of it. For example, link R11-R13 and link R31-R33 may belong to the
same SRLG. This example relies on the fact that different ASs may use
the same resources to join different nodes in their respective
domain. A similar situation occurs when the main and the backup LSP
do not share the same AS path but instead partially cross different
ASs.
This document only focuses on local protection as defined in [FRR],
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because it is not possible to provide full protection of an inter-AS
LSP with a single end-to-end LSP. The solution proposed in this
document enables the provision of link, node and SRLG protection of
inter-AS LSPs.
5. Network model and terminology
To illustrate the procedures described in the next sections, the
following network model is used:
AS1 AS2
/-------------\ /------------\
+---+ +---+ +---+ +---+
------|R11|---|R12|------|R21|---|R22|------
+---+ +---+ +---+ +---+
| | | |
| | | |
| | | |
+---+ +---+ +---+ +---+
------|R13|---|R14|------|R23|---|R24|------
+---+ +---+ +---+ +---+
Figure 2: a reference network model
The main LSP is established from a certain node (not shown on the
figure) and goes over routers R13, R14, R23, and R24 towards the
destination (also not shown on the figure). AS1 is referred to as the
upstream AS of AS2, and AS2 is referred to as the downstream AS of
AS1.
An "egress AS-BR" or a "primary egress AS-BR" is an Autonomous System
Border Router (AS-BR) at which the main LSP leaves an AS. In the
network example, in figure 2, this is router R14, inside AS1.
An "ingress AS-BR" or a "primary ingress AS-BR" is an AS-BR at which
the main LSP enters an AS. In the network example, this is router
R23, inside AS2.
A "secondary egress AS-BR" is an AS-BR at which the bypass tunnel or
the detour LSP leaves an AS. In the network example, this could be
router R12, in AS1.
A "secondary ingress AS-BR" is an AS-BR at which the bypass tunnel or
the detour LSP enters an AS. In the network example, this could be
router R21, in AS2.
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"Inter-AS link protection" is the protection of an LSP against a
failure of the link connecting two ASs on the path of the LSP. In the
network example, the inter-AS link R14-R23 is to be protected.
"Inter-AS node protection" is the protection of an LSP against an
AS-BR failure. This can be the egress AS-BR, R14, or the ingress AS-
BR, R23, for the considered example.
"Inter-AS SRLG protection" is the protection of an LSP against a
simultaneous failure of all links that belong to certain SRLGs which
also contain the inter-AS link (R14-R23 in figure 2).
Other terminology and abbreviations are taken from [FRR].
6. Protection with detour LSPs
6.1 Link protection with detour LSPs
6.1.1 Procedures for the egress AS-BR
The primary egress AS-BR has to establish a detour LSP to protect the
interdomain link. The destination of the detour LSP will be the same
as the destination of the main LSP. The detour LSP may merge with the
main LSP at any downstream node or with other detour LSPs of the same
main LSP, established by nodes downstream of the link to be
protected. The egress AS-BR has to determine a secondary egress AS-BR
and then it can perform a path calculation towards this AS-BR.
The primary egress AS-BR can select any other AS-BR as secondary
egress AS-BR but it is recommended to select an AS-BR that is
connected to the downstream AS of the main LSP (i.e. the AS where the
primary ingress AS-BR is located). In case this condition is not met,
it could be for instance possible that the downstream AS of the
detour LSP chooses a path that goes through the AS where the detour
LSP was originated which can cause loops. In addition, it is
recommended that the detour LSP merges in the AS where this
downstream ingress AS-BR is located (the merging node could be the
ingress AS-BR itself) if the destination of the main LSP is not in
the downstream AS (AS2 in Figure 2). This suggestion improves the
scalability of the solution since merging of LSPs diminishes the
number of states to be maintained, the bandwidth to be reserved, and
so on. Therefore, the egress AS-BR should put a portion of the RRO of
the main LSP inside the ERO of the detour LSP. The last hop in the
downstream AS (the egress AS-BR in the downstream AS) of the main LSP
and all hops after that router should be at least in the ERO of the
detour LSP. In addition to this portion of the RRO of the main LSP,
the ERO may be further prepended by the egress AS-BR with a strict or
a loose path towards the selected secondary egress AS-BR. That is,
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the ERO of the detour LSP at least contains: (1) A strict or loose
path toward the secondary egress ASBR (2) The path of the main LSP
starting at the last hop inside the downstream AS and ending at the
destination of the main LSP. In the example network, we have a main
LSP with RRO containing routers R11, R12, R21, R22, etc. The ERO of
the detour LSP protecting link R12-R21 is composed of router R14, R22
(with loose flag set) and the following routers.
There are two possible methods to determine the secondary egress AS-
BR at the primary egress AS-BR. (1) The egress AS-BR can be manually
configured with other AS-BRs that peer to the same AS or (2) it can
lookup in its BGP table to find an other entry such that the AS-path
has the same AS next hop as the currently selected entry. Option (1)
is feasible because the number of links between 2 ASs is usually
limited to only a small number of links.
It could be possible that the primary egress AS-BR is the same router
as the secondary egress AS-BR and that the primary ingress AS-BR is
the same router as the secondary ingress AS-BR. In this particular
case the inter-domain link on the primary path must not be the same
link used by the detour LSP and no path calculation should be done to
calculate a (partial) path for the detour LSP.
The use of the LSP-Merge subobject, defined in Appendix A, is
optional to provide link protection.
6.1.2 Procedures for the ingress AS-BR
No extra procedures are required.
The detour LSP may merge with the main LSP at this node.
6.1.3 Procedures for the secondary egress AS-BR
The secondary egress AS-BR completes the path in the ERO by selecting
a secondary ingress AS-BR in the downstream AS. If there is no ERO
present, then the tunnel end point address in the Session object has
to be used to route the Path message.
6.1.4 Procedures for the secondary ingress AS-BR
The secondary ingress AS-BR completes the ERO with a path towards the
next subobject in the ERO. The LSP should merge with the main LSP at
the node that processes the LSP-Merge subobject (if that subobject is
used), if it was not yet merged at this point. If no ERO is present
inside the Path message of the detour LSP, the path is computed based
on the tunnel end point address.
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6.2 Node protection with detour LSPs
The procedures and recommendations are the same for the protection of
an ingress AS-BR failure as for link protection, with the exception
that the egress AS-BR has to include an XRO object or an EXRS
subobject [XRO] with the ingress AS-BR to exclude.
For the protection of the egress AS-BR, the same holds except that
the procedures apply to the router on the path of the main LSP
preceding the egress AS-BR. The method to determine a secondary
egress AS-BR is the same as for the egress AS-BR for link protection:
either manual configuration or by using BGP routing information, if
it is available. Note that the first solution requires more
configuration as for link protection in case this router peers with
more than one AS-BR.
6.3 SRLG protection with detour LSPs
Similar procedures as for link protection apply for SRLG protection.
In addition, the secondary egress AS-BR must be an AS-BR that peers
with the downstream AS of the primary LSP. And, the detour LSP must
merge at that AS. The former condition is necessary because only the
two peering ASs know the SRLGs of the inter-domain link and the
latter condition implies that the LSP-Merge subobject must be used.
This subobject is inserted inside the ERO to indicate the node where
merging needs to be done (see appendix A). The next subsections
describe in more details the procedures to be performed at the nodes
involved in the establishment of such detour LSP.
6.3.1 Procedures for the egress AS-BR
The egress AS-BR has to include an XRO object or an EXRS subobject to
exclude the SRLGs of the inter-domain link. The XRO or the EXRS must
include a list of SRLGs (defined for the AS containing the PLR)
corresponding to the inter-AS link as well as a reference to this
link. If the egress AS-BR can calculate a strict path to reach the
secondary egress AS-BR, then the list of SRLGs may be removed. Only
the reference to the link for which the detour LSP has to be SRLG
disjoint is then required (see section 6.3.2). The secondary ingress
AS-BR has to use the information in the XRO or EXRS to further
calculate a path for the detour LSP.
To ensure merging inside the downstream AS, the LSP-Merge subobject
(see Appendix A) has to be included in the ERO by the egress AS-BR.
The LSR where the detour LSP is merged with the main LSP has to
ensure that it can perform a switch-over from the incoming detour LSP
containing the LSP-Merge subobject to its originating detour LSP in
case the next link has an SRLG in common with the inter-domain link.
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This is because in this case, both links can fail at the same time
such that both detour LSPs will be activated at the same time.
6.3.2 Procedures for the secondary egress AS-BR
The secondary egress AS-BR selects a next hop and the XRO or EXRS
contains a reference to the link for which the detour LSP has to be
SRLG disjoint. No list of SRLGs should be included because the SRLG
IDs are local to an AS, which means that if a list of SRLG IDs would
be sent to the next hop, then this node would not understand the IDs.
Therefore only the reference to the inter-AS link is useful. This
link is referenced by means of its IP address, see [XRO]. The
secondary egress AS-BR thus removes the list of SRLGs related to the
inter-AS link, if such a list of SRLGs was present.
6.3.3 Procedures for the ingress AS-BR
No extra procedures required.
6.3.4 Procedures for the secondary ingress AS-BR
If the secondary ingress AS-BR cannot compute a full path towards the
node immediately preceeding the LSP-merge subobject, then the
secondary ingress AS-BR adds the list of SRLGs of the inter-AS link
present inside the received XRO or EXRS inside these objects. These
SRLGs are known by the nodes inside this AS. This is required because
the LSP can cross nodes inside the AS which do not know the SRLGs of
the inter-AS link, but only the SRLGs of intra-area links. An
alternative would be to distribute inter-AS links and their SRLGs
inside the IGP.
6.3.5 Path calculation
To allow the egress AS-BR and the secondary ingress AS-BR to
calculate a path, the SRLGs of the inter-AS links towards the same
downstream AS (upstream AS, respectively) as the main LSP have to be
known. This could be achieved through manual configuration of the
SRLGs of other inter-AS links to the same downstream/upstream AS at
each AS-BR. For instance, in Figure 2, at R14 and R23, the SRLGs of
R12-R21 can be configured such that they are known for the path
calculation, and at R12 and R21, the SRLGs of R14-R23 can be
configured. An other option is to flood this information via BGP
extensions to be defined or to distribute these links and their SRLGs
inside the IGP. It is not assumed that nodes other than AS-BRs having
a link to the same downstream/upstream AS know the SRLGs of these
inter-AS links. If this would be the case, then the procedures above
can be simplified, e.g., the egress AS-BR in Section 6.3.1 does not
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have to include a list of SRLGs anymore when only a partial path can
be computed.
Also the secondary egress AS-BR has to know the SRLGs of the inter-AS
link used by the primary LSP. This is to allow the egress AS-BR to
select a link in case there are multiple links towards the downstream
AS, and to check if the link is indeed SRLG disjoint from the inter-
AS link used by the main LSP.
6.3.6 SRLG and node protection
Protection of the egress AS-BR and SRLG protection of the link
preceding the egress AS-BR is best solved by using two detour LSPs at
the node on the path of the main LSP preceding the egress AS-BR: a
detour to protect against the SRLGs of the intra-domain link and a
second detour LSP that is established using the procedures for node
protection as described in the previous section. The detour
protecting against the SRLGs has to merge in the same AS, i.e. it has
to merge with the main LSP at the egress AS-BR. This is because other
ASs do not know this intra-domain link, nor its SRLGs. To ensure that
merging occurs at the egress AS-BR, the RRO of the main LSP should be
fully included in the ERO of the detour LSP together with the LSP-
Merge subobject. This path should be preceded by a path, which is
SRLG disjoint with the next link of the main LSP computed towards the
egress AS-BR. This could only be a partial path towards the egress
AS-BR in which case an XRO object or an EXRS subobject, containing
the SRLGs to avoid, has to be added. It has to be ensured that these
2 detour LSPs do not merge, which means that at least one of the
detour LSP should be a sender-template specific detour LSP.
The egress AS-BR must ensure that it can do a switch-over from the
incoming detour LSP protecting against a failure of the preceding
link to its originating detour LSP. This is because the preceding
link and the inter-domain link can belong to the same SRLG, hence
they can fail at the same time. For this reason, the LSP-Merge
subobject must be used in this case.
If protection of the ingress AS-BR is requested, in addition to SRLG
protection, the egress AS-BR also has to put the ingress AS-BR in the
XRO or EXRS like it was done for node protection.
The use of 2 detour LSPs (one for SRLG protection and the other for
node protection) is also recommended when the ingress AS-BR is to be
protected. If only 1 detour LSP is used, and the LSP only crosses 1
hop in the downstream AS (i.e. ingress AS-BR and egress AS-BR in the
downstream AS are the same router), the detour LSP setup would fail.
This is because the AS further downstream of the immediate downstream
AS is not aware anymore of the SRLGs of the link to be protected.
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In case of node and SRLG protection or in case of SRLG protection
only, it is recommended to use sender-template specific detour LSPs
to avoid that detour LSPs merge with each other.
7. Protection with bypass tunnels
The problem of protection by means of bypass tunnels can be split
into two parts:
a) The bypass tunnel has to be signaled over a path that is disjoint
with the network resources that it protects.
b) After the bypass tunnels are established, an appropriate bypass
tunnel has to be selected for each particular main LSP such that the
protection requirements for that LSP are met.
The first part is very similar to the establishement of detour LSPs:
an XRO object or an EXRS subobject can be used to signal the bypass
tunnel such that it is disjoint from the network resources used by
the main LSP. The same recommendations as for detour LSPs apply, i.e.
it is recommended that the downstream AS of the bypass tunnel and the
main LSP are the same AS. Additionally, as two detour LSPs are
required for SRLG protection of the upstream link of an egress ASBR
and the egress ASBR itself, two bypass tunnels are also required to
protect these resources. Note that the LSP-Merge subobject is not
used for bypass tunnels as it was the case for detour LSPs because
bypass tunnels do not merge with the main LSP at the far-end of the
bypass tunnel, but they are terminated at that node.
The difficulty in providing protection with bypass tunnels relies in
the selection of appropriate bypasses for the protection of given
resources.
To select a bypass tunnel, the PLR has to take a bypass tunnel that
it originates and that fulfills the following requirements:
a) The bypass tunnel must fulfill the appropriate constraints
(bandwidth, link affinities, ...).
b) The bypass tunnel must be disjoint with the link/node/SRLGs to be
protected.
c) The destination of the bypass tunnel must be the next-hop node
(resp. next-next-hop node) of the main LSP, or a node further
downstream on the path of the main LSP, in case of link protection
(resp. node protection).
The first two requirements can be achieved since all required
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information is locally available in the PLR. This is because the PLR
has established the candidate bypass tunnels, hence it knows the
bandwidth and the resources protected by the bypass tunnel. Complying
with the third requirement is more difficult. Generally, the PLR must
check if the destination of the bypass tunnel belongs to one of the
nodes listed in the RRO of the Resv message of the main LSP. Usually
the RRO contains interface addresses and the destination of a bypass
tunnel may be a different interface address or the node-id of a
router. This means that the PLR has to map the addresses listed in
the RRO of the main LSP to the destination address of the bypass
tunnel. In an intra-area environment this is possible since this
information is available in the IGP topology, but in the inter-AS
case, this information is not anymore available locally in the PLR.
There are multiple methods to solve this problem:
Solution A: use [NODEID] where the node-id of the routers are put in
the RRO of the Resv message of the main LSP and the node-id is also
put in the RRO of the Resv message of the bypass tunnel if the
destination was not the node-id. In this way, the PLR simply has to
compare the node-ids in the RRO of the main LSP with the destination
of the bypass tunnel or with the node-id in the RRO of the bypass
tunnel.
Solution B: use the interface address that would be recorded in the
RRO of the main LSP as destination of the bypass tunnel. For
instance, when the link between ASBR1 and ASBR2 is to be protected,
the destination address would be the address of the interface on
ASBR2 towards ASBR1. If this link is unnumbered, the destination
address used is the node-id that is mentioned in the RRO of the main
LSP. This is sufficient to identify the common node on the primary
and the bypass tunnel. When node protection is to be provided and the
destination of the Bypass Tunnel is the next-hop of the protected
node (next-next hop from the PLR point of view), the destination of
the bypass tunnel should be the address of the interface on the
next-next-hop router that goes towards the node being protected.
Multiple bypass tunnels must be used in case of parallel links. We
also note that a failure of the interface used as destination of the
bypass tunnel does not lead to the failure of the bypass tunnel
itself (this is in particular important for link protection).
Until now, we supposed that the bypass tunnels were manually
configured, with the destination being part of the configuration.
But, bypass tunnels can also be signaled automatically when the first
main LSP is established. Therefore, we have to determine the
destination of these dynamically established bypass tunnels. In case
of solution B, the information about the interface addresses in the
RRO of the main LSP can be used as a destination address. In case the
node-id is put in the RRO, then this node-id can be used.
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8. Security Considerations
TBD
Acknowledgments
This work was partially supported by the European Commission within
the IST ATRIUM project. The authors would like to thank Dimitri
Papadimitriou and Olivier Bonaventure for their useful comments.
References
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
Swallow, G., "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209,
December 2001.
[ASREQ] Zhang, R., Vasseur, JP., (Editors), "MPLS Inter-AS Traffic
Engineering requirements", draft-ietf-tewg-interas-mpls-te-req-
00.txt, work in progress.
[FRR] Pan, P., Atlas, A. (Editors), "Fast Reroute Extensions to
RSVP-TE for LSP Tunnels", draft-ietf-mpls-rsvp-lsp-fastreroute-
03.txt, work in progress.
[XRO] Lee, CY., Farrel, A., De Cnodder, S., "Exclude Routes -
Extension to RSVP-TE", draft-ietf-ccamp-rsvp-te-exclude-route-00.txt,
work in progress.
[HIER] Kompella, K., Rekhter, Y., "LSP Hierarchy with Generalized
MPLS TE", draft-ietf-mpls-lsp-hierarchy-08.txt, work in progress.
[NODEID] Vasseur, J.-P., Ali, Z., Sivabalan, S., "Definition of an
RRO node-id subobject", draft-ietf-mpls-nodeid-subobject-01.txt, work
in progress.
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Authors Addresses
Stefaan De Cnodder
Email: stefaan.de_cnodder@alcatel.be
Cristel Pelsser
Infonet group (FUNDP)
Rue Grandgagnage 21, B-5000 Namur, Belgium
Email: cpe@info.fundp.ac.be
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Appendix A: LSP-Merge subobject
The LSP-Merge subobject is a new subobject in the Explicit Route
Object (ERO). The procedures defined in [RFC3209] section 5.3.4.1 to
select the next hop are modified as follows: if after step 3 of the
next hop selection process the node finds an LSP-Merge subobject in
front of the ERO, i.e. the LSP-Merge subobject is the first subobject
in the ERO after removing the subobjects belonging to the local
abstract node, then the LSP has to merge with an LSP with the same
Session object and LSP ID at the current node, if such an LSP exists.
If no such LSP exists, then the detour LSP is rejected and a ResvErr
with errorcode TBD is sent to the originating node.
The LSP with which the LSP containing the LSP-Merge subobject merges
must be a main LSP, i.e. it may not contain a DETOUR object. In addi-
tion the abstract node where the merging occurs must ensure that in
case of a failure, the traffic can be switched from the LSP contain-
ing the LSP-Merge subobject to a backup LSP that was established by
the merging node to protect the main LSP. If these merging conditions
cannot be met, the "SRLG protection available" flag inside RRO subob-
jects, of appendix B, is set to zero. This indicates to the source
that SRLG protection is not provided for the main LSP.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Resvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L
Set to zero.
Type
TBD.
Length
The length field is set to 4.
Resvd
Set to zero on transmission and ignored on reception.
De Cnodder, Pelsser Expires March 2004 [Page 14]
Internet Draft draft-decnodder-mpls-interas-protection September 2003
Appendix B: SRLG protection desired
Currently [FRR] does not specify how SRLG protection can be requested
by the Head-End LSR. One way to do this is to define an "SRLG protec-
tion desired" flag in session attribute object. We will not further
investigate this since it is outside the scope of this document. i
In case two detours or bypass tunnels are available to provide SRLG
and node protection, then the "local protection available" flag is
set in the corresponding RRO subobject. Similarly, the "bandwidth
protection" flag of the RRO subobject is set when both detours or
bypass tunnels provide the requested bandwidth. Note that in case of
SRLG protection, it is recommended to use sender-template specific
detour LSP to avoid merging with other LSPs.
De Cnodder, Pelsser Expires March 2004 [Page 15]