Enhanced Topology Independent Loop-free Alternate Fast Re-route
draft-li-rtgwg-enhanced-ti-lfa-04
RTGWG Working Group C. Li
Internet-Draft Z. Hu
Intended status: Standards Track Huawei Technologies
Expires: November 7, 2021 Y. Zhu
China Telecom
S. Hegde
Juniper Networks Inc.
May 6, 2021
Enhanced Topology Independent Loop-free Alternate Fast Re-route
draft-li-rtgwg-enhanced-ti-lfa-04
Abstract
Topology Independent Loop-free Alternate Fast Re-route (TI-LFA) aims
at providing protection of node and adjacency segments within the
Segment Routing (SR) framework. A key aspect of TI-LFA is the FRR
path selection approach establishing protection over the expected
post-convergence paths from the point of local repair. However, the
TI-LFA FRR path may skip the node even if it is specified in the SID
list to be traveled.
This document defines Enhanced TI-LFA(TI-LFA+) by adding a No-bypass
indicator for segments to ensure that the FRR route will not bypass
the specific node, such as firewall. Also, this document defines No-
bypass flag and No-FRR flag in SRH to indicate not to bypass nodes
and not to perform FRR on all the nodes along the SRv6 path,
respectively.
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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 7, 2021.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. Overview of Enhanced TI-LFA . . . . . . . . . . . . . . . . . 3
4. IGP Protocol Extensions . . . . . . . . . . . . . . . . . . . 4
4.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Flags in SRH . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. No-bypass Flag in SRH . . . . . . . . . . . . . . . . . . 8
5.2. No-FRR Flag in SRH . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Segment Routing [RFC8402] enables to steer packets by explicitly
encoding instructions in the data packets at the source node to
support services like traffic engineer. Relying on SR,
[I-D.ietf-rtgwg-segment-routing-ti-lfa] defines Topology Independent
Loop-free Alternate Fast Re-route (TI-LFA), a local repair mechanism
for IGP shortest path that capable of restoring end-to-end
connectivity in the case of a sudden directly connected failure of a
network component.
TI-LFA supports to establish a loop free backup path over the
expected post-convergence paths from the point of local repair
irrespective of the topologies used in the network, which provides a
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major improvment compared to LFA [RFC5286], and remote LFA [RFC7490]
which cannot be applicable in some topologies [RFC6571].
However, the TI-LFA path may skip the node that the active SID points
to when protecting [Adjacency, Node] segment lists. For instance,
the node that a adjacency SID points to is a very important node and
can not be skipped, such as a firewall node. When the link between
the local repair node and firewall node fails, the packets should be
steered back to the firewall and then forwarding. But in TI-LFA, if
the next SID in the SID list is a node SID, the TI-LFA FRR path MAY
bypass the node that the active segment points to. Also, if the
firewall node is down, the packets should be dropped instead for fast
reroute to bypass the node. Bypassing nodes like firewall in FRR
brings issues of network security and reliability.
To enhance the security and reliability of networks, this document
defines an Enhanced Topology Independent Loop-free Alternate Fast Re-
route (TI-LFA+) based on TI-LFA by adding a No-bypass flag for
segments to explicitly specify what node can not be bypassed. Also,
this document defines No-bypass flag and No-FRR flag in SRH to
indicate not to bypass nodes and not to perform FRR on all the nodes
along the SRv6 path, respectively.
2. Terminology
This document makes use of the terms defined in
[I-D.ietf-rtgwg-segment-routing-ti-lfa] and [RFC8402]. The reader is
assumed to be familiar with the terminology defined in
[I-D.ietf-rtgwg-segment-routing-ti-lfa] and [RFC8402].
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Overview of Enhanced TI-LFA
Enhanced Topology Independent Loop-free Alternate Fast Re-route (TI-
LFA+) is an enhancement of TI-LFA to explicitly indicate whether a
node that segment points to can not be bypassed in FRR scenarios.
TI-LFA+ will not change the main process and algorithm of TI-LFA.
Instead, in TI-LFA+, when generating repair SID list for a SID, the
node should consider whether the SID endpoint can be baseed or not,
which is explicitly encoded in IGP messages. If the node that
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segment points to can not be bypassed, then the repair SID MUST lead
the packets to that node. This document defines a No-bypass flag for
segments in IS-IS and OSPF. Details will be discussed in section 4.
A node should advertise two kinds of segment to meet various service
policy requirements.
o Bypassing capable segment with No-bypass flag unset
o No-bypassing segment with No-bypass flag set.
A controller or control plane should choose specific segment
according to the service policy.
[Editors' note] If the TI-LFA result is generated based on Locator
route instead of SIDs, then the No-bypass Flag can be applied to the
Locator.
Also, this document defines No-bypass flag and No-FRR flag in SRH to
indicate not to bypass nodes and not to perform FRR on all the nodes
along the SRv6 path, respectively. Details will be discussed in
section 5.
4. IGP Protocol Extensions
4.1. IS-IS
[RFC8667] describes the necessary IS-IS extensions that need to be
introduced for Segment Routing.[I-D.ietf-lsr-isis-srv6-extensions]
defines the IS-IS extensions required to support Segment Routing over
an IPv6 data plane. This documment defines a No-bypass flag in flag
filed of the following IS-IS sub-TLV/TLV.
o Prefix Segment Identifier sub-TLV (Prefix-SID sub-TLV) [RFC8667]
o Adjacency Segment Identifier sub- TLV (Adj-SID sub-TLV).[RFC8667]
o Locator entry in SRv6 Locator TLV
[I-D.ietf-lsr-isis-srv6-extensions]
The following figures are included here for reference and will be
deleted in the future version.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
|R | N| P| E| V| L|NB| |
+--+--+--+--+--+--+--+--+
Figure 1. Prefix-SID sub-TLV and No-bypass Flag
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
|F | B| V| L| S|NB| | |
+--+--+--+--+--+--+--+--+
Figure 2. Adj-SID sub-TLV and No-bypass Flag
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Loc Size | Locator (variable)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-tlv-len | Sub-TLVs (variable) . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
|D |NB| | | | | | |
+--+--+--+--+--+--+--+--+
Figure 3. SRv6 Locator Entry and No-bypass Flag
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If the No-bypass(NB) flag is set, means the node that the SID/Label/
Locator points to can not be bypassed. Oterwise, the node can be
bypassed.
4.2. OSPF
[RFC8665] describes the necessary OSPF extensions that need to be
introduced for Segment Routing.[I-D.ietf-lsr-ospfv3-srv6-extensions]
defines the OSPF extensions required to support Segment Routing over
an IPv6 data plane. This documment defines a No-bypass flag in flag
filed of the following OSPF sub-TLV/TLV.
o Prefix SID Sub-TLV [RFC8665]
o Adj-SID sub-TLV [RFC8665]
o SRv6 Node SID TLV [I-D.ietf-lsr-ospfv3-srv6-extensions]
o SRv6 SID Link Attribute Sub-TLV
[I-D.ietf-lsr-ospfv3-srv6-extensions]
The following figures are included here for reference and will be
deleted in the future version.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved | MT-ID | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| |NP|M |E |V |L |NB| |
+--+--+--+--+--+--+--+--+
Figure 4. Prefix-SID sub-TLV and No-bypass Flag
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved | MT-ID | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Label/Index (variable) |
+---------------------------------------------------------------+
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
|B | V| L| G| P|NB| | |
+--+--+--+--+--+--+--+--+
Figure 5. Adj-SID sub-TLV and No-bypass Flag
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Function-Flags| Function Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | SID Flags | SID-size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (variable - 32 bit aligned) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
|D |NB| | | | | | |
+--+--+--+--+--+--+--+--+
Figure 6. SRv6 Node SID TLV and No-bypass Flag
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Function-Flags| Function Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | SID Flags | SID-size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (variable - 32 bit aligned) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
|NB| | | | | | | |
+--+--+--+--+--+--+--+--+
Figure 7. SRv6 Adj-SID TLV and No-bypass Flag
If the No-bypass(NB) flag is set, means the node that the SID/Label/
Locator points to can not be bypassed. Oterwise, the node can be
bypassed.
5. Flags in SRH
This section describes two flags in SRH.
5.1. No-bypass Flag in SRH
This document defines a No-bypass Flag in SRH [RFC8754].
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
|NB| | | | | | | |
+--+--+--+--+--+--+--+--+
o NB Flag: No-Bypass flag, when the flag is set, the repair segment
endpoint nodes MUST NOT bypass any nodes when link or node
failures occur. When a link is down, the packet MUST be forwarded
to the next segment endpoint node through the repair path. When
the node identified by the active SID in IPv6 destination address
is down, the SID can not be skipped, and the traffic MUST be
forwarded to the node.
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The flag can be set when the SID list containing service SIDs like
firewall SID, so that the traffic will not bypass the service nodes.
5.2. No-FRR Flag in SRH
This document defines a No-FRR Flag in SRH [RFC8754].
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| |NF| | | | | | |
+--+--+--+--+--+--+--+--+
o NF Flag: No-FRR flag, when the flag is set, the FRR is disable for
the packet, thus the packet will not be protected by the Local
protection mechanism, such as TI-LFA.
The flag can be set when the SID list containing service SIDs like
firewall SID, so that the traffic will not bypass the service nodes.
In this case, E2E protection mechanism should be deployed.
6. IANA Considerations
TBD.
7. Security Considerations
TBD.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
IP Fast Reroute: Loop-Free Alternates", RFC 5286,
DOI 10.17487/RFC5286, September 2008,
<https://www.rfc-editor.org/info/rfc5286>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[RFC7490] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
RFC 7490, DOI 10.17487/RFC7490, April 2015,
<https://www.rfc-editor.org/info/rfc7490>.
[RFC6571] Filsfils, C., Ed., Francois, P., Ed., Shand, M., Decraene,
B., Uttaro, J., Leymann, N., and M. Horneffer, "Loop-Free
Alternate (LFA) Applicability in Service Provider (SP)
Networks", RFC 6571, DOI 10.17487/RFC6571, June 2012,
<https://www.rfc-editor.org/info/rfc6571>.
[I-D.ietf-rtgwg-segment-routing-ti-lfa]
Litkowski, S., Bashandy, A., Filsfils, C., Francois, P.,
Decraene, B., and D. Voyer, "Topology Independent Fast
Reroute using Segment Routing", draft-ietf-rtgwg-segment-
routing-ti-lfa-06 (work in progress), February 2021.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
8.2. Informative References
[RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, DOI 10.17487/RFC4657, September
2006, <https://www.rfc-editor.org/info/rfc4657>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
Extensions for Segment Routing", RFC 8667,
DOI 10.17487/RFC8667, December 2019,
<https://www.rfc-editor.org/info/rfc8667>.
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[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
[I-D.ietf-lsr-ospfv3-srv6-extensions]
Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak,
"OSPFv3 Extensions for SRv6", draft-ietf-lsr-
ospfv3-srv6-extensions-02 (work in progress), February
2021.
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extension to Support Segment Routing over
IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-14
(work in progress), April 2021.
Authors' Addresses
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: c.l@huawei.com
Zhibo Hu
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: huzhibo@huawei.com
Yongqing Zhu
China Telecom
Email: zhuyq8@chinatelecom.cn
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Shraddha Hegde
Juniper Networks Inc.
India
Email: shraddha@juniper.net
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