One document matched: draft-mirsky-mpls-bfd-directed-04.xml
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<rfc category="std" ipr="trust200902" docName="draft-mirsky-mpls-bfd-directed-04">
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
<front>
<title abbrev='BFD Directed Return Path'>Bidirectional Forwarding Detection (BFD) Directed Return Path</title>
<author initials='G.' surname="Mirsky" fullname='Greg Mirsky'>
<organization>Ericsson</organization>
<address>
<email>gregory.mirsky@ericsson.com</email>
</address>
</author>
<author initials='J.' surname="Tantsura" fullname='Jeff Tantsura'>
<organization>Ericsson</organization>
<address>
<email>jeff.tantsura@ericsson.com</email>
</address>
</author>
<author initials='I.' surname="Varlashkin" fullname='Ilya Varlashkin'>
<organization>Google</organization>
<address>
<email>Ilya@nobulus.com</email>
</address>
</author>
<author fullname="Mach(Guoyi) Chen" initials="M." surname="Chen">
<organization>Huawei</organization>
<address>
<postal>
<street/>
<city/>
<code/>
<country/>
</postal>
<email>mach.chen@huawei.com</email>
</address>
</author>
<date day="8" month="August" year="2015" />
<area>Routing</area>
<workgroup>MPLS Working Group</workgroup>
<keyword>Internet-Draft</keyword>
<keyword>LSP Ping</keyword>
<keyword>BFD </keyword>
<abstract>
<t>
Bidirectional Forwarding Detection (BFD) is expected to monitor bi-directional paths.
When a BFD session monitors in its forward direction an explicitly routed path there is
a need to be able to direct egress BFD
peer to use specific path as reverse direction of the BFD session.
</t>
</abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>
RFC 5880 <xref target="RFC5880"/>, RFC 5881 <xref target="RFC5881"/>, and RFC 5883 <xref target="RFC5883"/> established the BFD
protocol for IP networks and RFC 5884 <xref target="RFC5884"/> set rules of using BFD asynchronous mode over IP/MPLS LSPs.
All standards implicitly assume that the egress BFD peer will use the shortest path route regardless of route being used to send BFD
control packets towards it. As result, if the ingress BFD peer sends its BFD control packets over explicit path that is diverging from
the best route, then reverse direction of the BFD session is likely not to be on co-routed bi-directional path with
the forward direction of the BFD session. And because
BFD control packets are not guaranteed to cross the same
links and nodes in both directions detection of Loss of Continuity (LoC) defect
in forward direction may demonstrate positive negatives.
</t>
<t>
This document defines the extension to LSP Ping <xref target="RFC4379"/>, BFD Reverse Path TLV, and proposes
that it to be used to instruct the egress BFD
peer to use explicit
path for its BFD control packets associated with the particular BFD session.
The TLV will be allocated from the
TLV and sub-TLV registry defined by RFC 4379 <xref target="RFC4379"/>.
As a special case, forward and reverse
directions of the BFD session can form bi-directional co-routed associated channel.
</t>
<section title="Conventions used in this document">
<section title="Terminology">
<t>BFD: Bidirectional Forwarding Detection
</t>
<t>MPLS: Multiprotocol Label Switching
</t>
<t>LSP: Label Switching Path
</t>
<t>LoC: Loss of Continuity
</t>
</section>
<section title="Requirements Language">
<t>
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
<xref target="RFC2119"></xref>.
</t>
</section>
</section>
</section>
<section anchor="problem-statement" title="Problem Statement">
<t>
BFD is best suited to monitor bi-directional co-routed paths.
<!--In most cases, in IP and IP/MPLS networks the best
route between two IP nodes is likely to be co-routed in the stable network environment so that implicit BF
D
requirement is being fulfilled. -->
In most cases, given stable environments, the forward and reverse direction between two nodes is
likely to be co-routed, this fulfilling the implicit BFD requirements.
If BFD is used to monitor unidirectional explicitly routed paths, e.g. MPLS-TE LSPs, its control
packets in forward direction would be in-band using the mechanism defined in <xref target="RFC5884"/> and <xref target="RFC5586"/>.
But the reverse direction of the BFD session would still follow the shortest path route and that might lead to the
following problems detecting failures on the unidirectional explicit path:
<list style="symbols">
<t>
detection of a failure on the reverse path cannot reliably be interpreted as bi-directional defect and thus trigger,
for example, protection switchover of the forward direction;
</t>
<t>
if a failure of the reverse path had been ignored, the ingress node would not receive indication of forward direction
failure from its egress peer.
</t>
</list>
</t>
<t>
To address these challenges the egress BFD peer should be instructed to use specific path for its control packets.
</t>
</section>
<section anchor="direct-reverse-bfd" title="Direct Reverse BFD Path">
<section anchor="mpls-plane" title="Case of MPLS Data Plane">
<t>
LSP ping, defined in <xref target="RFC4379"/>, uses BFD Discriminator TLV <xref target="RFC5884"/> to bootstrap a BFD
session over an MPLS LSP.
This document defines a new TLV, BFD Reverse Path TLV, that MUST contain a single sub-TLV
that can be used to carry information about reverse path for the specified in BFD Discriminator TLV session.
</t>
<section anchor="bfd-reverse-path-tlv" title="BFD Reverse Path TLV">
<t>
The BFD Reverse Path TLV is an optional TLV within the LSP ping protocol. However, if used, the BFD Discriminator TLV
MUST be included in an Echo Request message as well. If the BFD Discriminator TLV is not present when the BFD Reverse
Path TLV is included, then it MUST be treated as malformed Echo Request, as described in <xref target="RFC4379"/>.
</t>
<t>
The BFD Reverse Path TLV carries the specified path that BFD control packets of the BFD session referenced in the BFD
Discriminator TLV are required to follow. The format of the BFD Reverse Path TLV is as presented in <xref target="mpls-bfd-tlv"/>.
</t>
<t>
<figure align="left" anchor="mpls-bfd-tlv"
title="BFD Reverse Path TLV">
<artwork><![CDATA[
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFD Reverse Path TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Path |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</t>
<t>
BFD Reverse Path TLV Type is 2 octets in length and value to be assigned by IANA.
</t>
<t>
Length is 2 octets in length and defines the length in octets of the Reverse Path field.
</t>
<t>
Reverse Path field contains a sub-TLV. Any Target FEC sub-TLV, already or in the future defined, from IANA sub-registry
Sub-TLVs for TLV Types 1, 16, and 21 of MPLS LSP Ping Parameters registry MAY be used in this field.
Only one sub-TLV MUST be included in the Reverse Path TLV. If more than one sub-TLVs are present
in the Reverse Path TLV, then only the first sub-TLV MUST be used and the rest MUST be silently discarded.
</t>
<t>
If the egress LSR cannot find
path specified in the Reverse Path TLV it MUST send Echo
Reply with the received Reverse Path TLV and set the return code to "Failed to establish the
BFD session. The specified reverse path was not found" <xref target="return-codes"/>.
The egress LSR MAY establish the BFD session over
IP network according to <xref target="RFC5884"/>.
</t>
</section>
<section anchor="explicit-sub-tlv" title="Static and RSVP-TE sub-TLVs">
<t>
When explicit path on MPLS data plane set either as Static or RSVP-TE LSP
respective sub-TLVs defined in <xref target="RFC7110"/> identify explicit return path.
</t>
</section>
<section anchor="spring-sub-tlv" title="Segment Routing Tunnel sub-TLV">
<t>
In addition to Static and RSVP-TE, Segment Routing with MPLS data plane
can be used to set explicit path.
In this case a new sub-TLV is defined in this document as presented in <xref target="spring-mpls-sub-tlv"/>.
</t>
<t>
<figure align="left" anchor="spring-mpls-sub-tlv"
title="Segment Routing MPLS Tunnel sub-TLV">
<artwork><![CDATA[
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SegRouting MPLS sub-TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Entry 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Entry 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Entry N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</t>
<t>
The Segment Routing Tunnel sub-TLV Type is two octets in length, and will be allocated by IANA.
</t>
<t>
The egress LSR MUST use the Value field as label stack for BFD control packets
for the BFD session identified by source IP address and value in BFD Discriminator TLV.
</t>
<t>
The Segment Routing Tunnel sub-TLV MAY be used in Reply Path TLV defined in <xref target="RFC7110"/>
</t>
</section>
</section>
<section anchor="ipv6-plane" title="Case of IPv6 Data Plane">
<t>
IPv6 can be data plane of choice for Segment Routed tunnels <xref target="I-D.previdi-6man-segment-routing-header"/>.
In such networks the BFD Reverse Path TLV described in <xref target="bfd-reverse-path-tlv"/> can be used as well.
<!-- IP networks, unlike IP/MPLS, do not require use of LSP ping with BFD Discriminator TLV<xref target="RFC4379"/> to bootstrap BFD session.
-->
To specify reverse path of a BFD session in IPv6 environment the BFD Discriminator TLV MUST be used along with
the BFD Reverse Path TLV. The BFD Reverse Path TLV in IPv6 network MUST include sub-TLV.
</t>
<t>
<figure align="left" anchor="spring-ipv6-sub-tlv"
title="Segment Routing IPv6 Tunnel sub-TLV">
<artwork><![CDATA[
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SegRouting IPv6 sub-TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Prefix |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Prefix |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</t>
</section>
<section anchor="seg-rout-oper" title="Bootstrapping BFD session with BFD Reverse Path over Segment Routed tunnel">
<t>
As discussed in <xref target="I-D.kumarkini-mpls-spring-lsp-ping"/> introduction of Segment Routing network domains
with MPLS data plane adds three new sub-TLVs that may be used with Target FEC TLV. Section 6.1 addresses use of
new sub-TLVs in Target FEC TLV in LSP ping and LSP traceroute. For the case of LSP ping the <xref target="I-D.kumarkini-mpls-spring-lsp-ping"/>
states that:</t>
<t>
"Initiator MUST include FEC(s) corresponding to the destination
segment.
</t>
<t>
Initiator, i.e. ingress LSR, MAY include FECs corresponding to some or all of
segments imposed in the label stack by the ingress LSR to
communicate the segments traversed.
"
</t>
<t>
When LSP ping is used to bootstrap BFD session this document updates this and defines that LSP Ping MUST include the FEC corresponding
to the destination segment and SHOULD NOT include FECs corresponding to some or all of segment imposed by the ingress LSR. Operationally
such restriction would not cause any problem or uncertainty as LSP ping with FECs corresponding to some or all segments or traceroute
MAY precede the LSP ping that bootstraps the BFD session.
</t>
</section>
<section anchor="return-codes" title="Return Codes">
<t>
This document defines the following Return Codes:
<list style="symbols">
<t>
"Failed to establish the BFD session. The specified reverse path was not found", (TBD4).
When a specified reverse path is not available at the egress LSR, an Echo Reply with the return
code set to "Failed to establish the BFD session. The specified reverse path was not found"
MUST be sent back to the ingress LSR <xref target="bfd-reverse-path-tlv">.
</xref>
</t>
</list>
</t>
</section>
</section>
<section anchor="use-case" title="Use Case Scenario">
<t>
In network presented in <xref target="use-case-fig"/> node A monitors two
tunnels to node H: A-B-C-D-G-H and A-B-E-F-G-H.
To bootstrap BFD session to monitor the first tunnel, node A MUST include
BFD Discriminator TLV with Discriminator value foobar-1 and MAY include
BFD Reverse Path TLV that references H-G-D-C-B-A tunnel. To bootstrap
BFD session to monitor the second tunnel, node A MUST include
BFD Discriminator TLV with Discriminator value foobar-2 <xref target="I-D.ietf-bfd-rfc5884-clarifications"/> and MAY include
BFD Reverse Path TLV that references H-G-F-E-B-A tunnel.
</t>
<t>
<figure align="left" anchor="use-case-fig"
title="Use Case for BFD Reverse Path TLV">
<artwork><![CDATA[
C---------D
| |
A-------B G-----H
| |
E---------F
]]></artwork>
</figure>
</t>
<t>
If an operator needs node H to monitor path to node A, e.g.
H-G-D-C-B-A tunnel, then by looking up list of known Reverse Paths
it MAY find and use existing BFD sessions.
</t>
</section>
<section anchor="iana-consider" title="IANA Considerations">
<section anchor="iana-TLV" title="TLV">
<t>
The IANA is requested to assign a new value for BFD Reverse Path TLV from the "Multiprotocol Label
Switching Architecture (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" registry, "TLVs and
sub-TLVs" sub-registry.
</t>
<texttable anchor="bfdtlv-table" title="New BFD Reverse Type TLV">
<ttcol align='left'>Value</ttcol>
<ttcol align='left'>Description</ttcol>
<ttcol align='left'>Reference</ttcol>
<c>X (TBD1)</c>
<c>BFD Reverse Path TLV</c>
<c>This document</c>
</texttable>
</section>
<section anchor="iana-sub-TLV" title="Sub-TLV">
<t>
The IANA is requested to assign two new sub-TLV types from "Multiprotocol Label Switching Architecture (MPLS)
Label Switched Paths (LSPs) Ping Parameters - TLVs" registry, "Sub-TLVs for TLV Types 1, 16, and 21" sub-registry.
</t>
<texttable anchor="spring-sub-tlv-table" title="New Segment Routing Tunnel sub-TLV">
<ttcol align='left'>Value</ttcol>
<ttcol align='left'>Description</ttcol>
<ttcol align='left'>Reference</ttcol>
<c>X (TBD2)</c>
<c>Segment Routing MPLS Tunnel sub-TLV</c>
<c>This document</c>
<c>X (TBD3)</c>
<c>Segment Routing IPv6 Tunnel sub-TLV</c>
<c>This document</c>
</texttable>
</section>
<section anchor="iana-return-code" title="Return Codes">
<t>
The IANA is requested to assign a new Return Code value from the "Multi-Protocol Label Switching (MPLS)
Label Switched Paths (LSPs) Ping Parameters" registry, "Return Codes" sub-registry, as follows using a
Standards Action value.
</t>
<texttable anchor="return-code" title="New Return Code">
<ttcol align='left'>Value</ttcol>
<ttcol align='left'>Description</ttcol>
<ttcol align='left'>Reference</ttcol>
<c>X (TBD4)</c>
<c>Failed to establish the BFD session. The specified reverse path was not found.</c>
<c>This document</c>
</texttable>
</section>
</section>
<section anchor="security" title="Security Considerations">
<t>
Security considerations discussed in <xref target="RFC5880"/>, <xref target="RFC5884"/>, and <xref target="RFC4379"/>, apply to this document.
</t>
</section>
<section title="Acknowledgements">
<t>
</t>
</section>
</middle>
<back>
<references title="Normative References">
&RFC2119;
&RFC5880;
&RFC5881;
&RFC5883;
&RFC5884;
&RFC4379;
&RFC7110;
&RFC5586;
<?rfc include='reference.I-D.kumarkini-mpls-spring-lsp-ping'?>
<?rfc include='reference.I-D.previdi-6man-segment-routing-header'?>
<?rfc include='reference.I-D.ietf-bfd-rfc5884-clarifications'?>
</references>
</back>
</rfc>
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