spring Z. Zhang
Internet-Draft Juniper Networks
Intended status: Standards Track R. Hoffman
Expires: 27 April 2023 G. Bajwa
TELUS
D. Voyer
Bell Canada
S. Zadok
Broadcom
24 October 2022
MicroTap Segment in Segment Routing
draft-zzhang-spring-microtap-segment-00
Abstract
This document specifies a microTap segment that can be used to
instruct a transit node to make a copy of a segment-routed packet and
deliver it to a specified node for the purpose of network monitoring,
trouble shooting, or lawful intercept.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://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
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 27 April 2023.
Copyright Notice
Copyright (c) 2022 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 (https://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
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and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Signaling . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1. OSPF Signaling . . . . . . . . . . . . . . . . . . . 4
2.1.2. ISIS Signaling . . . . . . . . . . . . . . . . . . . 6
2.1.3. BGP Signaling . . . . . . . . . . . . . . . . . . . . 8
2.2. Controller Signaling . . . . . . . . . . . . . . . . . . 9
2.2.1. BGP-LS . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.2. PCEP . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.1. Optional IOM header . . . . . . . . . . . . . . . . . 12
3. Security Considerations . . . . . . . . . . . . . . . . . . . 13
4. IANA Assignments . . . . . . . . . . . . . . . . . . . . . . 13
5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. Normative References . . . . . . . . . . . . . . . . . . 13
6.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
Network operators may for various reasons benefit from the ability to
tap packets at strategic locations within their respective networks.
Segment routing [RFC8402] technology offers the ability to both
simplify and improve the operational experience of deploying targeted
packet tapping.
The tapping can be only for some random packets for monitoring
purposes, so we use the term microTap and tap interchangeably in this
document.
The introduction and strategic placement within a SID-list of one or
more microTap SIDs can signal the desire to tap traffic at targeted
points within the network without the need for explicit configuration
on those nodes.
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Consider an SR network in the following example diagram where traffic
is steered along some paths by using a SID-list in the packets. For
network debugging/monitoring purposes, the operator may at any time
want for a certain node (e.g., R2 or R3) in the network to tap a copy
of a packet to a monitor (e.g. connected to R6), while continue to
forward the original packet along its path to the destination.
--R5---R6---monitor
/ /
/ /
src---R1---R2---R3---R4---dst
^ ^
| |
microTap node 1 microTap node 2
To make it very flexible and precise on specifying which packets to
tap on what node and avoid the need to configure filters on the
microTap node, a microTap SID can be inserted to the SID-list after a
Node-SID (for the microTap node) or an Adjacency-SID (that leads to
the microTap node). When the microTap SID becomes the current active
SID, the node does the following:
* Replicate the packet, and send the copy to the remote monitor
* Pop the microTap SID off the original packet and continue
forwarding
There could be multiple monitors. A microTap SID is associated with
a particular monitor (vs. a microTap node). In the above example,
there could be another monitor attached to R5. In that case, there
would be two microTap SIDs - one for the monitor attached at R5 (say
microTap SID S5) and one for the monitor attached at R6 (say microTap
SID S6). The monitor could be a separate server attached to an
interface on R5 or R6, or could be an internal service entity on R5
or R6 (which can be viewed as connected via an internal interface).
If S5 becomes the active SID in a packet arriving at R2, R2 will tap
the packet to R5, by imposing R5's node SID label on top of S5. When
the tapped copy arrives at R5, R5 knows that the packet should be
sent to the internal or external monitor (because S5, which R5
advertises, becomes the active SID). Similarly, if S6 becomes the
active SID in a packet arriving at R3, R3 will tap the packet to R6,
by imposing R6's node SID label on top of S6. In case of SRv6, a
separate IPv6 header is used to send the packet to the router to
which the monitor is attached.
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A microTap SID is advertised by the router that hosts the monitor.
It should only become the active SID in a packet arriving at the
desired microTap node or the advertising/owning node. A node
supporting microTap functionality advertises its ability to do so, so
that incapable nodes will never see a microTap SID as the active SID
in a packet.
The SID-list may contain multiple microTap SIDs that may or may not
be adjacent in the list. For nonadjacent microTap SIDs, different
nodes will tap to the same or different monitors (depending on the
value of microTap SIDs). For adjacent microTap SIDs in the list,
they are likely for different monitors - for the "continue
forwarding" part of the first microTap SID, the second microTap SID
becomes active segment, leading to the second microTap operation.
2. Specification
2.1. Signaling
A node (e.g. R2/R3) supporting microTap function advertise its
capability to other nodes.
A node (e.g. R5/R6) hosting a monitor is provisioned with a microTap
SID allocated from the SRGB. The microTap SID is advertised to other
nodes.
A microTap SID MUST be associated with only one specific monitor.
If the same microTap SID value is advertised by more than one node,
it MUST be treated by a receiving node as an error and ignored, and
MUST NOT be used in the SID-List of a packet.
SRv6 related signaling details will be added in future revisions.
2.1.1. OSPF Signaling
This document defines a new TLV for the advertisement of a microTap
SID (from a node hosting a monitor) and an existing TLV is leverged
for the advertisement of tapping capability (from a microTap node).
2.1.1.1. MicroTap-SID TLV
The microTap SID is advertised in a newly defined MicroTap-SID Sub-
TLV that mimics the Prefix SID Sub-TLV as defined in Section 5 of
[RFC8665]:
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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 | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: To be assigned by IANA
Length: 7 or 8 octets depending on the size of SID (see below).
Flags: Single-octet field. Currently no flags are defined.
Reserved: SHOULD be set to 0 on transmission and MUST be ignored
on reception
MT-ID: Multi-Topology ID (as defined in [RFC4915])
Algorithm: Single octet identifying the algorithm the Prefix-SID
is associated with as defined in Section 3.1
A router receiving a Prefix-SID from a remote node and with an
algorithm value that the remote node has not advertised in the
SR-Algorithm TLV (Section 3.1) MUST ignore the Prefix-SID Sub-
TLV.
SID/Index/Label: Currently a 4-octet index defining the offset
in the Segment Routing Global Block (SRGB) advertised by
this router. In the future the flags field may change
the definition of this definition of this field.
The MicroTap-SID Sub-TLV MAY appear where a Prefix-SID Sub-TLV is
included to advertises a node SID.
2.1.1.2. MicroTap Capability
A new flag T in the Flags field of the Prefix/Adjacency-SID Sub-TLV
indicates that a MicroTap SID is allowed to follow the prefix/
adjacency SID in a packet:
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0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| | | | | | | |T |
+--+--+--+--+--+--+--+--+
2.1.2. ISIS Signaling
ISIS signaling is similar to OSPF, as specified in the following
sections.
2.1.2.1. MicroTap-SID
The microTap SID is advertised in a newly defined MicroTap-SID Sub-
TLV that mimics the Prefix SID Sub-TLV as defined in Section 2.1 of
[RFC8667]:
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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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: To be assigned by IANA.
Length: 5 or 6 depending on the size of the SID (described below)
Flags: 1-octet field. Currently no flags are defined.
Algorithm: the router may use various algorithms when calculating
reachability to other nodes or to prefixes attached to these
nodes. Algorithm identifiers are defined in Section 3.2.
Examples of these algorithms are metric-based Shortest Path
First (SPF), various sorts of Constrained SPF, etc. The
Algorithm field of the Prefix-SID contains the identifier of
the algorithm the router uses to compute the reachability of
the prefix to which the Prefix-SID is associated.
At origination, the Prefix-SID Algorithm field MUST be set to 0
or any value advertised in the SR-Algorithm sub-TLV.
A router receiving a Prefix-SID from a remote node and with an
algorithm value that such remote node has not advertised in the
SR-Algorithm sub-TLV MUST ignore the Prefix-SID
sub-TLV.
SID/Index/Label: : Currently a 4-octet index defining the offset
in the Segment Routing Global Block (SRGB) advertised by
his router. In the future the flags field may change
the definition of this definition of this field.
The MicroTap-SID Sub-TLV MAY appear where a Prefix-SID Sub-TLV is
included to advertises a node SID.
2.1.2.2. Tapping Capability
Similar to OSPF, a new flag T in the Flags field of the Prefix/
Adjacency-SID Sub-TLV indicates that a MicroTap SID is allowed to
follow the prefix/adjacency SID in a packet:
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0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| | | | | | | |T |
+--+--+--+--+--+--+--+--+
2.1.3. BGP Signaling
2.1.3.1. MicroTap-SID
A new MicroTap-SID TLV is defined to advertise a microTap SID. It
has the same encoding as the Label-Index TLV except with a different
type. The following is copied verbatim from [RFC8669]:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Label Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: To be assigned by IANA.
Length: 7, the total length in octets of the value portion of the
TLV.
RESERVED: 8-bit field. It MUST be clear on transmission and MUST
be ignored on reception.
Flags: 16 bits of flags. None are defined by this document. The
Flags field MUST be clear on transmission and MUST be ignored
on reception.
Label Index: 32-bit value representing the index value in the
SRGB space.
A MicroTap-SID TLV MAY be included in the BGP Prefix-SID attribute.
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2.1.3.2. Tapping Capability
A 'T' flag is defined for the existing Originator SRGB TLV's Flags
field to indicate that the originator supports microTapping
functionality. Exact bit position for the flag is to be assigned by
IANA and registered in the "BGP Prefix-SID Originator SRGB TLV Flags"
registry.
2.2. Controller Signaling
A controller needs to know about the nodes (e.g. R2/R3) that support
tapping function, and the nodes (e.g. R5/R6) hosting a monitor &
relavant microTap SID. This information is advertised to the
controller by the link-state routing protocols (ISIS and OSPF) or
BGP-LS. The signaling for OSPF and ISIS has been covered in the
previous sections of this document. This section covers signaling
for BGP-LS and PCEP.
2.2.1. BGP-LS
This document defines a new TLV for the advertisement of a microTap
SID (from a node hosting a monitor) and an existing TLV is leverged
for the advertisement of tapping capability (from a microTap node).
2.2.1.1. MicroTap SID
The microTap SID is advertised in a newly defined MicroTap-SID TLV
that mimics the Prefix SID TLV as defined in Section 2.3.1 of
[RFC9085]:
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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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type: To be assigned by IANA
Length: Variable. 7 or 8 octets depending on the label or index
encoding of the SID.
Flags: 1-octet value that should be set as:
* IS-IS MicroTap-SID flags as defined in Section 2.1.2.1.
* OSPFv2 MicroTap-SID flags as defined in Section 2.1.1.1.
* OSPFv3 MicroTap-SID flags as defined in Section 2.1.1.1.
Algorithm: 1-octet value identifies the algorithm. The semantics of
the algorithm are described in Section 3.1.1 of {{RFC8402}}.
Reserved: 2 octets that MUST be set to 0 and ignored on receipt.
SID/Index/Label:
IS-IS: Label or index value as defined in Section 2.1.2.1.
OSPFv2: Label or index value as defined in Section 2.1.1.1.
OSPFv3: Label or index value as defined in Section 2.1.1.1.
The Flags and, as an extension, the SID/Index/Label fields of this
TLV are interpreted according to the respective underlying IS-IS,
OSPFv2, or OSPFv3 protocol. The Protocol-ID of the BGP-LS Prefix
NLRI is used to determine the underlying protocol specification for
parsing these fields.
The MicroTap-SID TLV MAY appear where a Prefix-SID TLV advertises a
node SID.
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2.2.1.2. Tapping Capability
The Flags of Prefix/Adjacency-SID TLV are interpreted according to
the respective underlying IGP specification. The new flag T in the
Flags field of the Prefix/Adjacency-SID TLV indicates that a MicroTap
SID is allowed to follow the prefix/adjacency SID in a packet.
2.2.2. PCEP
An SR-TE path consists of one or more SIDs and may contain one or
more microTap SIDs. The SR-TE path information is exchanged between
the PCE and PCC in ERO and RRO subobjects. The SR-ERO subobject and
SR-RRO subobject defined in [RFC8664] are used to carry a SID which
can be a microTap SID.
2.3. Procedures
The node hosting a monitor treats a microTap SID that it advertises
as an adjacency SID. In other words, it sets up its forwarding state
for the microTap SID such that packets with the microTap SID as
current active SID will be sent to the monitor (after popping the
microTap SID). It is the responsibility of the monitor to parse the
packet (including the remaining SID-list).
A node supporting microTap functionality sets up its forwarding state
for each microTap SID that it receives, such that packets with the
microTap SID as current active SID are processed as following:
* Make a copy and send it to the advertising node of the microTap
SID. In case of SR-MPLS, this is done by imposing the advertising
node's node SID (optionally after imposing the node SID of the
microTap node so that the monitor knows the microTap node). In
case of SRv6, this is done by imposing an outer IPv6 encapsulation
with the destination address being the advertising node's address.
* Forward the original packet after popping the microTap SID
The ingress node may add microTap SIDs to the SID-list of a packet
based on its monitoring/debugging needs or based on SR policies
programmed from a controller.
A microTap SID MUST not be placed in the SID-list after a node or
adjacency SID that is for or leads to a node that does not advertise
microTap capability. Otherwise, the packet with that SID-list will
be discarded by the node.
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In case of SRv6, the microTap SID and its preceding node SID MAY be
merged into a single IPv6 address in SRH: the locator part identifies
the microTap SID and the function part is the 3-octet or 4-octet
microTap SID.
2.3.1. Optional IOM header
As replicated packets traverse the network from the microtap node to
the monitor nodes, packet loss, packet reordering and buffering can
occur. To allow packet analysis equipment that receives these
replicated packets to accurately analyze the replicated packet flow,
additional information is needed in the replicated packet header to
recreate the original conditions of the flow.
RFC9197] defines a header with data fields well suited for this
purpose. IOAM includes timestamp data, indicating the arrival time
the replicated packet was received at the microtap node. This
timestamp can be used to reproduce accurate inter-packet gaps during
packet analysis. IOAM also includes a sequence number, indicating
the order of replicated packets received by the microtap node. This
sequence number can be used by the packet analysis equipment to
reorder packets, remove duplicated packets, and to alarm on the
condition that replicated packets were lost in transit.
The microTap node MAY include an IOAM header in the replicated packet
with following fields:
* Timestamp Seconds
* Timestamp Fraction
* 64-bit sequence number
It is RECOMMENDED that all nodes that perform microtap packet
replication be ToD synchronized with PTP for the most accurate
recreation of packet conditions during analysis.
The added IOAM header is Edge-to-Edge Option-Type, and in addition to
possible IOAM header already present when the packet arrives at the
microtap node. In case of MPLS, the added IOAM header is an MPLS
extension header [I-D.song-mpls-extension-header] that follows the
Node SID of the node that originated the microtap SID. The extension
header is followed by the original label stack and its OUL field
(Original Upper Layer protocol type) MUST be set to MPLS. In other
words, there may be two label stacks in the packet arriving at the
node hosting the monitoring station.
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If MTU is a concern, the original label stack (except the microTap
SID) and extension headers MAY be removed.
3. Security Considerations
To be added.
4. IANA Assignments
To be added.
5. Contributors
The following also contributed to this documdent:
Peter Van Oene
Juniper Networks
pvanoene@juniper.net
6. References
6.1. Normative References
[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>.
[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>.
[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>.
[RFC8669] Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah,
A., and H. Gredler, "Segment Routing Prefix Segment
Identifier Extensions for BGP", RFC 8669,
DOI 10.17487/RFC8669, December 2019,
<https://www.rfc-editor.org/info/rfc8669>.
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[RFC9085] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
H., and M. Chen, "Border Gateway Protocol - Link State
(BGP-LS) Extensions for Segment Routing", RFC 9085,
DOI 10.17487/RFC9085, August 2021,
<https://www.rfc-editor.org/info/rfc9085>.
6.2. Informative References
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
[]
Song, H., Zhou, T., Andersson, L., Zhang, Z. J., and R.
Gandhi, "MPLS Network Actions using Post-Stack Extension
Headers", Work in Progress, Internet-Draft, draft-song-
mpls-extension-header-11, 15 October 2022,
<https://www.ietf.org/archive/id/draft-song-mpls-
extension-header-11.txt>.
Authors' Addresses
Zhaohui Zhang
Juniper Networks
Email: zzhang@juniper.net
Ryan Hoffman
TELUS
Email: ryan.hoffman@telus.com
Gurminderjit Bajwa
TELUS
Email: gurminderjit.bajwa@telus.com
Daniel Voyer
Bell Canada
Email: daniel.voyer@bell.ca
Shay Zadok
Broadcom
Email: shay.zadok@broadcom.com
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