| Internet-Draft | microTap segment | March 2023 |
| Zhang, et al. | Expires 14 September 2023 | [Page] |
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.¶
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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.¶
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:¶
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.¶
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.¶
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.¶
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).¶
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]:¶
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.¶
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:¶
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| | | | | | | |T |
+--+--+--+--+--+--+--+--+
¶
ISIS signaling is similar to OSPF, as specified in the following sections.¶
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]:¶
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.¶
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:¶
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| | | | | | | |T |
+--+--+--+--+--+--+--+--+
¶
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.¶
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.¶
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.¶
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).¶
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]:¶
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.¶
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.¶
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.¶
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:¶
If a node does not support microtapping but does recognize the microtap SID signaling, the forwarding behavior for the SID is simply pop on that node. This is to safeguard the situation in case the node received a packet with the active SID being a 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.¶
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.¶
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:¶
It is RECOMMENDED that all nodes that perform microtap packet replication be Time of Day (ToD) synchronized via Precision Time Protocol (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.¶
If MTU is a concern, the original label stack (except the microTap SID) and extension headers MAY be removed.¶
To be added.¶
To be added.¶
The following also contributed to this documdent:¶
Peter Van Oene Juniper Networks pvanoene@juniper.net¶