SRv6 uSID (micro-SID) support for traffic flow packet headers (RFC 9800)

[SuryyaKrJana]

Feature Overview

• Related Issue: (e.g., Fixes #<issue_number>)

• Brief Description:
  SRv6 uSID (micro-SID) support for traffic flow packet headers (RFC 9800)

• Two new encoding paths are added to allow traffic generation with SRv6 uSID compressed segment identifiers:

• No-SRH reduced encapsulation (ipv6.yaml): new dst_usids field on the IPv6 header (Flow.Ipv6.UsidDst) — packs a locator block + ordered uSID list directly into the 128-bit IPv6 dst with no Segment Routing Header. For paths that fit in a single uSID container (e.g. F3216: locator /32 + up to 6 × 16-bit uSIDs).

• SRH-based uSID encapsulation (ipv6_routing.yaml): new segment_routing_usid choice on Flow.Ipv6Routing (Flow.Ipv6SegmentRoutingUsid) — carries multiple compressed uSID containers in an SRH segment list for multi-hop paths that exceed one container.

• Supporting additions: shared Flow.Ipv6SRH.PadTlv schema (optional SRH padding TLV for 8-byte alignment), OAM flag support (Flow.Ipv6SegmentRouting.uSidFlags), and description/path-depth fixes across the existing SR-MPLS IS-IS device schemas.

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Feature Details

• Redocly docs for this feature/branch

• New Locations/Nomenclature:
  Specify where new attributes/nodes have been added in the models hierarchy to allow viewers to quickly navigate to the correct areas in the generated Redocly view corresponding to the model change.

• Dev-Snappi branch reference

• Example command to fetch the srv6-raw-traffic

  go get github.com/open-traffic-generator/snappi/gosnappi@<srv6-raw-traffic>
  

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Code snippets

Code snippets

Example - 1: Multiple uSIDs with NO SRH: 3-hop path packed into one F3216 uSID container,
placed directly in the IPv6 destination via ipv6.dst_usids - no routing extension
header required.
OTG model used:
Flow.Ipv6 (dst = uSID container, NH auto-set to 17 by next header)
F3216 uSID container layout (128 bits):
fc00:0:1:2:3::
Locator-Block = fc00:0000 (32 bits, shared domain prefix)
uSID-1 = 0001 (16 bits, hop 1 - egress of node 1)
uSID-2 = 0002 (16 bits, hop 2 - egress of node 2)
uSID-3 = 0003 (16 bits, hop 3 - egress of node 3)
Remaining = 0:: (48 bits, zeros = end of uSID list)

 #  USID creation without helper API
    .......................
     .........................
    f.tx_rx.port.tx_name = p1.name
    f.tx_rx.port.rx_name = p2.name
   
    eth = f.packet.add().ethernet
    eth.src.value = "00:11:22:33:44:55"
    eth.dst.value = "00:aa:bb:cc:dd:ee"

    ip6 = f.packet.add().ipv6
    ip6.src.value = "2001:db8::1"
    du = ip6.dst_usids
    du.locator.value = "fc00::"
    du.locator_length.value = 32
    du.usids = ["0001", "0002", "0003"]
   

Example - 2: Multiple uSIDs with 1 uSID SRH container: 3-hop path packed in one F3216 uSID
container, carried inside a uSID SRH extension header with a single segment entry.

OTG model used:
Flow.Ipv6 (NH=43, dst = uSID container)
Flow.Ipv6ExtHeader.routing.segment_routing_usid (Flow.Ipv6SegmentRoutingUsid)
segment_list: 1 entry (last_entry=0, segments_left=0)

F3216 uSID container layout (128 bits):
fc00:0:1:2:3::
Locator-Block = fc00:0000 (32 bits, shared domain prefix)
uSID-1 = 0001 (16 bits, hop 1)
uSID-2 = 0002 (16 bits, hop 2)
uSID-3 = 0003 (16 bits, hop 3)
Remaining = 0:: (48 bits, zeros = end of uSID list)

   usid_container = "fc00:0:1:2:3::"
    locator        = "fc00::"
    locator_length = 32
    usids          = ["0001", "0002", "0003"]
    segments_left  = 0
    last_entry     = 0

    f.tx_rx.port.tx_name = p1.name
    f.tx_rx.port.rx_name = p2.name
   
    eth = f.packet.add().ethernet
    eth.src.value = "00:11:22:33:44:55"
    eth.dst.value = "00:aa:bb:cc:dd:ee"

    ip6 = f.packet.add().ipv6
    ip6.src.value = "2001:db8::1"
    du = ip6.dst_usids
    du.locator.value        = locator
    du.locator_length.value = locator_length
    du.usids                = list(usids)
    ip6.next_header.value = 43

    usid = f.packet.add().ipv6_extension_header.routing.segment_routing_usid
    usid.segments_left.value = segments_left
    usid.last_entry.value    = last_entry
    usid.tag.value           = 0

    seg = usid.segment_list.segment()[-1]
    seg.locator.value        = locator
    seg.locator_length.value = locator_length
    seg.usids                = list(usids)

Example 3: Multiple uSIDs with more than 1 uSID SRH container: 4-hop path spread across
2 F3216 uSID containers, carried in a uSID SRH with 2 segment list entries.

OTG model used:
Flow.Ipv6 (NH=43, dst assembled from dst_usids)
Flow.Ipv6ExtHeader.routing.segment_routing_usid
segment_list: 2 entries (last_entry=1, segments_left=1)
segment[0]:
locator.value = "fc00::"
locator_length.value = 32
usids = ["0001", "0002"]
segment[1]:
locator.value = "fc00::"
locator_length.value = 32
usids = ["0003", "0004"]

   locator        = "fc00::"
    locator_length = 32
    container1     = "fc00:0:1:2::"
    usids_c1       = ["0001", "0002"]
    container2     = "fc00:0:3:4::"
    usids_c2       = ["0003", "0004"]
    segments_left  = 1
    last_entry     = 1

    f.tx_rx.port.tx_name = p1.name
    f.tx_rx.port.rx_name = p2.name


    eth = f.packet.add().ethernet
    eth.src.value = "00:11:22:33:44:55"
    eth.dst.value = "00:aa:bb:cc:dd:ee"

    ip6 = f.packet.add().ipv6
    ip6.src.value = "2001:db8::1"
    du = ip6.dst_usids
    du.locator.value        = locator
    du.locator_length.value = locator_length
    du.usids                = list(usids_c1)
    ip6.next_header.value = 43

    usid = f.packet.add().ipv6_extension_header.routing.segment_routing_usid
    usid.segments_left.value = segments_left
    usid.last_entry.value    = last_entry
    usid.tag.value           = 0

    seg0 = usid.segment_list.segment()[-1]
    seg0.locator.value        = locator
    seg0.locator_length.value = locator_length
    seg0.usids                = list(usids_c1)

    seg1 = usid.segment_list.segment()[-1]
    seg1.locator.value        = locator
    seg1.locator_length.value = locator_length
    seg1.usids                = list(usids_c2)

** Example 4: RFC 9800 Figure 5 — REPLACE-CSID Compressed SID List (7 SIDs)**

(REPLACE-CSID flavor). Parameters: LBL=48 bits, LNFL=32 bits, K=4 slots.
Container 1 — outer IPv6 DA (full SRv6 SID, not in SRH):
[Locator-Block (48b) = 2001:db8::] [1st CSID (32b) = 0x00010001] [Arg=0 (48b)]
Assembled DA: 2001:db8:0:1:1::

Container 2 — SRH seg[1] (packed, fully filled, processes CSIDs 2-5):
Packing (usids[i] -> position K-1-i, i.e. usids[0] at LSB bits 96-127):
position 3 (LSB bits 96-127): 2nd CSID = 0x00020002
position 2 (bits 64-95): 3rd CSID = 0x00030003
position 1 (bits 32-63): 4th CSID = 0x00040004
position 0 (MSB bits 0-31): 5th CSID = 0x00050005
Wire (MSB->LSB): [00050005][00040004][00030003][00020002]
IPv6: 5:5:4:4:3:3:2:2

Container 3 — SRH seg[0] (packed, partially filled, processes CSIDs 6-7):
Packing:
position 3 (LSB bits 96-127): 6th CSID = 0x00060006
position 2 (bits 64-95): 7th CSID = 0x00070007
positions 1, 0 (MSB end): zeros (end-of-CSID-list padding)
Wire (MSB->LSB): [00000000][00000000][00070007][00060006]
IPv6: ::7:7:6:6
SRH: last_entry=1 (2 entries: seg[0] and seg[1]), segments_left=1.

    # Container 1: REPLACE-CSID first SID in outer IPv6 DA via dst_usids.
    # LBL=48 (2001:0db8:0000), LNFL=32, CSID1=0x00010001, Arg=0 -> 2001:db8:0:1:1::
    active_dst        = "2001:db8:0:1:1::"
    da_locator        = "2001:db8::"
    da_locator_length = 48
    da_usids          = ["00010001"]
    segments_left = 1
    last_entry    = 1

    # Container 3 — seg[0] (last entry in SRH; CSIDs 6-7, 2 of K=4 slots used).
    # Exactly K=4 CSIDs: slots 0-1 zero, usids[2]=CSID-7, usids[3]=CSID-6 (LSB, first processed).
    # Wire: [00000000][00000000][00070007][00060006] = ::7:7:6:6
    csids_seg0    = ["00000000", "00000000", "00070007", "00060006"]

    # Container 2 — seg[1] (second entry; CSIDs 2-5, all K=4 slots used).
    # Exactly K=4 CSIDs: usids[0]=CSID-5 (MSB), usids[3]=CSID-2 (LSB, first processed).
    # Wire: [00050005][00040004][00030003][00020002] = 5:5:4:4:3:3:2:2
    csids_seg1    = ["00050005", "00040004", "00030003", "00020002"]

    f.tx_rx.port.tx_name = p1.name
    f.tx_rx.port.rx_name = p2.name
 
    eth = f.packet.add().ethernet
    eth.src.value = "00:11:22:33:44:55"
    eth.dst.value = "00:aa:bb:cc:dd:ee"

    # Outer IPv6: DA = container 1 assembled from dst_usids.
    ip6 = f.packet.add().ipv6
    ip6.src.value = "2001:db8::1"
    du = ip6.dst_usids
    du.locator.value        = da_locator
    du.locator_length.value = da_locator_length
    du.usids                = list(da_usids)
    ip6.next_header.value = 43

    # REPLACE-CSID SRH: 2 packed containers (locator_length=0 = packed format).
    usid_hdr = f.packet.add().ipv6_extension_header.routing.segment_routing_usid
    usid_hdr.segments_left.value = segments_left
    usid_hdr.last_entry.value    = last_entry
    usid_hdr.flags.oam.value     = 0
    usid_hdr.tag.value           = 0

    # seg[0] added first => index 0 in segment_list = last SRH entry (CSIDs 6-7).
    seg0 = usid_hdr.segment_list.segment()[-1]
    seg0.locator.value        = "::0"
    seg0.locator_length.value = 0
    seg0.usids                = list(csids_seg0)

    # seg[1] added second => index 1 in segment_list (CSIDs 2-5, fully packed).
    seg1 = usid_hdr.segment_list.segment()[-1]
    seg1.locator.value        = "::0"
    seg1.locator_length.value = 0
    seg1.usids                = list(csids_seg1)

[apratimmukherjee]

Some cleanup is needed.
Main issue : Need to decide on array of hex vs array of object with usid (hex )