Support for ISIS SRv6 as per RFC9352

[SuryyaKrJana]

Feature Overview

• Related Issue: (e.g., Fixes #<issue_number>)
• Brief Description:
  Support of ISIS SRv6 Capabilities, Node SIDs and Adjacency SIDs in OTG-Model and Snappi-IxNetwork

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Feature Details

• Redocly docs for this feature

• New Locations/Nomenclature:

• ISIS SRv6 Reference: RFC 9352
  isis.segment_routing.
  isis.interfaces.srv6_adjacency_sids

• Dev-Snappi branch reference

• Example command to fetch the dev-snappi branch:

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

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Code snippets

Control plane:
r1 (Port 1): locator fc00:0:1::/48, End SID fc00:0:1:1:: (behavior=End, code=1)
r2 (Port 2): locator fc00:0:2::/48, End SID fc00:0:2:1:: (behavior=End, code=1)
Both adjacencies (r1↔DUT, r2↔DUT) must form; DUT re-floods LSPs.
Wire: r1's LSP (re-flooded by DUT) and r2's own LSP both captured on p2.

Data plane (device-based, via DUT):
tx=d1_v6, rx=d2_v6 — IxN resolves DUT MAC via NDP automatically
Outer IPv6 src=2001:0:1::1 dst=fc00:0:10:1:: (DUT End SID) nh=43
SRH: routing_type=4, segments_left=1, last_entry=1
seg[0]=fc00:0:2:1:: seg[1]=fc00:0:10:1::
Inner: IPv4 TCP src=10.1.1.1 dst=10.2.2.2 sport=1234 dport=80
DUT End processing: sl 1→0, outer dst→fc00:0:2:1::, forwarded to p2.

 # ---- Devices and Ethernet ------------------------------------------------
# p1 and p2 face DIFFERENT DUT interfaces — each is on its own /64 subnet.
    # d1 (p1 side): IxN=2001:0:1::1, DUT port-1=2001:0:1::2
    # d2 (p2 side): IxN=2001:0:2::1, DUT port-2=2001:0:2::2
    DUT_END_SID     = "fc00:0:10:1::"      # DUT End SID — update to match DUT IS-IS SRv6 config.
    d1_eth                      = d1.ethernets.add()
    d1_eth.name                 = "d1_eth"
    d1_eth.connection.port_name = p1.name
    d1_eth.mac                  = "00:00:00:01:01:01"
    d1_v6         = d1_eth.ipv6_addresses.add()
    d1_v6.name    = "d1_ipv6"
    d1_v6.address = "2001:0:1::1"   # IxN port-1 address
    d1_v6.gateway = "2001:0:1::2"   # DUT interface connected to port 1
    d1_v6.prefix  = 64

    d2_eth                      = d2.ethernets.add()
    d2_eth.name                 = "d2_eth"
    d2_eth.connection.port_name = p2.name
    d2_eth.mac                  = "00:00:00:02:02:02"
    d2_v6         = d2_eth.ipv6_addresses.add()
    d2_v6.name    = "d2_ipv6"
    d2_v6.address = "2001:0:2::1"   # IxN port-2 address
    d2_v6.gateway = "2001:0:2::2"   # DUT interface connected to port 2
    d2_v6.prefix  = 64

    # ---- IS-IS router r1 — Port 1 ↔ DUT -------------------------------------
    r1                              = d1.isis
    r1.name                         = "r1"
    r1.system_id                    = "650000000001"
    r1.advanced.area_addresses      = ["490001"]
   
    r1_intf                                          = r1.interfaces.add()
    r1_intf.eth_name                                 = "d1_eth"
    r1_intf.name                                     = "r1_intf"
    r1_intf.network_type                             = "point_to_point"
    r1_intf.level_type                               = "level_2"
   
    r1.segment_routing.router_capability.srv6_capability.c_flag = True
    r1_loc                                              = r1.segment_routing.srv6_locators.add()
    r1_loc.locator_name                                 = "loc1"
    r1_loc.locator                                      = "fc00:0:1::"
    r1_loc.prefix_length                                = 48
    r1_loc.algorithm                                    = 0
    r1_loc.metric                                       = 10
    r1_loc.d_flag                                       = False
    r1_loc.sid_structure.locator_block_length           = 32
    r1_loc.sid_structure.locator_node_length            = 16
    r1_loc.sid_structure.function_length                = 16
    r1_loc.sid_structure.argument_length                = 0
    r1_loc.advertise_locator_as_prefix.route_metric     = 10
    r1_loc.advertise_locator_as_prefix.redistribution_type = "up"
    r1_loc.advertise_locator_as_prefix.route_origin    = "internal"

    r1_sid                    = r1_loc.end_sids.add()   # fc00:0:1:1:: End (code 1)
    r1_sid.function           = "0001"
    r1_sid.argument           = "0000"
    r1_sid.endpoint_behavior  = "end"
    r1_sid.c_flag             = True

    r1_routes         = r1.v6_routes.add()
    r1_routes.name    = "r1_v6_routes"
    r1_addr           = r1_routes.addresses.add()
    r1_addr.address   = "fd00:0:1::1"
    r1_addr.prefix    = 64
    r1_addr.count     = 1

    # ---- IS-IS router r2 — Port 2 ↔ DUT -------------------------------------
    r2                              = d2.isis
    r2.name                         = "r2"
    r2.system_id                    = "650000000002"
    r2.advanced.area_addresses      = ["490001"]
   
    r2_intf                                          = r2.interfaces.add()
    r2_intf.eth_name                                 = "d2_eth"
    r2_intf.name                                     = "r2_intf"
    r2_intf.network_type                             = "point_to_point"
    r2_intf.level_type                               = "level_2"

    r2.segment_routing.router_capability.srv6_capability.c_flag = True
    r2_loc                                            = r2.segment_routing.srv6_locators.add()
    r2_loc.locator_name                      = "loc2"
    r2_loc.locator                                 = "fc00:0:2::"
    r2_loc.prefix_length                                = 48
    r2_loc.algorithm                                    = 0
    r2_loc.metric                                       = 10
    r2_loc.d_flag                                       = False
    r2_loc.sid_structure.locator_block_length           = 32
    r2_loc.sid_structure.locator_node_length            = 16
    r2_loc.sid_structure.function_length                = 16
    r2_loc.sid_structure.argument_length                = 0
    r2_loc.advertise_locator_as_prefix.route_metric     = 10
    r2_loc.advertise_locator_as_prefix.redistribution_type = "up"
    r2_loc.advertise_locator_as_prefix.route_origin    = "internal"

    r2_sid                    = r2_loc.end_sids.add()   # fc00:0:2:1:: End (code 1)
    r2_sid.function           = "0001"
    r2_sid.argument           = "0000"
    r2_sid.endpoint_behavior  = "end"
    r2_sid.c_flag             = True

    r2_routes         = r2.v6_routes.add()
    r2_routes.name    = "r2_v6_routes"
    r2_addr           = r2_routes.addresses.add()
    r2_addr.address   = "fd00:0:2::1"
    r2_addr.prefix    = 64
    r2_addr.count     = 1

    # ---- SRH device-based flow: d1 → DUT → d2 ----------------------------------
    # tx=d1_v6 / rx=d2_v6: IxN resolves the DUT's MAC via NDP (no hardcoded MAC).
    # Outer IPv6 dst = DUT End SID; DUT applies End:
    #   sl 1→0, outer dst ← seg[0] = fc00:0:2:1::, forwards out port 2.
    # Capture on p2 verifies: sl=0, segments unchanged, inner TCP intact.
    f1                                = cfg.flows.add()
    f1.name                           = "srh_pdp1"
    f1.tx_rx.device.tx_names          = [d1_v6.name]
    f1.tx_rx.device.rx_names          = [d2_v6.name]
    f1.rate.pps                       = 100
    f1.duration.fixed_packets.packets = 200
    f1.metrics.enable                 = True

    ip6_1                       = f1.packet.add().ipv6
    ip6_1.src.value             = "2001:0:1::1"
    ip6_1.dst.value             = _DUT_END_SID    # DUT End SID: sl pointer
    ip6_1.next_header.value     = 43              # SRH

    sr1                         = f1.packet.add().ipv6_extension_header.routing.segment_routing
    sr1.segments_left.value     = 1               # points to seg[1] = DUT End SID
    sr1.last_entry.value        = 1               # 2-segment list (0-indexed)
    sr1.flags.protected.value   = 0
    sr1.flags.oam.value         = 0
    sr1.flags.alert.value       = 0
    sr1.tag.value               = 0
    seg                         = sr1.segment_list.segment()[-1]
    seg.segment.value           = "fc00:0:2:1::"  # seg[0]: next hop after DUT
    seg                         = sr1.segment_list.segment()[-1]
    seg.segment.value           = _DUT_END_SID    # seg[1]: DUT End SID (current)

    ip4_inner                   = f1.packet.add().ipv4
    ip4_inner.src.value         = "10.1.1.1"
    ip4_inner.dst.value         = "10.2.2.2"
    ip4_inner.protocol.value    = 6              # TCP

    tcp_inner                   = f1.packet.add().tcp
    tcp_inner.src_port.value    = 1234
    tcp_inner.dst_port.value    = 80

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