Validate end-to-end route propagation across a two-tier BGP routing architecture: Customer Edge (CE) $\leftrightarrow$ Provider Edge Router (DUT) $\leftrightarrow$ Core Route Reflector (RR). Verify full path attribute transparency across boundaries, including preservation of customer Multi-Exit Discriminator (MED), passing of core priority metrics to customer peers via metric-preservation policies, and AS-Path integrity during multiprotocol L3VPN encapsulation.

• TESTBED_DUT_ATE_4LINKS (ATE Port 1 simulating Customer CE1; ATE Port 2 simulating Customer CE2; ATE Port 3 simulating Core Route Reflector RR1; ATE Port 4 simulating Core Route Reflector RR2).

graph LR;
  ce1[ATE Port 1: CE1 (AS 65001)] -- "eBGP (VRF ce1)" --> dut1[DUT Port 1]
  ce2[ATE Port 2: CE2 (AS 65002)] -- "eBGP (VRF ce1)" --> dut2[DUT Port 2]
  dut3[DUT Port 3] -- "iBGP MP-BGP (AS 64500)" --> rr1[ATE Port 3: RR1]
  dut4[DUT Port 4] -- "iBGP MP-BGP (AS 64500)" --> rr2[ATE Port 4: RR2]

1. Configure tenant VRF ce1 on DUT with assigned Route Distinguisher (e.g. 64500:100) and Route Targets (target:64500:100).
2. Establish eBGP peering on DUT Port 1 (192.0.2.1/30) with ATE CE1 (192.0.2.2, AS 65001) in VRF ce1.
3. Establish eBGP peering on DUT Port 2 (192.0.2.5/30) with ATE CE2 (192.0.2.6, AS 65002) in VRF ce1.
4. Establish dynamic or static iBGP peering over IPv6 transit on DUT Port 3/4 with ATE RR1/RR2 in default/transit VRF with vpn-ipv4 and vpn-ipv6 enabled.
5. Apply metric preservation policy on DUT:
   • Ingress eBGP: preserve customer-signaled MED when translating into VPNv4/VPNv6 updates.
   • Egress eBGP: pass received core MED to customer CE via metric preservation policy (set metric +0 or policy-definition set-med).

• Step 1: ATE CE1 advertises IPv4 prefix 198.51.100.0/24 with AS-Path [65001] and IPv6 prefix 2001:db8:10::/64 with AS-Path [65001].
• Step 2: Verify DUT receives routes in VRF ce1 Adj-RIB-In.
• Step 3: Verify DUT encapsulates routes into MP-BGP L3VPN updates and transmits them over iBGP to ATE RR1.
• Step 4: Verify ATE RR1 receives both prefixes with:
  • Preserved AS-Path: [65001].
  • Correct RD: 64500:100.
  • Matching Route Target: target:64500:100.

• Step 1: ATE RR1 advertises core network prefix 203.0.113.0/24 and 2001:db8:250::/64 with RD 64500:100 and RT target:64500:100 to DUT over iBGP.
• Step 2: Verify DUT imports the VPN routes into tenant VRF ce1.
• Step 3: Verify DUT advertises 203.0.113.0/24 and 2001:db8:250::/64 to ATE CE1 over eBGP.
• Step 4: Verify ATE CE1 receives the prefix with DUT's autonomous system (64500) prepended to the AS-Path.

• Step 1: ATE CE1 advertises prefix 198.51.100.0/25 and 2001:db8::cafe/128 with explicit MED = 200.
• Step 2: Query DUT telemetry at /network-instances/network-instance[name=ce1]/protocols/protocol[identifier=openconfig-policy-types:BGP][name=BGP]/bgp/rib/attr-sets/attr-set/state/med (referenced by route entry under /network-instances/network-instance[name=ce1]/protocols/protocol[identifier=openconfig-policy-types:BGP][name=BGP]/bgp/rib/afi-safis/afi-safi[afi-safi-name=openconfig-bgp-types:IPV4_UNICAST]/ipv4-unicast/neighbors/neighbor[neighbor-address=192.0.2.2]/adj-rib-in-post/routes/route/state/attr-index); verify MED value is 200.
• Step 3: Monitor MP-BGP L3VPN update received at ATE RR1; verify the MED attribute value 200 is retained unaltered in the update.

• Step 1: ATE RR1 advertises IPv4 prefix 203.0.113.0/24 and IPv6 prefix 2001:db8:250::/64 with MED = 123 representing core route reflector active/backup priority.
• Step 2: Verify DUT receives MED 123 on the iBGP session for both IPv4 and IPv6 prefixes.
• Step 3: Verify DUT propagates both IPv4 and IPv6 updates to ATE CE1 retaining MED = 123 on the egress eBGP updates (preventing reset to 0).

• Step 1: ATE CE1 advertises prefix 198.51.100.128/25 with AS-Path [65001, 65010].
• Step 2: ATE CE2 advertises the same prefix 198.51.100.128/25 with alternate AS-Path [65002, 65020, 65030].
• Step 3: Verify DUT installs both paths in BGP RIB when BGP multipath/add-path is enabled.
• Step 4: Verify best-path selection favors CE1 (shorter AS-Path length).
• Step 5: Send continuous data plane traffic destined to 198.51.100.128/25 and withdraw the prefix from ATE CE1; validate sub-second cutover to the CE2 path by measuring packet loss and verifying total traffic loss duration is less than 1 second.

{
  "routing-policy": {
    "policy-definitions": {
      "policy-definition": [
        {
          "name": "PRESERVE-MED",
          "config": {
            "name": "PRESERVE-MED"
          }
        },
        {
          "name": "PASS-CORE-MED",
          "config": {
            "name": "PASS-CORE-MED"
          }
        }
      ]
    }
  },
  "network-instances": {
    "network-instance": [
      {
        "name": "ce1",
        "config": {
          "name": "ce1",
          "type": "openconfig-network-instance-types:L3VRF",
          "route-distinguisher": "64500:100"
        },
        "protocols": {
          "protocol": [
            {
              "identifier": "openconfig-policy-types:BGP",
              "name": "BGP",
              "bgp": {
                "global": {
                  "config": {
                    "as": 64500
                  }
                },
                "neighbors": {
                  "neighbor": [
                    {
                      "neighbor-address": "192.0.2.2",
                      "config": {
                        "neighbor-address": "192.0.2.2",
                        "peer-as": 65001
                      },
                      "apply-policy": {
                        "config": {
                          "import-policy": ["PRESERVE-MED"],
                          "export-policy": ["PASS-CORE-MED"]
                        }
                      }
                    }
                  ]
                }
              }
            }
          ]
        }
      }
    ]
  }
}

paths:
  # BGP RIB Attributes and Routes
  /network-instances/network-instance/protocols/protocol/bgp/rib/afi-safis/afi-safi/ipv4-unicast/loc-rib/routes/route/state/prefix:
  /network-instances/network-instance/protocols/protocol/bgp/rib/afi-safis/afi-safi/ipv6-unicast/loc-rib/routes/route/state/prefix:
  /network-instances/network-instance/protocols/protocol/bgp/rib/afi-safis/afi-safi/ipv4-unicast/neighbors/neighbor/adj-rib-in-post/routes/route/state/prefix:
  /network-instances/network-instance/protocols/protocol/bgp/rib/afi-safis/afi-safi/ipv4-unicast/neighbors/neighbor/adj-rib-out-post/routes/route/state/prefix:
  /network-instances/network-instance/protocols/protocol/bgp/rib/attr-sets/attr-set/as-path/as-segment/state/member:
  /network-instances/network-instance/protocols/protocol/bgp/rib/attr-sets/attr-set/state/med:

rpcs:
  gnmi:
    gNMI.Get:
    gNMI.Subscribe:

• FFF