Review TC47/TC49: align test_base_dci_l3vni_external_connectivity with testplan

[bpar9]

Description of PR

Summary:
Reworks test_base_dci_l3vni_external_connectivity (L3VNI_dci:47 IPv4 / L3VNI_dci:49 IPv6) to align with the DCI Solution Testplan specification. The previous implementation deviated from the testplan in several significant ways (peering target, IP addresses, traffic direction, verification depth). This PR addresses 9 identified gaps.

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• New Test case
  • Skipped for non-supported platforms
• Test case improvement

Back port request

• 202205
• 202305
• 202311
• 202405
• 202411
• 202505
• 202511

Approach

What is the motivation for this PR?

The existing test_base_dci_l3vni_external_connectivity had significant deviations from the testplan:

Gap	Severity	Issue
GAP-1	HIGH	Peered with DC1/DC2 leaves instead of a DC1 BGW — bypasses RT-REWRITE and L3VNI Type-5 origination
GAP-4	HIGH	Traffic sourced from DC1 host instead of DC2 host — bypasses cross-DC DCI forwarding path
GAP-6	LOW	Wrong IPs/ASN (21.1.1.x/65333 vs testplan 10.250.1.x/65500)
GAP-2	MEDIUM	Flat st.wait(60) instead of BGP session polling
GAP-3	MEDIUM	Shallow Type-5 check (string match only, no FIB/RIB verification)
GAP-7	MEDIUM	No DCI uplink drop counter checks
GAP-8	MEDIUM	Incomplete cleanup (VRF not deleted, no post-cleanup health check)
GAP-9	LOW	Missing redistribute bgp for Type-5 generation on BGW

How did you do it?

1. Peering target → DC1 BGW: Discovery logic now searches dc1_bgw nodes instead of leaf nodes. DC2 direct peering removed entirely — DC2 learns ext_prefix via EVPN Type-5 over DCI.
2. Traffic source → DC2 host: Stream now originates from a DC2 leaf Ixia port, traversing DC2 leaf → DC2 BGW → DCI → DC1 BGW → external router.
3. IP addresses/ASN aligned: ext_asn=65500, IPv4 10.250.1.x/30 + 10.99.0.0/24, IPv6 2001:db8:250::x/126 + 2001:db8:99::/64.
4. BGP polling: Replaced st.wait(60) with a polling loop (5s × 12 attempts) checking show bgp vrf Vrf101 summary for Established state.
5. Type-5 verification enhanced: Checks DC1 BGW (locally originated), DC2 BGW (received over WAN), DC2 leaf (received from DC2 BGWs), plus VRF FIB installation on DC2 nodes.
6. DCI uplink drop counters: Logs show interfaces counters on DC2 leaf, DC2 BGW, DC1 BGW after traffic.
7. Cleanup improved: Removes route-maps/prefix-lists, deletes VRF on external router, runs verify_base_setup_bgw() post-cleanup.
8. redistribute bgp added on DC1 BGW alongside redistribute connected.

How did you verify/test it?

• Syntax-validated with py_compile (passes).
• Not tested on a live testbed — this requires a multi-DC EVPN-VXLAN fabric with Ixia. Testbed validation is required before merge.

Any platform specific information?

N/A — applies to any SONiC platform supporting EVPN-VXLAN DCI with BGW spines.

Supported testbed topology if it's a new test case?

Not a new test case. Existing 3-DC DCI topology with BGW spines.

⚠️ Items for reviewer attention

1. TGEN IP config may be wrong — The TGEN device group uses ext_prefix_host (e.g. 10.99.0.10) as both gateway and intf_ip_addr. In the old code these were distinct values (tgen_gw_ip vs tgen_host_ip). Verify this is correct for the Ixia emulated host setup, or whether the gateway should be a different IP (e.g., the external router's connected interface in ext_prefix subnet).
2. Drop counter check is log-only — Step 8 logs drop counters but does not fail the test on non-zero drops. The testplan specifies "0 drops." Consider whether this should assert.
3. redistribute bgp — Added per testplan ("if needed"), but could cause unintended redistribution of other BGP-learned routes in Vrf101 on the BGW. Verify this is safe in the DCI base profile.
4. Topology dependency — The test now requires a physical link from a DC1 BGW to the external router. If no such link exists, the test skips. Previously it searched for leaf-to-router links.

Documentation

N/A

Link to Devin session: https://cisco-demo.devinenterprise.com/sessions/1849ed21f9c04ca1a02f8329683d1afd
Requested by: @bpar9

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring