zebra, bgpd: EVPN VXLAN Multihome support with extern mode

[mrinmoyg]

Introduction of "--kernel-ext-learn" mode of operation in zebra.
This delivers a comprehensive set of enhancements and fixes to support and validate EVPN VXLAN multihoming in external learning mode.

EVPN Multihoming External Mode Support:

• New option as "--kernel-ext-learn" in zebra startup.
• Both data plane and control plane MACs are marked with extern_learn, to prevent kernel aging.
• With the new 'protocol' field in bridge fdb, hardware learnt ('hw') and control plane learnt('zebra') are differentiated.
• 'extern_mode' handling of netlink messaging to debounce 'zebra' protocol messages and accept 'hw' mode for data plane learnt MAC
• 'ARP Suppression' presently not supported for 'extern only' mode of operation
• Specific handling of Sync MAC Update, Delete in extern mode as there is no kernel aging and thereby explicit cleanup is necessary.

Test Enhancements and New Scenarios:
The test framework is updated to cover EVPN VXLAN multihoming with both L2VNI and L3VNI, specifically targeting external learning mode. This includes new logic to handle and verify the correct operation of Ethernet Segments (ES), Designated Forwarder (DF) election, and VTEP peer relationships.
Added and updated topotests under bgp_evpn_mh_l2l3vni_ext_learn to: Validate correct ES discovery and advertisement for both local and remote PEs. Check VTEP peer lists for accuracy, including handling of downed VTEPs and ES state transitions. Ensure L2VNI and L3VNI are correctly instantiated and associated with the appropriate VRFs and VXLAN interfaces. Test orphaned hosts, dual-attached hosts, and single-attached hosts in various failure and recovery scenarios. Utility and Parser Functions:
Utility functions in lib/bgp_evpn.py(new) is added, such as a parser for the show evpn vni json command. This parser extracts VNI-to-type mappings, simplifying validation of VNI configuration and type (L2/L3) in automated tests. These changes adds the test coverage and reliability for EVPN VXLAN multihoming in external mode, making it easier to detect regressions and validate new features.

Per File change summary:

• bgpd/bgp_evpn.c:
  Addition of flog_err for error in installation of VNI MAC and IP to zebra. Non functional.

• include/linux/rtnetlink.h:
  RTPROT_HW definition as 'protocol' in bridge fdb

• zebra/debug_nl.c:
  Updated Netlink print infra to include 'protocol' field in netlink msg dump

• zebra/main.c:
  Add option '--kernel-ext-learn' in zebra startup.

• zebra/rt_netlink.c:
  Debounce/Accept MAC update from kernel based on 'protocol' field (i.e NDA_PROTOCOL)
  Add ext_flags e.g NTF_E_MH_PEER_SYNC as Peer Sync for 'extern_only' mode.
  Add NTF_EXT_LEARNED flag for MAC in dplane programming, also drop for netlink messages from kernel without the flag

• zebra/zebra_evpn.c:
  ARP ND Suppression 'set' and 'get' function definition

• zebra/zebra_evpn.h:
  Corresponding, ARP ND Suppression 'set' and 'get' function declaration

• zebra/zebra_evpn_mac.c:
  zebra_evpn_sync_mac_dp_install: For Sync MAC DPLANE installation, make sure the MAC is inactive for extern mode
  In zebra_evpn_mac_hold_exp_cb: In extern only mode, explicit flush of the mac is required
  In zebra_evpn_sync_mac_del: In extern mode, only reprogram MACif it does not have any PEER flags or neighbor and LOCAL INACTIVE. This helps to clear up the "static" for PEER_PROXY on proxy withdrawal

• zebra/zebra_evpn_mh.c:
  ES Info Set: In extern only mode, use the API zebra_evpn_es_bypass_update_macs to clean MAC from interfaces and ES

• zebra/zebra_evpn_mh.h:
  Declare API zebra_evpn_flush_local_mac as its used in zebra_evpn_mac.c for hold timer expiry cleanup and sync delete of MAC

• zebra/zebra_evpn_neigh.c:
  Prevent neighbor entry installation n DPLANE for remote neighbor if ARP/ND suppression is not enabled. For Extern only mode, ARP/ND Supression is not enabled

• zebra/zebra_router.c:
  For extern only mode, disable ARP suppression

• zebra/zebra_router.h:
  new bool field 'kernel_ext_learn' in zebra_router, to store extern only mode

• zebra/zebra_vxlan.c:
  Add print for EVPN ARP/ND Suppression in "show evpn"

• zebra/zebra_vxlan.h:
  Accessor for Extern Only mode i.e zebra_mac_ext_learn_mode

Review for Kernel Change for Protocol field Addition: https://lore.kernel.org/netdev/[email protected]/T/#u
Review for iproute2 change for protocol field Addition: https://lore.kernel.org/netdev/[email protected]/T/#u

[donaldsharp]

This commit needs to be broken up into small logical units of work such that a reviewer can look at it and understand the logical steps that get you to this new feature. I have given some suggestions on how to do this already. I am sure that there are other places it can be broken up some.

Additionally I see no documentation at all. This needs to be added too. I can review further once this is broken up

[mrinmoyg]

This commit needs to be broken up into small logical units of work such that a reviewer can look at it and understand the logical steps that get you to this new feature. I have given some suggestions on how to do this already. I am sure that there are other places it can be broken up some.

Additionally I see no documentation at all. This needs to be added too. I can review further once this is broken up

Its broken down now, with the zebra.rst file updated for the documentation on the new option.