frr-mgmt-framework, YANG: add IPv6 ND/RA support for VLAN_INTERFACE

[zedzean]

Why I did it

There is no ConfigDB-native mechanism to configure IPv6 Neighbor Discovery / Router Advertisement parameters on VLAN interfaces in SONiC today. The only way to apply ipv6 nd suppress-ra, ipv6 nd managed-config-flag, ipv6 nd other-config-flag, or ipv6 nd ra-interval <N> to an SVI is to issue vtysh commands manually, which do not persist and are outside the frrcfgd management framework.

This change aligns with the direction proposed in SONiC HLD #2165 (OpenConfig Interfaces Router Advertisement, targeted at the 202605 release) by adding the three interface-level flag leaves to VLAN_INTERFACE_LIST and implementing the frrcfgd translation to zebra interface-context commands.

A fourth leaf (nd_ra_interval) is added as a SONiC-native extension. It has no OpenConfig mapping in the current HLD but is useful for the common operational case of tuning the unsolicited RA cadence. Reviewers: if you'd
prefer this deferred to a separate PR until it lands in the HLD, please say so and I'll split the patch.

How I did it

YANG (sonic-vlan.yang): added four new leaves to VLAN_INTERFACE_LIST:

Leaf	Type	OpenConfig mapping
nd_suppress_ra	boolean	router-advertisement/config/suppress
nd_managed_config_flag	boolean	router-advertisement/config/managed
nd_other_config_flag	boolean	router-advertisement/config/other-config
nd_ra_interval	uint32 range 1..1800	(none - extension)

A new revision entry was added to the yang file.

frrcfgd (frrcfgd.py): subscribed to the VLAN_INTERFACE table, introduced a vlan_intf_nd_key_map using the standard {no:no-prefix} convention established by PR #21697 (hdl_admin_status style). Interface-context command dispatch follows the existing PIM_INTERFACE / IGMP_INTERFACE pattern.

DELETE semantics restore per-flag FRR defaults rather than blindly emitting no <cmd>. Two handler variants make this explicit:
hdl_nd_flag_default_on (used for suppress-ra whose FRR default is enabled on non-P2P interfaces) and hdl_nd_flag_default_off (used for the M/O flags whose FRR default is disabled). This keeps the observable behaviour symmetric: creating then deleting a VLAN_INTERFACE entry leaves the interface in the same state as if the entry had never existed.

How to verify it

# Apply the config via apply-patch (full yang validation)
cat > /tmp/ra.json <<JSON
[
  {"op": "add", "path": "/VLAN_INTERFACE/Vlan100/nd_suppress_ra", "value": "false"},
  {"op": "add", "path": "/VLAN_INTERFACE/Vlan100/nd_managed_config_flag", "value": "true"},
  {"op": "add", "path": "/VLAN_INTERFACE/Vlan100/nd_ra_interval", "value": "30"}
]
JSON
sudo config apply-patch /tmp/ra.json

# Verify resulting FRR configuration
docker exec bgp vtysh -c 'show running-config' | grep -A6 '^interface Vlan100$'
# interface Vlan100
#  ipv6 nd managed-config-flag
#  ipv6 nd ra-interval 30
#  no ipv6 nd suppress-ra
# exit

Yang validation rejects invalid input:

# Invalid boolean
sudo config apply-patch '[{"op":"add","path":"/VLAN_INTERFACE/Vlan100/nd_suppress_ra","value":"garbage"}]'
# libyang: Invalid value "garbage" in "nd_suppress_ra" element.

# Out-of-range interval
sudo config apply-patch '[{"op":"add","path":"/VLAN_INTERFACE/Vlan100/nd_ra_interval","value":"99999"}]'
# Invalid IPv6 ND RA interval (expected range: 1..1800 seconds)

DELETE restores the FRR default:

sudo config apply-patch '[
  {"op":"remove","path":"/VLAN_INTERFACE/Vlan100/nd_suppress_ra"},
  {"op":"remove","path":"/VLAN_INTERFACE/Vlan100/nd_managed_config_flag"},
  {"op":"remove","path":"/VLAN_INTERFACE/Vlan100/nd_ra_interval"}
]'
docker exec bgp vtysh -c 'show running-config' | grep -A3 '^interface Vlan100$' || echo "(interface reverted to default)"

Tested on SONiC in unified routing config mode with FRR 10.4.1 on a
top-of-rack switch. Full test matrix (19 tests: 9 direct ConfigDB writes,
3 delete-semantics checks, 7 apply-patch end-to-end) passes.

Which release branch to backport (provide reason below if selected)

• 202205
• 202211
• 202305
• 202311
• 202405
• 202411
• 202505

Tested branch (Please provide the tested image version)

• master (based on commit 9a40754)

Description for the changelog

frr-mgmt-framework, YANG: add IPv6 ND/RA support for VLAN_INTERFACE

Link to config_db schema for YANG module changes

See HLD sonic-net/SONiC#2165 for the schema spec.

A picture of a cute animal (not mandatory but encouraged)

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• ✅ login: zedzean / name: Zaahir Ahmed Syed (05622c4)

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