sonic-yang: model BGP afi_safi as an enumeration instead of an unconstrained string

[bhouse-nexthop]

Why I did it

The afi_safi list keys across the BGP models were declared type string with no enumeration, so any value was valid YANG. Both ipv4-unicast (hyphen) and ipv4_unicast (underscore) validated and committed, producing two distinct AF rows — only the underscore spelling is functional, since CONFIG_DB, bgpcfgd and frrcfgd all use underscores.

This is a model gap, not a CLI defect. nhcli derives all config-mode validation and completion from the YANG, so an unconstrained key is faithfully accepted; the fix belongs in the model. It also explains the original report (Randy Williams) that tab-completion walks you to the afi-safi position and then leaves you to type the value blind — there were no enum values for the CLI to offer.

Two further BGP leaves had the same shape of problem — declared type string while their consumers accept only a specific form — and are fixed here too: BGP_GLOBALS.rr_cluster_id and the BGP_DEVICE_GLOBAL confederation peers list.

How I did it

Added a bgp_afi_safi typedef to sonic-bgp-common.yang with the canonical underscore values, plus two restrictions for the contexts whose vocabulary is narrower, and wired all five afi_safi leaves to them:

Table	Type	Values
BGP_NEIGHBOR_AF / BGP_PEER_GROUP_AF	bgp_afi_safi	ipv4_unicast, ipv6_unicast, l2vpn_evpn, ipv4_srpolicy, ipv6_srpolicy
BGP_GLOBALS_AF	bgp_afi_safi_global	as above, minus SR-Policy
BGP_GLOBALS_AF_AGGREGATE_ADDR	bgp_afi_safi_global	"
BGP_GLOBALS_AF_NETWORK	bgp_afi_safi_global	"
BGP_DEVICE_GLOBAL_AF	bgp_afi_safi_device_global	ipv4_unicast, ipv6_unicast

The per-context sets are derived from the actual consumers, not from prose. SR-Policy is excluded from the globals tables because frrcfgd installs no global SR-Policy config (frrcfgd.py:3618). BGP_DEVICE_GLOBAL_AF is unicast-only because AFI_SAFI_MAP in bgpcfgd/managers_device_global_af.py:9 has exactly two entries and log_warns away anything else. This follows how these files already model sibling leaves (bgp_peer_type, bgp_community_type, bgp_tx_add_paths_type are all enumerations).

Constraining the key type makes several hand-written guards unreachable, so they are removed:

• the three must "not(contains(., 'srpolicy'))" clauses on the BGP_GLOBALS_AF lists
• the install_backup_path unicast must on BGP_DEVICE_GLOBAL_AF, whose key type now admits only the two unicast families

The equivalent install_backup_path guard on BGP_GLOBALS_AF is kept — l2vpn_evpn is still a valid key there, so that constraint is still live.

*_multicast is deliberately excluded: no consumer implements it. The BGP_DEVICE_GLOBAL_AF_LIST description previously advertised ipv4_multicast / ipv6_multicast / l2vpn_evpn, none of which AFI_SAFI_MAP supports; that description is corrected.

No CLI code changes. libyang validates a list key against its declared type, so an out-of-enum afi_safi is rejected at commit across every entry point, and the enum values become completion candidates.

Additionally constrained (same class of gap, not afi_safi):

• sonic-bgp-global.yang rr_cluster_id — renders into bgp cluster-id, which takes an IPv4 address or a 32-bit integer. Now a union of inet:ipv4-address and uint32 { range "1..4294967295"; }.
• sonic-bgp-device-global.yang CONFED peers — documented as semi-colon-separated sub-ASNs, previously unvalidated. Now pattern "[1-9][0-9]*(;[1-9][0-9]*)*". The pattern enforces the shape only; it does not range-check each sub-ASN against the 32-bit AS maximum, which would need a leaf-list.

The existing "66000;63000" sample in the tests and in doc/Configuration.md satisfies the new pattern. No existing rr_cluster_id values exist anywhere in the repo.

How to verify it

Build and see yang model tests succeed.

Which release branch to port

• 202605
• 202511
• 202505

Tested branch (Please provide the tested image version)

• master as of 20260723

Description for the changelog

sonic-yang: constrain BGP afi_safi list keys, rr_cluster_id and confederation peers instead of leaving them unconstrained strings

Link to config_db schema for YANG module changes

https://github.com/sonic-net/sonic-buildimage/blob/master/src/sonic-yang-models/doc/Configuration.md#bgp_globals_af

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