This adds an IPv4 counterpart to `IPv6ProxyNDPAddress=` for adding
manual entries to the kernel's IPv4 neighbour proxy table (check via
`ip -4 neighbour show proxy dev <dev>`). systemd-networkd only exposed
`IPv4ProxyARP=` for per-interface `proxy_arp` sysctl (automatic proxy
ARP) with no way to manage manual entries from a .network file.
To avoid duplicating the IPv6 proxy NDP code path, both families are
now combined into a single new `networkd-neighbor-proxy` module. The
IPv6 behaviour is preserved: `IPv6ProxyNDPAddress=` still implies
`IPv6ProxyNDP=yes` unless `IPv6ProxyNDP=` is explicitly disabled and
entries are still dropped if the kernel has no IPv6 support.
The same rule is applied to `IPv4ProxyARPAddress=`. It implies
`IPv4ProxyARP=yes` when the sysctl is not explicitly set and has no
effect if `IPv4ProxyARP=` has been set to false.
This keeps the user model symmetric and predictable across both
families: a single per-address setting that turns on the matching
per-interface sysctl automatically, while still letting system
administrators opt out by setting the boolean explicitly to false.
Note that the IPv4 manual NTF_PROXY entries installed here would
actually function without `proxy_arp` (unlike IPv6, where `proxy_ndp`
gates the manual entries); the implication is kept for symmetry with
`IPv6ProxyNDPAddress=` and is now called out explicitly in the man
page, together with the fact that enabling `proxy_arp` also activates
interface-wide automatic proxy ARP for routed-toward addresses on
connected subnets.
Parser-time validation rejects addresses the kernel would refuse:
the ANY/null address for both families, IPv4 and IPv6 multicast
and the IPv4 limited broadcast 255.255.255.255.
Signed-off-by: Aritra Basu <aritrbas+gh@cisco.com>
We don't care about the ordering, so we may just as well drop the numerical
prefixes that we normally use for sorting. Also rename some other samples
to keep width of output down to reasonable width.
