missing SYN/ACK for inbound TCP solved by altering broadcast address - why?

I've found a workaround for this issue, but don't understand why this
occurs. Reading RFC1122 has left me none the wiser. What am I missing?
Is this a Linuxism or simple a standardisation loophole?

## Problem

- on 13.1-R, dhclient-set config works for all UDP, & outbound TCP
- but inbound TCP connections send no SYN/ACK at all back
- on Linux Ubuntu 22.04 & others, the DHCP supplied IP config
  works as expected

failing FreeBSD config from dhclient:
  inet 147.75.93.61 netmask 0xfffffffe broadcast 147.75.93.60
                                                 ^^^^^^^^^^^^

working Linux config (note broadcast)
  inet 147.75.93.61 netmask 0xfffffffe broadcast 255.255.255.254
                                                 ^^^^^^^^^^^^^^^

- full details below (dhcp lease, ifconfigs etc)

I worked around this by forcing broadcast-address in dhclient.conf:

## /etc/dhclient.conf
interface "ice0" {
  supersede broadcast-address 255.255.255.255;
}
# repeat for other ifaces as required

Which is ~ok~ for the moment, but I'd like to understand why this
occurs, and fix it properly. Either at DHCPD end, or FreeBSD
config.



# Further details

- Ubuntu 22.04 from vendor
- FreeBSD 13.1-RELEASE amd64 vanilla install
- 4x ice(4) NICs (Intel E810) and 2x (unused) ix (igxbe)
- 2x of the ice(4) are bonded link aggregation
- dhclient only used to attach to 1 nic, ignoring FreeBSD side of bonding


## Linux ip addr

# ip addr
8: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether b4:96:91:d9:99:20 brd ff:ff:ff:ff:ff:ff
    inet 147.75.92.187/31 brd 255.255.255.255 scope global bond0
...

## FreeBSD ifconfig

# ifconfig ice0
ice0: flags=8863<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=4e10438<VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,LRO,VLAN_HWFILTER,RXCSUM_IPV6,TXCSUM_IPV6,NOMAP>
        ether b4:96:91:d9:9b:48
        inet 147.75.93.61 netmask 0xfffffffe broadcast 147.75.93.60
        media: Ethernet autoselect (25G-AUI <full-duplex>)
        status: active
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
...
root@metalBSD:~ # netstat -4rn
Routing tables

Internet:
Destination        Gateway            Flags     Netif Expire
default            147.75.93.60       UGS        ice0
127.0.0.1          link#7             UH          lo0
147.75.93.60/31    link#3             U          ice0
147.75.93.61       link#3             UHS         lo0

root@metalBSD:~ # cat /var/db/dhclient.leases.ice0

- note no broadcast-address provided
- Linux & FreeBSD evidently derive it differently

lease {
  interface "ice0";
  fixed-address 147.75.93.61;
  option subnet-mask 255.255.255.254;
  option routers 147.75.93.60;
  option domain-name-servers 147.75.207.207,147.75.207.208;
  option host-name "intransigent09";
  option dhcp-lease-time 172800;
  option dhcp-message-type 5;
  option dhcp-server-identifier 139.178.78.140;
  renew 1 2022/6/27 18:40:06;
  rebind 2 2022/6/28 12:40:06;
  expire 2 2022/6/28 18:40:06;
}

A+
Dave