[Bug 296652] ARP replies from bridge are lost (?runt packet)

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=296652

            Bug ID: 296652
           Summary: ARP replies from bridge are lost (?runt packet)
           Product: Base System
           Version: 15.1-STABLE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: [email protected]
          Reporter: [email protected]

Created attachment 272673
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=272673&action=edit
tar file of pcaps referred to in Additional Information

Overview:

ARP replies from a bridge are never received by the requesting router or by any
upstream network devices (i.e. managed switch) when using an intel i210 netowrk
card as the bridge's physical interface.
tcpdumps:
- on the host shows that the ARP request is received and the reply is sent
- on the upstream switch shows that the ARP request is received, but the reply
is never received.

ARP replies are received upstream when:
- a realtek network interface is used (instead of the intel interface), or 
- the IP address is attached to the intel interface (instead of to the bridge). 

Steps to reproduce:

- Attach intel i210 interface to the bridge,
- Apply IP address to the bridge (not igb0 interface)
- Force the upstream gateway to generate ARP requests (e.g. by deleting the
bridge's address from the gateway ARP table)

Actual results:

ARP replies are never received by any upstream network devices

Expected results:

ARP replies are received by upstream network devices

Build date and hardware:

FreeBSD 15.1
Intel i210

Additional information:

Tcpdump shows that the bridge is generating a 46 byte ethernet frame and that
igb0 is passing the 46 byte frame. This frame is never received by the upstream
switch. (See test1 pcaps)

When I remove igb0 and replace it with re0, the tcpdump shows that bridge0 is
still producing 46 byte frames, but re0 is adding padding to create a 64 byte
frame that is received by the upstream switch. (See test2 pcaps)

When I attach the IP address to the igb0 interface instead of the bridge, igb0
still produces a 46 byte frame, but it is received upstream as a 64 byte frame.
The bridge never sees the ARP reply. (See test3 pcaps)

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