[Bug 247912] IPv6 ndp does not work across local bridge members

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=247912

            Bug ID: 247912
           Summary: IPv6 ndp does not work across local bridge members
           Product: Base System
           Version: 12.1-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: bugs at FreeBSD.org
          Reporter: d8zNeCFG at aon.at

Scenario:
- FreeBSD 12.1 release patch level 6 acting as bhyve host
- The host has a local Ethernet interface em0 with IPv4 and IPv6 addresses
assigned; all these addresses are announced via DNS and /etc/hosts
- Via em0, the host sees several other machines on the network; all have IPv4
and IPv6 addresses assigned, as well as DNS and /etc/hosts entries
- Using bhyve to run guests (FreeBSD 12.1 amd64 and i386, and head amd64)
- In order to use bhyve, create bridge and tap interfaces as follows:

# sysctl net.link.tap.up_on_open=1
# ifconfig bridge0 create && ifconfig bridge0 addm em0 && ifconfig bridge0 up
# ifconfig tap905 create && ifconfig bridge0 addm tap905
# sh /usr/share/examples/bhyve/vmrun.sh -u -c 4 -m 3G -t tap905 -d <disk
device> <vm name>

Result:
- When using "ndp -a" in the bhyve client, entries for all remote machines
exist correctly.
- However, there is no entry for the IPv6 address associated with the
bridged-to interface em0
- As a result, it is not possible to reach services on the host system from the
bhyve client via IPv6 (IPv4 is working)

Scenario (continued):
- Manually add ndp entries in the client:

# ndp -s <IPv6 address of host's em0> <Ethernet address of host's em0>

Result:
- It is now possible to reach services on the host system from the client
system via IPv6

Expected result:
- NDP should be working also for the host's interface em0 which is bridged to
bridge0, and not only for interfaces of remote machines

Note:
- The exactly same issue is seen on another bhyve host with re0 as physical
interface

-- Martin

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