daisychain rows to detect value

I have a table of network ports. These ports are part of something, be it a
cabinet patch panel, or a network switch.

np_connects_to references a hardware ID, which can be the cabinet,
switch,router etc. containing the port.
no_port is the name of the port.
np_untagged_vlan is the VLAN ID for the port, with NULL being allowed.

Each port can then be patched to another port.

For example:

np_connects_to | np_port | np_patch_to | np_patch_port | np_untagged_vlan
---------------+---------+-------------+---------------+-----------------
1 | 01 | | | 1
2 | 23B | 1 | 01 |
3 | 23A | 2 | 23B |

Row 1 shows a switch port set to VLAN 1.
Row 2 shows a port in cabiner 'A' (Panel B port 23) which is patched to the
switch port.
Row 3 shows a port in cabinet 'B' (Panel A port 23) which is the other end
cabinet A port 23B

Is there a way to be able to propogate the untagged VLAN to any port patched
to it?

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