Although it is possible to specify "network" and "broadcast" configuration lines, they are not only unnecessary, they can be a source of configuration error that is hard to spot. You should allow the system to compute both these values from the "netmask" and "address" configuration.
Using NIC dev eth0, vlan "cscfnet" for this example, you should end up with a file in "/etc/network/interfaces.d" or a section in the /etc/network/interfaces file that contains the lines:
The following CS Internet Vlans also have an IPv6 address range assigned to them.
| Vlan Name | IPv4 subnet | IPv6 subnet |
|---|---|---|
| cscfnet | 129.97.15.0/24 | 2620:101:f000:4805::64 |
| cs-teaching-net | 129.97.167.0/26 | 2620:101:f000:4804::64 |
| cs-general-net | 129.97.167.64/26 | 2620:101:f000:4803::64 |
which means we want to assign the IPv6 address as well.
Using NIC dev eno1, vlan "cs-general-net" for this example, you should end up with a file in "/etc/network/interfaced.d" or a section in the /etc/network/interfaces file that contains the lines: