The new syntax has explicit listen and upstream interface settings.

The ISC DHCP relay in VyOS is completely broken for my (non-GRE) use case, I would really like to see it get tossed out for something that works. This might not be the best place to describe my relay problems, but I might as well (skip this paragraph it you're not interested). My setup basically consists of the (ISC) DHCP server host connected to the VyOS router (running on a Dell R320), directly connected to a Cisco ASR920 router. Both VyOS and the ASR are directly connected to user VLANs (VyOS for firewalled/NATed zones and ASR for high-traffic users) and have DHCP relays set up targeting the DHCP server, such that the relayed messages from the ASR passes through the VyOS router towards the DHCP server and should get routed normally (i.e. ignored by the VyOS relay). The VyOS DHCP relay doesn't like this and starts spamming the DHCP messages up to ten or more times, causing wired clients to have to wait maybe ten seconds before getting an IPv4 address and wireless clients to just time out and abort the connection. I can provide the relay logs (mainly screenshots unless i dig up the disk I used) and VyOS config if anyone wants them, but as they have sensitive addresses, I don't intend to post them publicly. EDIT: I should mention that I didn't notice any problems while testing it with only myself, it was when 200 people started connecting the problems started occurring. And the DHCP server VM was not showing any noticable load.

If this package supports all existing setups and the GRE usecase I see no reason to not replace it. @basalblas PR is happily accepted.

Keep in mind you cannot run dhcp-helper and ISC DHCP server at the same time on a single router. The Vyos CLI should not allow this.

@dmbaturin @c-po
Not sure why did we merge these PRs. The isc-dhcp-relay does require at least two interfaces to work. This was discussed in details in T1276 and T2408.
As result the latest documentation is inaccurate what could make users confused.

I've created a PR in the vyos/vyos-1x repy for the config verification fix: https://github.com/vyos/vyos-1x/pull/208

I've created a PR in the vyos/vyos-documentation repo for the documentation fix: https://github.com/vyos/vyos-documentation/pull/190