I moved the DHCP Relay service down to the Layer2 switch, configured helpers and the ip default-gateway had to be in the same vlan as this vlan on the layer 2 switch (otherwise dhcp replies won't work). It was the only way in the end.
The configuration for the DHCP relay across the Site to Site tunnel was not correct and that's the reason why it was not working
In the crypto ACL you need to add the outside ip to the DHCP serevr as well
and the Vice versa on the remote end
So the correct Crypto acl would have been like this
access-list L2LVPN extended permit ip 10.1.13.0 255.255.255.0 10.1.99.0 255.255.255.0
access-list L2LVPN extended permit ip host 213.8.x.x 10.1.99.0 255.255.255.0
Since you already have the inside network in the crypto ACL so we are not adding the inside interface otherwise we would have to add that as well.
Basic understanding of the DHCP relay
1. Client starts the DHCP process by sending a DHCPDISCOVER message to destination address
255.255.255.255 - UDP port 67
2. ASA sees the broadcast and based on the dhcprelay server config it forwards the DHCPDISCOVER message as a unicast packet to the server's IP sourcing from the interface IP close to the server. In this case the outside IP address.
3. Server sends back DHCPOFFER as a unicast packet to the ASA - UDP port 67
Server will send it to the destination IP address of the inside interface (giaddr) which is the dhcprelay enabled interface.
4. This packet will arrive on the outside interface and will be broadcast out the inside interface - UDP port 68.
5. Client receives the DHCPOFFER, and sends a DHCPREQUEST message to the server, that it accepts the offer.
6. The server will send back a DHCPACK message to the client.
7. Client upon receiving the DHCPACK, it will start communicating on the network.
This is how the DHCP relay would work across the site to site tunnel.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...