View source for DHCP RELAY over L2TPv3

== Introduction ==
A DHCP relay agent allows the DHCP clients to obtain IP addresses from a DHCP server that is not configured on the same LAN. 

This article provides a configuration example with details on how to set-up a DHCP relay over a L2TPv3 VPN. 

== Prerequisites ==
You will need:

* Two RUT or RUTX devices (one as Server and other as Client)
* A PC acting as a Host for testing
* Both routers must have a Public Static or Public Dynamic IP addresses

== Configuration Scheme ==
I will paste a Topology Image here

== DHCP Server Settings ==

=== DHCP Pool ===
Enter the router's WebUI, go to '''Network > Interfaces > Ethernet LAN''' and click the '''<nowiki/>'Edit'''' button on the right side of the interface to set the LAN network address.

[[File:Server new 01 fixed.png|border|class=tlt-border|750x750px]]

Under '''DHCP SERVER''' set parameters for the DHCP pool.
[[File:Server new 02.png|alt=|center|464x464px|border|class=tlt-border]]

===Set up Mobile WAN as Main WAN ===
Enter to the router’s WebUI, go to '''Network > Interfaces''' press mouse click on the Mobile Wan interface, then drag it to the 1<sup>st</sup> position and then press '''Save & Apply'''.
[[File:Server new 03.png|alt=Mobile WAN as Main WAN|center|thumb|504x504px|Mobile WAN as Main WAN]]

===Create L2TPv3 instance ===
Go to router’s WebUI, under '''Service > VPN > L2TP > L2TPv3''' and create new '''L2TPV3''' instance.

'''LOCAL SETTING'''

Local address: 84.15.155.201

Tunnel ID: 100

Session ID: 100

Cookie: 12ABCDEF

'''PEER SETTING'''

Peer address: 84.15.249.182

Peer Tunnel ID: 10

Peer Session ID: 10

Peer Cookie: 12ABCDEF

'''INSTANCE SETTING'''

Bridge to: LAN

MTU: 1500

Encapsulation: IP

Layer 2 specific header type: Linux Default

[[File:Server new 04 01.png|alt=L2TPv3 Server settings|center|thumb|488x488px|L2TPv3 Server settings]]
[[File:Server new 04 02.png|alt=L2TPv3 Server Settings|center|thumb|480x480px|L2TPv3 Server Settings]]Specify the Local address of your mobile WAN. Local value for Tunnel ID, session ID and Cookie must match with the peer values being used at the other end.

==DHCP Client Settings (Relay)==

===DHCP Relay ===
Enter the router's WebUI, go to '''Network > Interface > LAN > DHCP Server''' and change the "'''Enable DHCP'''" field value from Enable to Relay and type in the DHCP Server the IP address of the server. Click Save & Apply.
[[File:Client 01.png|alt=Enable DHCP Relay|center|thumb|517x517px|Enable DHCP Relay]]
'''Note:''' The IPv4 address of the LAN interface is different from the server's LAN interface address, this is necessary to avoid conflicts.

===Set up Mobile WAN as Main WAN ===
Enter to the router’s WebUI, go to '''Network > Interfaces''' press mouse click on the Mobile Wan interface, then drag it to the 1<sup>st</sup> position and then press '''Save & Apply'''.
[[File:Client 02.png|alt=Mobile WAN as Main WAN|center|thumb|545x545px|Mobile WAN as Main WAN]]

===Modify Enable-DHCP-renew firewall rule ===
Enter in the router’s WebUI, go to '''Network > Firewall > Traffic rules''' to additionally allow destination port 67.
[[File:Client 03.png|alt=DHCP renew firewall rule|center|thumb|555x555px|DHCP renew firewall rule]]

===Create L2TPv3 instance ===
Go to router’s WebUI, under '''Service > VPN > L2TP > L2TPv3''' and create new '''L2TPV3''' instance.

'''LOCAL SETTING'''

Local address: 84.15.249.182

Tunnel ID: 10

Session ID: 10

Cookie: 12ABCDEF

'''PEER SETTING'''

Peer address: 84.15.155.201

Peer Tunnel ID: 100

Peer Session ID: 100

Peer Cookie: 12ABCDEF

'''INSTANCE SETTING'''

Bridge to: LAN

MTU: 1500

Encapsulation: IP

Layer 2 specific header type: Linux Default
[[File:Client 04.png|alt=L2TPv3 Client instance|center|thumb|517x517px|L2TPv3 Client Settings]]
[[File:Server new 04 02.png|alt=L2TPv3 Client Settings|center|thumb|523x523px|L2TPv3 Client Settings]]


==Testing DHCP over L2TPv3==
To test the realy settings go to DHCP server to check that devices are able to recieve IP addresses in the range 192.168.10.150 - 192.168.10.170 either via LAN port or Wi-Fi. Access the CLI  and run '''cat /tmp/dhcp.leases''' to list all DHCP clients.
[[File:Test 01.png|alt=DHCP clients|center|thumb|508x508px|DHCP clients]]
Asking for the Address Resolution Protocol (ARP) table is also an other method to find hosts on the LAN network.
[[File:Test 02.png|alt=DHCP Clients|center|thumb|513x513px|DHCP Clients]]