DHCP Relay

Example: DHCP Relay

Restriction:

1. There is no SONiC command for DHCP Relay

Reference model:

• Switch model name: AS7816-64X
• Edgecore SONiC version: SONiC.Edgecore-SONiC_20200116_051623_ec201904_128

Topology :

DHCP server belongs to VLAN 10 and connects to the switch Ethernet4.

DHCP client belongs to VLAN 20 and connects to the switch Ethernet2.

Procedure :

Step 1. Configure VLAN and IP address properly (Refer to this article)

Create VLAN10 with member Ethernet4 and binding the IP to VLAN10. 

admin@sonic:~$ sudo config vlan add 10    
admin@sonic:~$ sudo config vlan member add -u 10 Ethernet4     
admin@sonic:~$ sudo config interface ip add Vlan10 192.168.10.10/24

Create VLAN20 with member Ethernet2 and binding the IP to VLAN20. 

admin@sonic:~$ sudo config vlan add 20    
admin@sonic:~$ sudo config vlan member add -u 20 Ethernet2    
admin@sonic:~$ sudo config interface ip add Vlan20 192.168.20.10/24

Step 2. Save above setting to config_db.json

admin@sonic:~$ sudo config save -y

Step 3. Edit the file /etc/sonic/config_db.json

Add DHCP relay server IP address to VLAN 20 which DHCP client belongs to

admin@sonic:/etc/sonic$ sudo vi config_db.json   
{
    omitted...
    "VLAN": {
        "Vlan10": {
            "members": [
                "Ethernet4"
            ],
            "vlanid": "10"
        },
        "Vlan20": {
            "dhcp_servers": [
                "192.168.1.10"
            ],
            "members": [
                "Ethernet2"
            ],
            "vlanid": "20"
        }
    },
    "VLAN_INTERFACE": {
        "Vlan10|192.168.10.10/24": {},
        "Vlan20|192.168.20.10/24": {}
    },
    "VLAN_MEMBER": {
        "Vlan10|Ethernet4": {
            "tagging_mode": "untagged"
        },
        "Vlan20|Ethernet2": {
            "tagging_mode": "untagged"
        }
    },
    omitted...
}

Step 4.config reload or power cycle the switch

admin@sonic:~$ sudo config reload -y

Step 5. Check the setting information by SONiC command.

admin@sonic:~$ show vlan brief         
+-----------+------------------+-----------+----------------+-----------------------+
|   VLAN ID | IP Address       | Ports     | Port Tagging   | DHCP Helper Address   |
+===========+==================+===========+================+=======================+
|        10 | 192.168.10.10/24 | Ethernet4 | untagged       |                       |
+-----------+------------------+-----------+----------------+-----------------------+
|        20 | 192.168.20.10/24 | Ethernet2 | untagged       | 192.168.10.2          |
+-----------+------------------+-----------+----------------+-----------------------+

Result: VLAN20 DHCP client could obtain IP address from VLAN20 DHCP Server through the switch.