[Edgecore SONiC] DHCP Relay Follow
When the DHCP Relay service is enabled, and the switch sees a DHCP client request from an attached host, it inserts its own IP address into the request so that the DHCP server will know the subnet where the client is located. Then, the switch forwards the packet to a DHCP server (destination IP) on another network. When the server receives the DHCP request, it allocates a free IP address for the DHCP client from its defined scope for the DHCP client’s subnet, and sends a DHCP response back to the DHCP Relay agent (the switch). The switch then passes the DHCP response received from the server to the client.
Restriction:
- DHCP relay support VLAN interface only.
- DHCP relay won’t work well when the VLAN is belong to Non-default VRF.
- In 202012 branch, DHCP relay only work well when the DEVICE_METADATA.type is ToRRouter. (Default configuration is LeafRouter.)
admin@sonic:~$ show runningconfiguration all | jq .DEVICE_METADATA
{
"localhost": {
"bgp_asn": "65100",
"buffer_model": "traditional",
"default_bgp_status": "up",
"default_pfcwd_status": "disable",
"hostname": "sonic",
"hwsku": "Accton-AS5835-54X",
"mac": "04:f8:f8:8d:81:e1",
"platform": "x86_64-accton_as5835_54x-r0",
"type": "ToRRouter"
}
}
DHCP relay between VLANs
Tested model & firmware version:
- Switch model name:
AS7726-32X
AS4630-54PE
- Edgecore SONiC version:
202006.3
202006.4
202012.1
202012.2
Topology:
Pre-configuration:
- Ethernet4 breakout to 4x10G.(refer Dynamic Port Breakout)
admin@sonic:~$ show interface status Ethernet4-7
Interface Lanes Speed MTU FEC Alias Vlan Oper Admin Type Asym PFC Oper Speed
----------- ------- ------- ----- ----- ------------- ------ ------ ------- -------------- ---------- ------------
Ethernet4 5 10G 9100 none Eth2/1(Port2) trunk up up QSFP+ or later N/A 10G
Ethernet5 6 10G 9100 none Eth2/2(Port2) trunk up up QSFP+ or later N/A 10G
Ethernet6 7 10G 9100 none Eth2/3(Port2) routed up up QSFP+ or later N/A 10G
Ethernet7 8 10G 9100 none Eth2/4(Port2) routed down up QSFP+ or later N/A 10G
- VLAN configuration is as topology.(refer to VLAN & Inter-VLAN Routing)
admin@sonic:~$ show vlan brief
+-----------+--------------+-----------+----------------+---------------+---------------+-------------+-------------+
| VLAN ID | IP Address | Ports | Port Tagging | DHCP Helper | DHCP Source | DHCP Link | Proxy ARP |
| | | | | Address | Interface | Selection | |
+===========+==============+===========+================+===============+===============+=============+=============+
| 10 | | Ethernet4 | untagged | | | | disabled |
+-----------+--------------+-----------+----------------+---------------+---------------+-------------+-------------+
| 20 | | Ethernet5 | untagged | | | | disabled |
+-----------+--------------+-----------+----------------+---------------+---------------+-------------+-------------+
- IP binding is as topology.(refer to Management and front port IPv4/IPv6 Address)
admin@sonic:~$ show ip interfaces
Interface Master IPv4 address/mask Admin/Oper BGP Neighbor Neighbor IP
----------- -------- ------------------- ------------ -------------- -------------
Loopback0 10.1.0.1/32 up/up N/A N/A
Vlan10 192.168.10.1/24 up/up N/A N/A
Vlan20 192.168.20.1/24 up/up N/A N/A
docker0 240.127.1.1/24 up/down N/A N/A
eth0 192.168.254.1/24 up/up N/A N/A
lo 127.0.0.1/16 up/up N/A N/A
Expect result:
DHCP client can get IP via DHCP relay from remote DHCP server.
Procedure:
Steps 1. Create a JSON file for modify DEVICE_METADATA.type.
admin@sonic:~$ cat tor.json
{
"DEVICE_METADATA": {
"localhost": {
"type": "ToRRouter"
}
}
}
Steps 2. Apply the tor.json to running configuration.
admin@sonic:~$ sudo config load tor.json -y
Running command: /usr/local/bin/sonic-cfggen -j tor.json --write-to-db
Steps 3. Save to startup configuration and reboot device to apply.
admin@sonic:~$ sudo config save -y
Running command: /usr/local/bin/sonic-cfggen -d --print-data > /etc/sonic/config_db.json
admin@sonic:~$ sudo reboot
Steps 4. Enable DHCP relay on Vlan10.
admin@sonic:~$ sudo config vlan dhcp_relay add 10 192.168.20.100
Added DHCP relay destination address 192.168.20.100 to Vlan10
Restarting DHCP relay service...
Steps 5. Check switch can reach to DHCP server and the arp table has been correctly learned.
admin@sonic:~$ show vlan brief
+-----------+-----------------+-----------+----------------+----------------+---------------+-------------+-------------+
| VLAN ID | IP Address | Ports | Port Tagging | DHCP Helper | DHCP Source | DHCP Link | Proxy ARP |
| | | | | Address | Interface | Selection | |
+===========+=================+===========+================+================+===============+=============+=============+
| 10 | 192.168.10.1/24 | Ethernet4 | untagged | 192.168.20.100 | | | disabled |
+-----------+-----------------+-----------+----------------+----------------+---------------+-------------+-------------+
| 20 | 192.168.20.1/24 | Ethernet5 | untagged | | | | disabled |
+-----------+-----------------+-----------+----------------+----------------+---------------+-------------+-------------+
admin@sonic:~$ show arp
Address MacAddress Iface Vlan
--------------- ----------------- --------- ------
192.168.20.100 8c:ea:1b:30:da:51 Ethernet5 20
Total number of entries 1
The source interface of DHCP relay agent uses the LOOPBACK interface.
Tested model & firmware version:
- Switch model name:
AS7726-32X
- Edgecore SONiC version:
202012.2
Topology:
Pre-configuration:
- 202012 branch
- Ethernet4 breakout to 4x10G.(refer Dynamic Port Breakout)
admin@sonic:~$ show interface status Ethernet4-7
Interface Lanes Speed MTU FEC Alias Vlan Oper Admin Type Asym PFC Oper Speed
----------- ------- ------- ----- ----- ------------- ------ ------ ------- -------------- ---------- ------------
Ethernet4 5 10G 9100 none Eth2/1(Port2) trunk up up QSFP+ or later N/A 10G
Ethernet5 6 10G 9100 none Eth2/2(Port2) trunk up up QSFP+ or later N/A 10G
Ethernet6 7 10G 9100 none Eth2/3(Port2) routed up up QSFP+ or later N/A 10G
Ethernet7 8 10G 9100 none Eth2/4(Port2) routed down up QSFP+ or later N/A 10G
- VLAN configuration is as topology.(refer to VLAN & Inter-VLAN Routing)
admin@sonic:~$ show vlan brief
+-----------+--------------+-----------+----------------+---------------+---------------+-------------+-------------+
| VLAN ID | IP Address | Ports | Port Tagging | DHCP Helper | DHCP Source | DHCP Link | Proxy ARP |
| | | | | Address | Interface | Selection | |
+===========+==============+===========+================+===============+===============+=============+=============+
| 10 | | Ethernet4 | untagged | | | | disabled |
+-----------+--------------+-----------+----------------+---------------+---------------+-------------+-------------+
| 20 | | Ethernet5 | untagged | | | | disabled |
+-----------+--------------+-----------+----------------+---------------+---------------+-------------+-------------+
- IP binding is as topology.(refer to Management and front port IPv4/IPv6 Address)
admin@sonic:~$ show ip interfaces
Interface Master IPv4 address/mask Admin/Oper BGP Neighbor Neighbor IP
----------- -------- ------------------- ------------ -------------- -------------
Loopback0 1.1.1.1/32 up/up N/A N/A
Vlan10 192.168.10.1/24 up/up N/A N/A
Vlan20 192.168.20.1/24 up/up N/A N/A
docker0 240.127.1.1/24 up/down N/A N/A
eth0 192.168.254.1/24 up/up N/A N/A
lo 127.0.0.1/16 up/up N/A N/A
Expect result:
DHCP client will get IP from DHCP server. DHCP server will get DHCP request from DHCP client which source IP is Loopback interface IP.
Procedure:
Steps 1. Modify the type of DEVICE_METADATA to "ToRRouter" in /etc/sonic/config_db.json.
admin@sonic:~$ sudo sed -i 's/LeafRouter/ToRRouter/g' /etc/sonic/config_db.json
Steps 2. Reboot device to apply the configuration.
admin@sonic:~$ sudo reboot
Steps 3. Enable DHCP relay on VLAN10
admin@sonic:~$ sudo config vlan dhcp_relay add 10 192.168.20.100
Added DHCP relay destination address 192.168.20.100 to Vlan10
Restarting DHCP relay service...
Steps 4. Modify the src_intf to change the source IP of DHCP relay agent.
admin@sonic:~$ sudo config vlan dhcp_relay src_intf add 10 Loopback0
Added DHCP relay source interface Loopback0 for Vlan10
Restarting DHCP relay service...
Steps 5. Check switch can reach to DHCP server and the arp table has been correctly learned.
admin@sonic:~$ show vlan brief
+-----------+-----------------+-----------+----------------+----------------+---------------+-------------+-------------+
| VLAN ID | IP Address | Ports | Port Tagging | DHCP Helper | DHCP Source | DHCP Link | Proxy ARP |
| | | | | Address | Interface | Selection | |
+===========+=================+===========+================+================+===============+=============+=============+
| 10 | 192.168.10.1/24 | Ethernet4 | untagged | 192.168.20.100 | Loopback0 | | disabled |
+-----------+-----------------+-----------+----------------+----------------+---------------+-------------+-------------+
| 20 | 192.168.20.1/24 | Ethernet5 | untagged | | | | disabled |
+-----------+-----------------+-----------+----------------+----------------+---------------+-------------+-------------+
admin@sonic:~$ show arp
Address MacAddress Iface Vlan
--------------- ----------------- --------- ------
192.168.20.100 8c:ea:1b:30:da:51 Ethernet5 20
Total number of entries 1
Result:
As expect result.
- Packet capture
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