SG300-20 - error with dhcp snooping / dhcp relay

[brsysadmin]

Hello,

I have three SG300-20 on my network :

Switch1 - ports 1, 2, 3 are linkes with Switch 2 - ports 1, 2, 3 (LACP - LAG1)

Switch 1 - ports 4, 5, 6 are linkes witch Switch 3 - ports 1, 2, 3 (LACP - LAG2)

I have three vlan :

  - 10 : for my company

  - 20 : for my guest

  - 30 : for my partner

My DHCP Server (Linux) is link on Switch 1 - port 7.

I enabled the DHCP snooping and dhcp relay but no activated the option 82 :

  - switch 1 - port 7 : trusted

  - switch 2 - LAG 1 : trusted

  - switch 3 - LAG 2 - trusted

I specified the IP address of my DHCP server to relay on the three switches.

My clients receive IP addresses but I get errors on the switch 1 :

%DHCPSNOOP-E-HDRMAC: DHCP packet mac addresses verification problem - packet dropped: vlan - 20, port - Po2, mac source address - <mac_address_switch3>, mac dest ad dress - <mac_adress_dhcp_server>, hw client address - <mac_adress_client_connect_on_switch3>, error - DHCPSnP_packet_callback

Someone would have an idea of ​​where the problem is?

I thank you in advance.

B.R

[brsysadmin]

Is the DHCP relay must be enabled on all switches in cascade or only one on which is connected to the dhcp server?

I thank you in advance.

B.R

[Aleksandra Dargiel]

Hi B.R,

DHCP relay needs to be configure on the broadcast boundaries. Broadcast domain should be extended to the routing device on your network where you would normally configure DHCP relay.

Kind regards,

Aleksandra

[brsysadmin]

Thank you for your response but I'm not sure I understood what you meant.

In the case of several cascaded switches (in "line"), do I need to configure the relay on the switch connected to the DHCP server or on all the switches of the line?

[Aleksandra Dargiel]

Hi BR,

which switch is doing routing on this network?

Aleksandra

[brsysadmin]

Hello, There are no routes between my VLAN's. But the switch 1 goes to a Linux server that could possibly router. This server is a DHCP server. The DHCP error that relates to VLAN 20. The PC that runs the DHCP request is allowed only on VLAN 10.

[Aleksandra Dargiel]

Hi,

Is your DHCP server in VLAN 10? and PC on VLAN 20 cannot get IP? if this is the case you need to set up layer 3 device whcih would have IP interface in both VLANs and relay bootp from VLAN 20 to VLAN 10.

Regards,

Aleksandra

[brsysadmin]

Hi, All switches are configured as Level 3 and has an IP in all VLAN's. My DHCP server also has an IP in all VLAN's. So VLAN 10 receives IP addresses from the network 192.168.10.0/24 and VLAN 20 receives IP addresses from the network 192.168.20.0/24. For cons, the error I mentioned at the top corresponds to a PC VLAN 10 who is receiving an IP address 192.168.10.0/24 but I do not know why the error speaks VLAN 20.