Ethernet Switches & Routers

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New Contributor
Posts: 2
Registered: ‎01-27-2012

DHCP and Link Aggregation BI-RX-16

Hi All,

I have an issue where I am not getting DHCP responses even though my DHCP server is sending them.

Setup:

BI-RX-16 has dual connections (LAG) to a server which we want to install over the network via DHCP, BOOTP and then TFTP. Obviously at BIOS time the link is not aggregated. The DHCP request is sent out of Eth0 and received by the DHCP server (different subnet off different Cisco switch via ip-helper) which responds with an IP Address. The response is never received at the server DHCP'ing.

If I remove the second ethernet cable it all works perfectly so I figure it must be a LAG problem.

I am wondering whether due to link aggregration the DHCP response is being sent down the other ethernet port due to some load balancing.

Please help as removing the cable to allow this install to occur seems wrong as I have never had this trouble on a Cisco or Dell switch.

Contributor
Posts: 61
Registered: ‎12-08-2009

Re: DHCP and Link Aggregation BI-RX-16

it seems your dhcp requests does not pass through RX when you have a LAG between server and the RX chassis but do you have connectivity when you use LAG?
it is better to troubleshoot basic connectivity over LAG before you go into DHCP related troubleshooting.
you may need to change your LAG configuration on RX and on the server side.

New Contributor
Posts: 2
Registered: ‎01-27-2012

Re: DHCP and Link Aggregation BI-RX-16

Thanks for the reply.

Once installed the NIC bonding works perfectly between the server and the switch (with and without the second cable plugged in)

It seems only to be a problem during DHCP when the NICs are not bonded on the server. I assume for this reason the switch is alternating which link it sends the packets down to the server resulting in the loss of every second packet.

Contributor
Posts: 61
Registered: ‎12-08-2009

Re: DHCP and Link Aggregation BI-RX-16

if your LAG and NIC configuration works ok maybe you need to tell your DHCP service that it will receive packets through all bonded NIC interfaces. your dhcp may be waiting requests from one interface.I guess  you should focus on the server/dhcp configuration if you are sure about your LAG definitions.

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