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Apologies for my newbie question. I have recently had a Mellanox switch added to the mix. I was using an "IP helper-address" to forward DHCP requests in different VLANs to my DHCP server(s) on my other switches. I see you can configure a DHCP relay agent on the Mellanox switch but it was my understanding that this works differently from the IP helper-address. i.e in the DHCP relay the router receives the request and builds a new request to send to the server. I see there is a vrf-auto-helper but I can't quite get my head around what this is supposed to do.

On a Cisco-esque switch I have:

interface VLAN ??
 ip address a.b.c.254 255.255.255.0
 ip helper-address {address of dhcp server}

How would I achieve the same result on a Mellanox switch?

Would this be an equivalent?

# DHCP relay configuration
##
   ip dhcp relay instance 1 vrf default
   ip dhcp relay instance 1 vrf-auto-helper
   ip dhcp relay instance 1 address {address of dhcp server}
   ip dhcp relay instance 1 always-on
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1 Answer 1

5

Here is a configuration example on Mellanox Onyx:

##
## DHCP relay configuration
##
   ip dhcp relay instance 1 vrf default
   ip dhcp relay instance 1 address 10.100.100.1
   ip dhcp relay instance 1 always-on
   interface vlan 1 ip dhcp relay instance 1 downstream
   interface vlan 30 ip dhcp relay instance 1 downstream
   interface vlan 197 ip dhcp relay instance 1 downstream

As you can see the configuration is not done under the vlan interface, but rather the VLAN(s) are added in the dhcp instance relay configuration.

Edit after question update:

Yes using:

 ip dhcp relay instance 1 vrf-auto-helper

should enable the configured dhcp relay for all L3 interfaces within the specified VRF

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  • Thanks for that. Sorry, I overlapped slightly in modiftying my question to include what I was thinking for a config. I'll give what you suggested a go
    – user993269
    Feb 23 at 13:15
  • @user993269 I have edited the answer.
    – JFL
    Feb 23 at 15:59
  • Thanks so much for your help
    – user993269
    Feb 23 at 16:30

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