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Occasional Contributor
Posts: 12
Registered: ‎2012-07-20

GS752TXS DHCP Helper address

I am trying to configure my stack of GS752TXS to use one DHCP server across 3 VLANs. I don't see an option to add a DHCP helper address. I read on a review a user was also unable to find this but used a workaround by trunking the port with the DHCP server. I tried this but my DHCP server still did not provide addresses to items outside of the PVID. I then contacted Netgear support and they said I needed to trunk it to a PVID not on a VLAN like 99. This did not work either. Anyone know how to work around this?
Initial Contributor
Posts: 3
Registered: ‎2012-04-23

Re: GS752TXS DHCP Helper address

mchipser wrote:
I am trying to configure my stack of GS752TXS to use one DHCP server across 3 VLANs. I don't see an option to add a DHCP helper address. I read on a review a user was also unable to find this but used a workaround by trunking the port with the DHCP server. I tried this but my DHCP server still did not provide addresses to items outside of the PVID. I then contacted Netgear support and they said I needed to trunk it to a PVID not on a VLAN like 99. This did not work either. Anyone know how to work around this?


Yep, I did the trunking thing. Tagged all the VLANs and set the default route from the box over one of them and the others had no default route, turned off DNS servers on those interfaces and unchecked all bindings except IPv4 and definitely uncheck the "Register this connection in DNS" on the advanced page or you'll have stupid issues with the clients trying to connect to interfaces with either no routes or no services. Did this with two domain controllers that have DHCP and DNS on them as well.

I also tried manually putting an ip helper command in the config (using syntax from other netgear switches)...ummm yeah, that definitely did nothing. :-)

Hope that helps!

Mark
Occasional Contributor
Posts: 7
Registered: ‎2011-07-28

Re: GS752TXS DHCP Helper address

I have a number of VLANs on our GS752TXS stack configured, some on core (switch routed) networks and some on individual firewalled networks.  From what I could tell, there is no built in DHCP relaying or serving functionality in the GS752TXS firmware.  I ended up trunking each VLAN that we run DHCP on to a Linux server running dhcrelay, to forward the DHCP requests to the dhcpd server.  The basic idea is:

 

- All VLANs are trunked to a CentOS Linux relay server, each VLAN then has a virtual interface on the relay host, including switch-routed VLANs which the stack is the gateway for

- dhcrelay is set to listen to each virtual interface and forward requests to the actual central DHCP server

- DHCP server has subnet definitions (distinguished between each other by IP range) for each subnet

 

You could also skip the relay host and give the DHCP server virtual interfaces on each VLAN as well.  Either way be mindful of any security implications, esp. if you are mixing othewise isolated subnets, and construct your firewall rules appropriately.  Overall the setup works great, although dhcrelay (from CentOS 6 distribution) has crashed a couple times in the past 1.5 years or so.

 

Rob

 

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