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New Member

ip helper-address and VLANs

I have a few 2948Gs and a 3560 multilayer switch. I have the VLANs on a 2948, which points to the 3560 as its default gateway. I have connection throughout, I'm able to ping the DHCP server from the any switch, however the ip helper-address command doesn't work unless I define a static route on our router that points traffic destined for a particular vlan to get there via the multilayer swtich. I don't understand why that static route on the router is necessary for ip helper, can anyone explain? I've tried using the multilayer switch and the router as the dhcp server's gateway, but neither help.

thank you,

Bill

  • Other Network Infrastructure Subjects
5 REPLIES
VIP Purple

Re: ip helper-address and VLANs

Hello Bill,

not sure if I fully understand your physical setup: your clients are using the multilayer switch as their default gateway, and the VLAN interfaces are configured on that multilayer switch, the 3560 ? When you talk about your router, I assume you do not mean the 3560 ?

Regards,

GP

New Member

Re: ip helper-address and VLANs

that's correct. The multilayer 3560 is uplinked to a 2811 router. The 3560 is on the 10.4.0.0 subnet, and all clients in that subnet, which includes the DHCP server, use the multilayer switch as their default gateway, 10.4.0.84. The other VLAN clients use the address, as defined on the multilayer switch, as their default gateway. For example, the 10.4.5.0 VLAN uses 10.4.5.1 as their default gateway.

Re: ip helper-address and VLANs

Bill,

Please paste the config from your 3560 switch and also a detailed discription of the topology. where is the DHCP server located.Also describe about the Router is post above.

regards,

-amit singh

New Member

Re: ip helper-address and VLANs

I've attached the 3560s config. The DHCP server is on the 10.4.0.0 subnet.

3560MLS --------------------- 2811Router

|

2948Switch

|

2948Switch - DHCP server here, 10.4.0.16/24gateway is 10.4.0.84

|

2948Switch - VLANs reside here

New Member

Re: ip helper-address and VLANs

i think i got this. I needed to reboot my dhcp server after changing its default gateway to the multilayer switch, rather than the 2811 router. It seems to be working fine now.

thank you

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