Ip helper-address

[Patrick Michaud]

Hi all,

We've put in a Cisco 3550 a command "ip helper-address" on a vlan interface.

But when we connect a pc on the vlan 1 the DHCP, which is in vlan 2, its give it a good ip address.

When we try to disconnect from vlan 1 to put on vlan 2, we don't receive any ip address or the address is still an address of vlan 1.

Is there any Cisco command that we've not added in 3550?

Can you help us?

Thanks in advance.

[Sarbjit-2014]

Hi Patrick,

Not 100% sure what you mean, can you post your config. Also what does your DHCP scope look like ?

regards.

[Patrick Michaud]

Thanks to AllertGen and Sarbjit-2014.

Did you put "ip helper-address" at both vlan interfaces: No

Just on the vlan interface that is not on the same vlan of the DHCP...

We've made a Global Scope with two scopes for each vlan.

regards.

[Andre Neethling · Accepted solution]

If you have a global scope, the server might issue from that scope, and not the individual scopes you have configured below it. Try re-creating just the 2 VLAN scopes, with no global scope. This has worked for me before.

[Patrick Michaud]

Hi Andre,

Thanks for information.

I'll try it next week.

Thanks.

[Patrick Michaud]

Hi Andre,

My problem was my superscope. I've re-created two scopes and it works fine.

Thanks a lot.

[Andre Neethling]

It's a pleasure, and Thanks for coming back to us. By the way, this is not a cisco issue. It's the DHCP server. I'm guessing you're using a Microsoft DHCP server.

[AllertGen]

Hello, Patrick Michaud.

Did you put "ip helper-address" at both vlan interfaces? Did you configure your DHCP server for each vlan? For exapmle if you have 2 networks 192.168.0.0/24, 192.168.1.0/24 and your DHCP server configured with pool 192.168.0.0/23 you'll get IP address from a first network even if your client at the second. So at DHCP server you need to have a pool for each network.

Best Regards.

[Sarbjit-2014]

Hi Patrick,

Check your DHCP scope each scope should have a default gateway, corresponding to its own VLAN SVI I.P address.

Regards.

[Patrick Michaud]

Hi,

Yes, it's done.

Do I need to make an ip helper-address on each vlan?

The vlan2 has his own DHCP.

regards.

[Jon Marshall]

You don't need an ip helper-address on the vlan 2 interface because the DHCP server is in vlan 2.

When you moved the PC across did you do an "ipconfig /release" and "ipconfig /renew" on the PC.

If the PC is still not getting an IP then unless you have extra configuration on your switch in terms of acls etc. it is probably the DHCP server you need to look at.

Jon

[Patrick Michaud]

Hi,

Ipconfig commands doesn't work, so I'll look at DHCP.

Thanks Jon.

[Jon Marshall]

Just to clarify, the ipconfig commands are on your PC not the switch and you need to do them from a cmd window.

Jon

[narindergwalive]

Just go to cmd prompt on your pc and give a command "ipconfig/release and ipconfig/renew"

i hope it will work.