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DHCP Broadcasts across WAN

Posted on 2012-12-27
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Last Modified: 2013-01-14
I am bringing up a new WLAN environment and all site LWAP's will receive their DHCP address from the main site that houses the WLAN controllers. I have setup a /24 for the controllers and the LWAP's.

I need some verification and or advice on how I can ensure when a new AP is plugged in that it's DHCP broadcast is sent over the WAN link to the DHCP server here. Seeing as how Routers break up broadcast domains that is a problem, but we have ip helper-address for this.

As it is now, I can ping across the WAN link to the /24 and DHCP server. Now if I create a new vlan interface on the core switch at the other location and set the ip helper-address on it, ping dies and I can no longer reach the /24

I somehow need this because once I start plugging in AP's and trunking ports to the native /24 vlan in question they will need to know how to reach their intended DHCP server.

I am somehow missing something
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Question by:dswope79
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by:rauenpc
ID: 38724014
It would be helpful if you posted the relevant configs. In General, you should only need the helper address. Things are slightly different depending on what mode your AP's are in. If they are in HREAP or Flex-connect you will have multiple vlans at the remote side which all will likely need a helper address pointed to a DHCP server with the appropriate pools. However, if they are in local mode where everything is tunneled back to the controller, all vlans exist at the core site with the WLC. Only those vlans will need helper addresses.

If all pings stopped when you created the new vlan, I would guess that there is some type of IP overlap - This could be a duplicated subnet or even two subnets with overlapping host ranges such as 192.168.1.0/24 overlapping 192.168.0.0/23.
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dswope79 earned 0 total points
ID: 38724120
These will be in HREAP mode.

I'm going to make Cisco TAC look at this, I showed them yesterday everything and how I have routing up between all sites to this /24 the WLAN Controller sits on.

I actually had one guy tell me yesterday all was well in my config and that the broadcast would go out across the WAN which isn't going to happen without some form of an ip helper
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by:rauenpc
ID: 38724143
Sounds good. If you get sick of waiting on TAC, feel free to post configs and "show ip route" on the devices in question.
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Author Closing Comment

by:dswope79
ID: 38773846
Created L2 network for each site for the AP's and the controller, got all the L2 and L3 issues out of the way. This question can be deleted.
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