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WLC Internal and External DHCP

I am currently using the Internal DHCP component within my 5508 Controller with software version 7.0.166.0.  This seems to be working fine as the Vlan Routed interface connected to it via the Dynamic Trunk Port is functioning as l have the ip-helper command setup on this specific vlan interface..

My issue now is that we have a isolated ADSL Network which is configured off our Core 6513 but just as a Layer 2 Vlan so no traffic can be routed to other vlans.

With our new WIFI environment which consists of the 5508 Controller and numerous 3502 AP's we wont to utilize this ADSL vlan with our new WIFI environment..  This ADSL Vlan has a dedicated Linksys Router which is currently running DHCP and assigning addresses to clients at the moment..

What l want to do is configure the 5508 controller to use this ADSL vlan aswell but to also keep using the Linksys Router aswell for DHCP..

I have setup a new dynamic interface and added the ADSL Vlan ID to the Trunk port of the 5508 and also setup its own SSID.  But for some reason l cannot get both the internal and External DHCP servers to work at the same time ?  If l enable DHCP Proxy option on the 5508 the internal DHCP server works and when l disable DHCP Proxy the ADSL Vlan DHCP works through the 5508 but not the internal DHCP Server ??

Can l get both the internal and external DHCP servers to work in harmony or should l be focusing on using one method over the other ?

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Hall of Fame Super Silver

WLC Internal and External DHCP

I see you have the management on port 8 and everything else on port 1.  If you are trunking, make sure you only allow the management vlan on port 8 switchport trunk and only allow vlan 40, 410, 520 and 540 on port 1 switchport trunk.

-Scott
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21 REPLIES
Hall of Fame Super Silver

Re: WLC Internal and External DHCP

So you have dhcp running on the wlc for your internal network and you want I use the adsl router for dhcp for that network?

Sent from my iPhone

-Scott
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New Member

Re: WLC Internal and External DHCP

Yes Correct l want to still use the internal DHCP from the 5508 for specific Corp WIFI VLans and also utilize the isolated ADSL Vlan's DHCP Server aswell..

Hall of Fame Super Silver

Re: WLC Internal and External DHCP

Well in the dynamic interface that connects to your adsl subnet, did you specify the adsl router as the dhcp server. That setup should work, just seems like your missing something.

Sent from my iPhone

-Scott
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New Member

Re: WLC Internal and External DHCP

Hi Scott,

Yes the Dynamic interface has the ip address of the ADSL Vlan DHCP Server , l also tried adding it to the ADSL WLAN ID under the Advanced Tab where you can specify the "DHCP Server Override" option...  but with no luck

Hall of Fame Super Silver

Re: WLC Internal and External DHCP

Interesting... I'm wondering if the adsl router doesn't like the WLC requesting the dhcp instead of the client.  Why not just create a dhcp scope on the wlc for that subnet?

Sent from my iPhone

-Scott
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Hall of Fame Super Silver

Re: WLC Internal and External DHCP

You are doing LAG correct?

Sent from my iPhone

-Scott
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New Member

Re: WLC Internal and External DHCP

Hi Scott,

Currently not using link aggregation of this Trunk Port interface.. Should that matter ? 

Yeah true in saying to create another dhcp scope from the internal dhcp server from the 5508 but thought l could still possibly use the Linksys RV042 aswell ?

Hall of Fame Super Silver

Re: WLC Internal and External DHCP

So you just have port 1 connected to your core? I always have LAG enabled unless I specify SSIDs on different ports.

Sent from my iPhone

-Scott
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New Member

Re: WLC Internal and External DHCP

Yeah its something that will be done as a whole shortly through our Core.  We currently only have 1 5508 controller but have 2x6513's and was actually looking at dual attaching the 5508 to both 6513's is this possible ?

Anyway that could be another discussion topic to open aswell ??

Hall of Fame Super Silver

Re: WLC Internal and External DHCP

It would work if your running vss between the two chassis.

Sent from my iPhone

-Scott
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New Member

Re: WLC Internal and External DHCP

Something to look forward to when we upgrade our Core/IOS in the next few months..

Anyway back to the dhcp issue..  I will look into possibly creating another internal dhcp server scope for this L2 vlan..  But if we could get the Linksys Router working l would prefer that for the meantime..

Hall of Fame Super Silver

Re: WLC Internal and External DHCP

To use the WLC as a dhcp, you need to enable DHCP proxy as it is required. Your initial testing shows that the adsl doesn't work if the WLC is doing the proxy.  Knowing this, I don't think you will be able to get that to work since the WLC requires dhcp proxy and the adsl router requires that to be diabled.  You could compare the two by running a debug client with dhcp proxy enabled and disabled.

-Scott
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New Member

Re: WLC Internal and External DHCP

Thanks for your assistance scott..  Will configure another scope today for this other vlan and test..

Hall of Fame Super Silver

Re: WLC Internal and External DHCP

Keep me posted, that should work though.

Sent from Cisco Technical Support iPhone App

-Scott
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New Member

Re: WLC Internal and External DHCP

Will do scott cheers mate !!

New Member

Re: WLC Internal and External DHCP

Hey Scott l have just tried configuring another scope for the L2 Vlan but it doesn't seem to be working when l add the ip address of the management interface which is the internal DHCP Server to the dynamic interface of this adsl network l have setup l dont seem to get a ip address within this scope ?

I am just wandering seeing it is just a L2 vlan without a routed interface would this be the problem and would need to set this up with the "ip helper-address" of the management interface ?

Cheers SG

Hall of Fame Super Silver

Re: WLC Internal and External DHCP

You shouldn't need to use an ip helper and since you don't have a l3 interface you can't configure that. Do you mind posting your config so I can look at it.

Show run-config no ap

Sent from my iPhone

-Scott
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New Member

Re: WLC Internal and External DHCP

Hi Scott,

attached is config of the 5508 Controller

Hall of Fame Super Silver

Re: WLC Internal and External DHCP

SG,

On your wlan 2 ACMI-ADSL, you have DHCP Overide still enabled poiinting to your ADSL Router.  Remove that and it should work.  I will take a look at the rest of your config.

-Scott
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New Member

Re: WLC Internal and External DHCP

thanks scott !  Totally forgot to untick this !! 

Will re-test shortly..

Thanks again for your assistance, if you find anything else in the config you recommend let me know..

SG

Hall of Fame Super Silver

WLC Internal and External DHCP

I see you have the management on port 8 and everything else on port 1.  If you are trunking, make sure you only allow the management vlan on port 8 switchport trunk and only allow vlan 40, 410, 520 and 540 on port 1 switchport trunk.

-Scott
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