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DHCP Problem in Scenario 3 (Centralized Network Topology)

 
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LynxX



Joined: 29 Jun 2011
Posts: 22
Location: Sweden

PostPosted: Thu Mar 28, 2013 1:04 pm    
Post subject: DHCP Problem in Scenario 3 (Centralized Network Topology)

sHello support!

I have runned in to a DHCP problem in the Scenario 3 (Centralized Network Topology) - multiple network segments with one centralized
FirstSpot to serve all Hotspot sites.

The setup is like the picture in the manual on page 35.

The problem is that the client gets a faulty subnet mask.

My setup looks like this:

Patronsoft server to hub router is a 255.255.255.240 subnet
The client network is a 255.255.255.0 subnet

The list i filled in to the distrubuted network looks like this
Router IP Subnet Mask Gateway
10.126.60.1 255.255.255.0 10.126.0.33

I can ping the Router IP 10.126.60.1 and the clients gets a DHCP lease form the Patronsoft server, typically 10.126.60.145 (I can see it in the DHCP page).

When checking network traffic with Wireshark I discover that the Client gets a 255.255.255.240 subnet in the DHCP offer packet.

The server must have a 255.255.255.240 mask and the client subnets can have ranges from /23 to a /26 subnet.

Please advice

Best regards
Johan
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alan
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Joined: 26 Sep 2003
Posts: 4404

PostPosted: Thu Mar 28, 2013 4:07 pm    
Post subject:

So the problem is that client get the wrong subnet mask? Can you change (as a test) FirstSpot visitor side subnet mask to 255.255.255.0 also to see whether the problem persists?
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LynxX



Joined: 29 Jun 2011
Posts: 22
Location: Sweden

PostPosted: Tue Apr 02, 2013 7:39 am    
Post subject:

Hi support,

I did a fast test and yes, the visitor DHCP offer subnet mask is changed to 255.255.255.0 when changing Firstspot server NIC visitor side subnet mask.

I have now set it back to 255.255.255.240 again as the 10.126.0.0 subnet is in use.

I am grateful for fast assistance as we are late on the deployment of the Firstspot service.

BR/ Johan
Volvo IT
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LynxX



Joined: 29 Jun 2011
Posts: 22
Location: Sweden

PostPosted: Tue Apr 02, 2013 8:34 am    
Post subject:

As a test I have now set the visitor distrubuted network to:
Router IP Subnet Mask Gateway
10.126.60.1 255.255.255.240 10.126.0.33

Now I run in to a second problem.
When looking in the DHCP Discover packet:
Relay agent IP address: 10.126.60.2 (Cisco WLC interface address)

When looking in the DHCP Offer packet:
Router: 10.126.60.2

Problem:
Patronsoft DHCP Offer states the Relay Agent as Default Gateway for the client. I thought it should be the Router IP in the Distrubuted network variables?

BR/ Johan
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LynxX



Joined: 29 Jun 2011
Posts: 22
Location: Sweden

PostPosted: Tue Apr 02, 2013 9:10 am    
Post subject:

BTW - is there another forum as we have bougth a maint contract?
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alan
Forum facilitator


Joined: 26 Sep 2003
Posts: 4404

PostPosted: Tue Apr 02, 2013 9:37 am    
Post subject:

FirstSpot DHCP assume router IP and DHCP relay to be same IP.

Also, does 255.255.255.0 work well? You may want to simplify it and switch to this subnet at this moment.
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LynxX



Joined: 29 Jun 2011
Posts: 22
Location: Sweden

PostPosted: Tue Apr 02, 2013 9:48 am    
Post subject:

Hi support

There are several situations where the relay agent (stated in the DHCP request) and router (default gateway for client) is not the same. For example wireless networks with Cisco WirelessLanControllers. Will you change this or make it possible to use the gateway stated in "Router IP"?
If not, we, and several others will not be able to use Patronsoft as a guest solution.

255.255.255.0 is sent in the DHCP offer when I set the Client NIC to this subnet, but as the Client NIC is on a .240 subnet and the client subnets will vary (/23 to /26 subnets) I can not keep the .0 for several reasons.
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alan
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Joined: 26 Sep 2003
Posts: 4404

PostPosted: Tue Apr 02, 2013 10:16 am    
Post subject:

Yes, currently this is a limitation in our DHCP server. Can you change your Cisco router so that the DHCP relay and router IP remain the same?

Alternatively, FirstSpot can work with third-party DHCP server like Microsoft DHCP server or your router's DHCP server. Make sure you turn off FirstSpot DHCP server under Configuration Manager if you go this route.
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LynxX



Joined: 29 Jun 2011
Posts: 22
Location: Sweden

PostPosted: Tue Apr 02, 2013 11:43 am    
Post subject:

Okey - I have now looked in to the Cisco WLC. This unit acts as a DHCP Proxy (not a router) by default and therefore also the DHCP Relay.
It is possible to change this to DHCP Bridging mode.
But... then all WLC's must be changed to DHCP Bridge, just not the VLAN used.
This will probably be tricky to performe as we have approx 80 WLC's and a couple of 100's VLAN's in production today, and I am not sure what the impact will be.

I tested to remove the DHCP Proxy functionality on a test WLC and I now got a connection for the Guest Client.

Open cavets:
The DHCP scoop problem (see subnet mask issue)

It would be great if you could implement the feature to set the Router option to a specific value, as the DHCP servers of my knowlage got this option. Or is the recommendation to use an Microsoft DHCP services on the same server as Patronsoft is located?

BR/ Johan
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alan
Forum facilitator


Joined: 26 Sep 2003
Posts: 4404

PostPosted: Tue Apr 02, 2013 2:15 pm    
Post subject:

If you want to use one centralized DHCP server, yes you can try Microsoft DHCP server located in the FirstSpot machine.

We will consider your request in future update.
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LynxX



Joined: 29 Jun 2011
Posts: 22
Location: Sweden

PostPosted: Wed Apr 03, 2013 11:51 am    
Post subject:

Installing the MS DHCP server fixed both the subnet mask and DHCP Proxy problems.

BR/ Johan
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