Wireless AP

Answered Question
Oct 22nd, 2006
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Hi, hope you could help me with my wonderings, in our network we have cisco switch 2900 48 port, one of its port is connected to a AP, and the rest is going to production. everytime i connect to wireless i recieved a different segment IP address compare to wired. thanks

Correct Answer by jlkeys about 10 years 9 months ago

Wherever you're performing intervlan routing, you would need to use the ip helper-address command to re-direct DHCP requests to the DHCP server for the appropriate subnet.


So, If your DHCP server (with your 3 scopes configured) is on VLAN 1 with address 192.168.1.10, your config where you're performing the intervlan routing would need to include ip helper-address x.x.x.x for each interface:


int vlan 1

ip address 192.168.1.1 255.255.255.0

ip helper-address 192.168.1.10


int vlan 2

ip address 192.168.2.1 255.255.255.0

ip helper-address 192.168.1.10


int vlan 3

ip address 192.168.3.1 255.255.255.0

ip helper-address 192.168.1.10


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devang_etcom Sun, 10/22/2006 - 10:39
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will you please explain your network design and connectivity...as well as your DHCP server location... also about VLAN information...


regards

Devang

cool_mhar04 Sun, 10/22/2006 - 19:24
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weve got only one dhcp server on the site, can you be able to help me supposed, a 2900 series switch segmented into a couple of vlan, and these vlan talk to each other using the router, considering one of my port is a member of vlan2 is directly connected to my only dhcp on the site. We all know that evey vlan has the different subnets, how am i going to do to cater those subnets accordingly. I had created a different scope of subnets to be leased, according to my number of vlan, my aim for example vlan 4 i need this port member to be recieving 172.19.20.0 sybnets, please help what would be my configuration. Thank you

mgreenbaum Tue, 10/24/2006 - 11:56
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Verify that the AP isn't issuing the DHCP. The APs come with the option for them to be the DHCP server. Once you have done that, make sure that the AP sits in the VLAN that you want all wireless to be in, and it will request DHCP from that VLAN, ultimately giving you the subnet that you desire.

cool_mhar04 Tue, 10/24/2006 - 17:50
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Hi;


One more thing sir, suppose i have 1 switch and one router, the switch has 3 vlans, and i got only one dhcp server that was connected unto that same switch, we all know that vlans are segmented to a different subnets, supposed i got scope of 192.168.100.0, 192.168.200.0 and 192.168.300.0 this are networks, and I want my DHCP server scope 192.168.200.0 network block to be serving Vlan 3 member, how am i going to do that, do i have something to configure on my switch? or to my dhcp server itself? thanks

scottmac Tue, 10/24/2006 - 18:11
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You are not getting the same IP address because your wireless NIC has a different MAC address then your wired card.


DHCP tracks the leases (and provides controls, like reservations) based on the MAC of the NIC. Different MAC, different address and config info.


DHCP is also initiated by a broadcast from the client: The first device to see the broadcast will be the first to respond. If your AP and / or router are first to see it, or are more available from a procesing standpoint, they will provide the address ahead of the legitimate server.


Probably the easiest way to find out what's happening is to load Ethereal (www.ethereal.com ... now called wireshark ... something like that... it's free)on your laptop and follow the progress of your client's DHCP request and the various server's responses.


If you get a trace and don't understand what you see, post it up and we'll take a look.


Good Luck


Scott


cool_mhar04 Tue, 10/24/2006 - 21:26
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So it means sir, if my dhcp server is connected to VLAN 1, and the rest of my vlan's are going to our production, its not possible for me to make vlan 2 to lease only scope 192.168.200.0 and vlan 3 only for 192.168.300.0 network,.. they would all recieve a variety of ip address that are defined on all of my scopes, whoever asked for a new IP address to my DHCP?, no way for my configuration to appropriately alot an ip scope address specifically to one vlan. Thanks

Correct Answer
jlkeys Wed, 10/25/2006 - 02:35
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Wherever you're performing intervlan routing, you would need to use the ip helper-address command to re-direct DHCP requests to the DHCP server for the appropriate subnet.


So, If your DHCP server (with your 3 scopes configured) is on VLAN 1 with address 192.168.1.10, your config where you're performing the intervlan routing would need to include ip helper-address x.x.x.x for each interface:


int vlan 1

ip address 192.168.1.1 255.255.255.0

ip helper-address 192.168.1.10


int vlan 2

ip address 192.168.2.1 255.255.255.0

ip helper-address 192.168.1.10


int vlan 3

ip address 192.168.3.1 255.255.255.0

ip helper-address 192.168.1.10


cool_mhar04 Wed, 10/25/2006 - 03:36
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Great!, this is a real help, its working already, youre the man! ...:D, i had started configuring it..


To all who reply on my queries, and those who are answering other question.. I really appreciate it, thank you so much guys!!


till next time!



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