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Community Member

DHCP with option 43

hello

I have come across DHCP with option 43, but i have no idea what it is and how it is configured. Anyone to assist?

Thanks

D

13 REPLIES
Cisco Employee

Re: DHCP with option 43

Hi Toy,

Using DHCP option 43 you can return the controller ip address in DHCP offer packet which will let the AP to discover the controller and ap will then start the join process.

Check this link for more details

http://www.cisco.com/univercd/cc/td/doc/product/wireless/control/c44/ccfig40/c40lwap.htm#wp1105242

This link will guide you step by step to configure DHCP option 43

http://www.cisco.com/en/US/products/hw/wireless/ps430/prod_technical_reference09186a00804fc3dc.html#wp125304

HTH

Ankur

* Please rate all helpfull post.

Community Member

Re: DHCP with option 43

Hi, thanks for the info. My DHCP server is a Cisco 2621XM router. ow do i configure option?? on a router(if necessary).

Thanks

D

Cisco Employee

Re: DHCP with option 43

Hi Toyi,

Yes you can configure 2600 router for option 43.

Can you update which AP you are using cause option 43 for AP 1010 is configured in different way then LWAPP converted APs.

Regards,

Ankur

Re: DHCP with option 43

hi ankur...

will you tell me what are the components used for wireless network?

what is the controller?

some body ask me is cisco aironet need controller and one more thing that i forgot so what is that?

regards

Devang

Cisco Employee

Re: DHCP with option 43

Hi Devang,

For wireless network you need a wireless node like laptop, printer, scanners etc etc and an access point which is connected to your infrastructure switch. It's just an extension to your lan with air media in between your node and switch.

Now think of a situation where you have hundreds and thousands on access point on roof top and ceilings and other places and you need to configure and troubleshoot it one by one is a very tough job. Controller give you an ease to access all your APs centrally and also troubleshooting and configuration becomes easy.

There are lot more benefits in using controller the nusing autonomous access points and that is the reason industries are slowly moving towards centralize architecture.

Cisco Aironet can be used in autonomous mode where you do not need controller and it is merely an IOS AP and need to be configured and troubleshooted individually but same aironet AP can be converted in light weight ap which will join the controller and then can be configured and troubleshooted from controller for all and any ap which had joined that controller. If we want any Ap to be a part of centralize architecture it need to be converted from IOS AO to LWAPP AP.

There is lot more to say and put here but I tried to put in brief and keeping the explaination in short.

HTH

Ankur

Re: DHCP with option 43

hi ankur...

thank you very much for your reply with lots of information... can you send me the link or can you send me some documents on my email id because i am new to this wirless network and we just have purchese the 1240AG for our lab so i need more and more detail so please help me by sending links or some good documentation...

regards

Devang

Cisco Employee

Re: DHCP with option 43

Hey Devang,

If you are using 1240AG access point in autonomous mode i.e without controller check this link

http://www.cisco.com/univercd/cc/td/doc/product/wireless/airo1240/index.htm

If you are usning controller to manage this and configure access points then have a look at this link which will guide you lot of stuff about how to configure controller

http://www.cisco.com/univercd/cc/td/doc/product/wireless/control/c44/ccfig40/index.htm

HTH

Ankur

* Please rate all helpfull post

Re: DHCP with option 43

hi ankur...

thank you very much for your response...

ankur from discussion forum i came to know that APs are layer1 and layer2 devices...

but still i want one things more... why do we need to creat subinterfaces on radio as well as fastethernet interface...?

we can directly connect fastethernet port to switch or router and instad of creating subinterface on AP's fastethernet we can creat subinterfaces on Router... same as our normal intervlan routing...so why do we need subinterfaces on AP's Fastethernet port...?

scott reply me with good explenation but still i want to know it more from you...

regards

Devang

Community Member

Re: DHCP with option 43

Hi Devang,

Creatio of sub-interfaces on FastEthernet and Dot11Radio interfaces are for a purpose of multiple SSID support. Those pairs of sub-interfaces (one from Fast and one from Radio interfaces) are placed into one bridge-group.

Think about it. If your WLAN environment supports multiple SSID, how can you differentiate between the traffic? Here is where sub-interfaces come into rescue.

There is a [logical] link between VLAN, SSID, Fast sub-int and Dot11Radio sub-int. Once user sends traffic on SSID A, this traffic is placed in relevant Dot11Radio sub-interface and transparently switched to Fast sub-int. Dot1Q tag is inserted and a frame is forwarded to you network infrastructure on a specific VLAN.

It is upto to your network devices to decide how to forward this traffic or apply security policy.

HTH,

David

Re: DHCP with option 43

hi david...

thanks for your reply...

okay we creat dot1q for the radiointerface to have more SSID... but we can use the Fastethernet port as trunk instad of creating any subinterface on it... as its trunk it is going to carry all the information...right...now i will configure the intervlan routing on the router connected to the fastethernet port of the AP...right... so can you give me specific reson for creating subinterface for the fastethernet port...

regards

Devang

Cisco Employee

Re: DHCP with option 43

Hi Devang,

Let me try to out in very simple explaination taking an example ofr 2 switches and later we will replace the second switch with access point.

Suppose you have 2 switches one doing inter vlan routing and another connected to it via trunk interface. Now the second switch has many physical interfaces on which you can connect your machines. Machines don't know anything about which vlan they belong to so as and when the traffic hits the physical interface it get to know which VLAN it belong to and the it passes via the trunk and layer 3 switch will do intervlan rouitng.

Now replace the seocnd switch with an access point where you do not have multiple physical interfaces and just a single radio on which multiple machines will connect. As radio provides a physical termination point to all wireless nodes , now in this scenario how and who will differentiate the 2 different wireless laptops belongs to which VLAN. Now for that you have something known as SSIDs but switch above will not understand SSIds and neither trunking protocol understand that so you have to have VLAN mapped to SSIds now how you can MAP VLANS to SSID as VLANs must be associated to physical/logical interfaces and that is the reason the subinterfaces which are mapped to VLANs and now cause the VLANs are associated to subinterfaces and if we MAP the subinterfaces to SSIDs any wireless nodes hitting the radio with particualar SSID will get assigned to that VLAN.

I hope I am able to explain in simpler terms.

Regards,

Ankur

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Community Member

Re: DHCP with option 43

Devang,

Creating sub-interfaces IS trunking :-)

Users terminate on Dot11Radio interface, how can you relay this fact to your switches if you have only one logical link? How can you differentiate between user connected to SSID A and user connected to SSID B?

By creating matching sub-interfaces on Fast and Radio interfaces you create a link through Access-Point. You put both subs into same bridge-group and this way user connecting do particular sub-interface on Dot11Radio interface will be switched to particular sub-interface on FastEthernet interface.

For example: SSID A is for regular users and SSID B is for guests, which should have limited access. SSID A is binded to VLAN 10 and Dot11Radio0.10 / FastEthernet 0.10 interface are created (and placed into bridge-group 10). SSID B is binded to VLAN 20 and Dot11Radio0.20 / FastEthernet0.20 interfaces are created (and placed into bridge-group 20).

Now on you distribution switches you create Interface VLAN 10 with no restrictions and you create Interface VLAN 20 with ACL attached to it.

HTH,

David

Re: DHCP with option 43

hi david...

thanks for your reply...but few more discussion on it... so please reply me...

so whatever i understand that...

by creating subinterfaces on both radio and Fastinterface for appropriate channel, you are trying to keep your traffice isolated from each other...

here multiple subinterfaces work as seperate ethernet interface ... which are also connected to the same vlan on the switch as on AP...

i mean you have vlan3 on AP and subinterface fastethernet 3 which is connected with the layer3 subinterface3...right...?and by defining the accesslist on subinterfaces you provide appropriate access to perticular vlan user...

now one more sentence from your reply is..."by creating matching suinterface on fast and radio interface you create a link through access-point" it means here you are idirectly you forward the traffic of vlan3 which is configured with radiosubinterface0.3 to the appropriate fastethernet subinterface 0.3...so other vlan traffic is also remain isolate... right? now traffice from AP's fastethrnet to Layer3/Layer2 device will passtrhough the trunk link and which is logically divided into the perticular sublink as per vlan number...right? if this is true then...

as we know vlan traffic is isolated from each other it means one vlan traffic is not heared by other vlan... so we can use the Fastethernet port of the AP as trunk and we are not going to creat the subinterface right...then also it should work... as we have connected it to layer3 and we have configure subinterface on it...

regards

Devang

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