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WLC redundancy design

I have the following wireless design but not sure whether the wlc redundancy will work a not.

  • 100 remote sites
  • 25-45 APs per remote site
  • 1 5508 WLC per site
  • 2 5508 WLC at DC
  • each site has a 5Mbps link to DC
  • wireless clients connect using 802.1x
  • RADIUS server located at each site
  • DHCP server located at each site

The 2 WLCs at the DC are supposed to be the backup controllers for the local controllers when they fail. The APs will be configured in local mode and have primary and backup controllers configured. HREAP has been ruled out due to its many limitations.

From here onwards please correct me if i am wrong.

If one of the local controllers fail, all the APs at that remote site will fall back to the backup WLC at the DC. As the DC WLC will not be able to differentiate the locations of the connecting APs, I have to use another IP address range to cater for these APs. Thus the APs will no longer reside in the local WLAN subnet that i originally cater for them.

For the wireless client's IP address, is it possible for me to determine the site that the client resides in based on the 802.1x account? If possible, can i then reroute the DHCP request to the local DHCP server at the site itself. I am hoping this is feasible so that i do not have to open up another IP address range at the DC side to cater specially for these wireless clients.

For data traffic travelling from the wireless clients to the local site servers, how does the data travel? My understanding is that the data will travel from the wireless client to the DC WLC via a LWAPP tunnel. So on the DC WLC, the  traffic will be forwarded to the core switch and then to the router. the router will then route the data back to the remote site, provided the routing table is populated properly.

Each remote site has a link to the internet but the DC does not. so i wonder how will the wireless internet traffic be routed when the local controller fails? when the internet traffic reaches the DC router, how will it know which remote site to forward it back to?

All advice and suggestions are welcome.

2 REPLIES

Re: WLC redundancy design

1.If one of the local controllers fail, all the APs at that remote site  will fall back to the backup WLC at the DC. As the DC WLC will not be  able to differentiate the locations of the connecting APs, I have to use  another IP address range to cater for these APs. Thus the APs will no  longer reside in the local WLAN subnet that i originally cater for them.


ANS: when the  remote wlc fails the Ap fails over ot the  backup wlc at DC but it will still retain the IP address from the local switch at the remote site ( From  the DHCP server) confgure, so ip address of Ap will not change. ( i hope you are not meaning wlan user subnet )

2.For  the wireless client's IP address, is it possible for me to determine  the site that the client resides in based on the 802.1x account? If  possible, can i then reroute the DHCP request to the local DHCP server  at the site itself. I am hoping this is feasible so that i do not have  to open up another IP address range at the DC side to cater specially  for these wireless clients.

ANS: If you are not using HREAP then as soon as the AP at remote site fails over to the  DC wlc  it will lose it AP Group configuration from remote site wlc and takes the wlan and default vlan mapping at  DC site ( hence losing  Remote site specific differentiation)  unless remote ap once failed  over is added  in the Ap group  - ( which would mean manual intervention)

3.For  data traffic travelling from the wireless clients to the local site  servers, how does the data travel? My understanding is that the data  will travel from the wireless client to the DC WLC via a LWAPP tunnel.  So on the DC WLC, the  traffic will be forwarded to the core switch and  then to the router. the router will then route the data back to the  remote site, provided the routing table is populated properly.

ANS : The data will be tunneled to the DC wlc via lwapp tunnel decapsulated and will  put on local core switch if traffic is meant for local  routng i will be routed , if it  is destined for any remote server lets say and we have a route in the DC network of  remote server then it waill be routed back to the remote network not other wise.

4.Each  remote site has a link to the internet but the DC does not. so i wonder  how will the wireless internet traffic be routed when the local  controller fails? when the internet traffic reaches the DC router, how  will it know which remote site to forward it back to?

Ans: This answer is related logically to 2 answer, it will not be able to route internet traffic

Sri

Cisco Employee

Re: WLC redundancy design

WOW!!! Srini.. lemme be frank.. this question was posted on 3rd Nov and stayed untouched and unanswered for a month!! really appreciated!! to be frank i did not go through the post since it was very lengthy.. many may hav tot the same!! ... But u did it!! +5

Regards

Surendra

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