As part of SP-wifi solution, Cisco wireless is providing some Key features
NOTE- Central-DHCP, DNS Override and NAT/PAT can be enabled at three different levels – on WLAN (local-switching), on Flex AP.
Point to remember-- All three features [central-dhcp, dns override and nat/pat] by default will be enabled on PPPoE AP when WLAN is configured as local-switching and cannot be disabled or deleted.
Let’s discuss in detail.
Wireless client gets IP address from central-site even though wlan is configured with Local-switching. Before this feature there was no way to control DHCP addressing from central site for local-switched wireless clients. If the feature is enabled then the Cisco AP sends DHCP packets to WLC using CAPWAP, same as central-switching wlan. When client gets IP Address, AP starts local-switching for DATA traffic.
When local-switching and Central-DHCP is enabled, Cisco AP will do Authentication and DHCP for wireless client at Central-site (same as central-switching) and data traffic (except DHCP) will be local-switched.
NOTE– Local-auth on Flex AP is NOT supported when Central-DHCP is enabled.
NOTE– DHCP_Required option has to be enabled before enabling Central-DHCP on wlan. DHCP_Required is will be enabled internally on PPPoE AP if wlan is local-switching. DHCP_Required will be enabled on non-PPPoE Flex AP and Flex-Group if Central-DHCP.
In the SP-wifi deployment with Central-DHCP in use, it’s very tough for an Admin to know DNS IP Address for each branch (when there are different ISP's at each branch) on and configure in the DHCP server at central site because when Central-DHCP option is configured and Cisco AP is doing NAT/PAT. Wireless client has to get DNS IP of local ISP.
This feature [DNS Override] will make Administrator’s life easy. In the SP-wifi deployment, Cisco AP gets IP address including DNS ip address from local ISP.
Wireless Controller comes to know about AP’s DNS IP Address when AP is joining wireless Controller. If the “DNS Override” feature is enabled then Wireless Controller will override the DNS IP Address when wireless client does DHCP.
In SP-wifi deployment where ISP line is terminating at Cisco AP and then Cisco AP should do NAT/PAT for wireless client traffic. This feature is very useful when wireless gets Private IP address and there is no device between AP and ISP that can do NAT/PAT for wireless client but it’s not limited to this kind of deployment. The feature can be enabled wherever Admin wants Cisco AP to do NAT/PAT for wireless client.
Currently manual configuration is not required on Cisco AP of NAT/PAT. It’s configured implicitly on the AP when client associates if NAT/PAT is enabled or AP is PPPoE AP.
As we discussed before, Central-DHCP, DNS Override and NAT/PAT can be configured at three levels – on wlan, on AP and on Flex group. Configuration on Flex AP is highest priority then Flex-Group and then WLAN.
There are three parameters to configure on Flex AP and on Flex-Group – Enable, Disable and Delete and Two parameters on WLAN – Enable and Disable.
NOTE– Configuration on higher level should be “Deleted” to take effect of lower level configuration. Example – If Flex AP is configured with Enable and if administrator wants to enable these features [central-dhcp, dns-override or nat/pat] then Flex AP’s configuration should be “Deleted” NOT “Disabled” to take effect Flex-Group configuration.
NOTE– As discussed earlier, all three features [Central-DHCP, DNS Override and NAT/PAT] are by default enabled on PPPoE Flex AP if WLAN is local-switching and the configuration cant be disabled or deleted.
Configuration on WLAN
------ >> Click on the “Central DHCP Processing” option.
When local-switching is enabled on WLAN and AP is broadcasting the WLAN then the WLAN entry will be created on the Flex AP to configure Central-DHCP, DNS Override and NAT/PAT.
NOTE – Currently there is NO option in 7.3 image to see on Flex AP that whether Central-DHCP, DNS Override and NAT/PAT configuration of Flex AP, Flex-Group or WLAN on GUI but CLI has it.
config wlan flexconnect local-switching <wlan_id> [enable | disable | central-dhcp | override]
config wlan flexconnect local-switching <wlan_id> central-dhcp [enable | disable | nat-pat]
config wlan flexconnect local-switching <wlan_id> central-dhcp nat-pat [enable | disable]
config wlan flexconnect local-switching <wlan_id> override option dns [enable | disable]
config wlan dhcp_server <wlan_id> <ip_address> required
IP Address of DHCP server. Configure 0.0.0.0 to use default interface server.
config ap flexconnect central-dhcp <wlan_id> <ap_name> [enable | disable | delete]
config ap flexconnect central-dhcp <wlan_id> <ap_name> [enable / disable] override dns [enable | disable] nat-pat [enable | disable]
config flexconnect group sp-group central-dhcp <wlan_id> [enable | disable | delete]
config flexconnect group sp-group central-dhcp <wlan_id> [enable | disable] override dns [enable | disable] nat-pat [enable | disable]
1. Show wlan <wlan_id>
2. Show ap config general <ap_name>
3. Show flexconnect group detail <flex_group_name>
(sp-wifi-wlc)show wlan sp-wlan | | Wi-Fi Protected Access (WPA/WPA2)............. Disabled Wi-Fi Direct policy configured................ Disabled EAP-Passthrough............................... Disabled CKIP ......................................... Disabled Web Based Authentication...................... Disabled Web-Passthrough............................... Disabled Conditional Web Redirect...................... Disabled Splash-Page Web Redirect...................... Disabled Auto Anchor................................... Disabled FlexConnect Local Switching................... Enabled flexconnect Central Dhcp Flag................. Enabled flexconnect nat-pat Flag...................... Enabled flexconnect Dns Override Flag................. Enabled ----------------xxxxx------------- (sp-wifi-wlc)show ap config general ap_3600 | | Flexconnect Central-Dhcp Values : WLAN ID PROFILE NAME Central-Dhcp DNS Override Nat-Pat Type ------- ----------------------- -------------- ---- ----------------- --------- ------ 12 spwifi True True True Flex-Group | | AP TCP MSS Adjust................................ Disabled Hotspot Venue Group.............................. Unspecified Hotspot Venue Type............................... Unspecified DNS server IP ............................. 22.214.171.124 ---------------xxxx-------------- NOTE– “Type” shows of which level config is being used. In above example Flex-Group config is being used for central-dhcp. (sp-wifi-wlc) >show flexconnect group detail sp-group | | Number of User's in Group: 0 WLAN ID SSID Central-Dhcp Dns-Override Nat-Pat 12 spwifi False False False | ----------------xxxx---------------
There is no new commands since the DHCP packet comes to wireless controller all old commands can be used.
1. Debug client <client_mac>
2. Debug dhcp [message | packet | service-port]
There is no debug command but we can troubleshoot using following commands
1. Show ap config general <ap_name> -------------- >> it will show the DNS ip of AP.
2. Show client detail <client_mac> -------------- >> it will show DNS ip on client and AP.
3. Show hosts ----------------- >> The command is used at Flex AP to check DNS IP on the AP.
4. Check DNS IP on the wireless client.
There is no command on wireless controller since the NAT/PAT is done at Flex AP. All most all IOS commands can be used to see or troubleshoot NAT/PAT issue on AP.
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For more information on Service Provider Wi-Fi supported features: