802.11 Clients Communication

[xZamalek]

Dears,

I have started to study wireless and there are some concepts confuses me What i Understand is that the client will obtain an IP like this way:-

-The client will send a DHCP request over the AIR to the AP , the AP will now send this data over capwap to the WLC, the WLC will relay this request to the address cofigured in the interface section on the WLC , my question is , when the the DHCP unicast offer goes back to the WLC , will it send this info back to the Client in a CAPWAP tunnel to the AP ?

2-If PC-1 wants to communicate with the IP Phone , the traffic will goes from PC-1 > WLC > Core Switch and then the core will forward it to the Iphone , will the return traffic from the IP Phone to the PC-1 will be Iphone Phone > Access Switch > Core > WLC-1 > PC-1 ? from which interface the core switch will have the arp entry for the client in vlan 10?

3-If PC-1 wants to talk to PC-2 , the traffic will goes to WLC-1 , what will WLC-1 will do ? will it send the traffic back via capwap tunnel to AP-1 ? how the WLC Will forward the traffic between clients in the same SSID ?

4-If clients in different SSIDs , if PC-1 in SSID sales , and PC-2 in SSID Engineering , how the traffic flow will be like ?

5-If we have flexconnect WLC and the AP local switch , will the DHCP from the client will be sent from the AP directly to the wired network over the trunk link ?

[Rasika Nayanajith]

1. "The client will send a DHCP request over the AIR to the AP , the AP will now send this data over capwap to the WLC, the WLC will relay this request to the address cofigured in the interface section on the WLC , my question is , when the the DHCP unicast offer goes back to the WLC , will it send this info back to the Client in a CAPWAP tunnel to the AP "

Yes, assuming AP in local mode, all communication (control & data frames) between AP & WLC are CAPWAP encapsulated.

2-If PC-1 wants to communicate with the IP Phone , the traffic will goes from PC-1 > WLC > Core Switch and then the core will forward it to the Iphone , will the return traffic from the IP Phone to the PC-1 will be Iphone Phone > Access Switch > Core > WLC-1 > PC-1 ? from which interface the core switch will have the arp entry for the client in vlan 10?

Yes, that is right.

Since vlan10 gateway defined on the core switch, you will see wireless clients ARP entries on that switch. Not on the access switch

3-If PC-1 wants to talk to PC-2 , the traffic will goes to WLC-1 , what will WLC-1 will do ? will it send the traffic back via capwap tunnel to AP-1 ? how the WLC Will forward the traffic between clients in the same SSID ?

Yes, AP in local mode has to forward all traffic to WLC.  AP can be in FlexConnect mode (for branch deployment) where data traffic terminates on AP itself without go to WLC.

4-If clients in different SSIDs , if PC-1 in SSID sales , and PC-2 in SSID Engineering , how the traffic flow will be like ?

Still the same principle applies, AP will forward it to WLC and then WLC take decisions where it need to forward

5-If we have flexconnect WLC and the AP local switch , will the DHCP from the client will be sent from the AP directly to the wired network over the trunk link ?

FlexConnect is mode of operation in AP. Once AP in FlexConnect you have two choices for SSID config. 

You can do either

1. Local Switching

2. Central Switching

In the Local switching scenario, wireless users' data will be terminated on AP, so when you configure  AP connected switchport as a trunk port, that traffic locally switch at branch switch. That traffic never go back to WLC

HTH

Rasika

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[xZamalek]

Hello Rasika,

Thank you so much for your clarifications , it's really useful.

-Regarding 2nd Point , will the core switch learn the MAC Address "of the client PC-1" from the port-channel configured towards the WLC ? did when the core switch sent an ARP request , this arp request was sent to the WLC and the WLC replied to the core switch on behalf of the client as the WLC already has the client association table with their MAC and IPs? or it works another way ? maybe the controller forwarded this ARP to the client it self via CAPWAP ?

-Regarding 4th Point , its really confuses me when will the WLC will need to send the traffic to the wired network and when to not , so for example , if both SSIDs are configured on the WLC , each SSID has it's interface with a VLAN , on traditional switched network the intervlan routing will be done on the core switch , now my question is , how the WLC will make an Inter SSID Routing ? will it just look it's client table , find that the destination is attached to a specific access point which the WLC already have a capwap with and send the traffic without going to the wired network at all as both vlans and interfaces are configured locally on the WLC ?

[Rasika Nayanajith · Accepted solution]

-Regarding 2nd Point , will the core switch learn the MAC Address "of the client PC-1" from the port-channel configured towards the WLC? did when the core switch sent an ARP request , this arp request was sent to the WLC and the WLC replied to the core switch on behalf of the client as the WLC already has the client association table with their MAC and IPs? or it works another way ? maybe the controller forwarded this ARP to the client it self via CAPWAP ?

ARP Table maintained in the core switch, not in WLC. WLC keeps a client database, not an ARP table like a traditional switch.

Regarding 4th Point , its really confuses me when will the WLC will need to send the traffic to the wired network and when to not , so for example , if both SSIDs are configured on the WLC , each SSID has it's interface with a VLAN , on traditional switched network the intervlan routing will be done on the core switch , now my question is , how the WLC will make an Inter SSID Routing ? will it just look it's client table , find that the destination is attached to a specific access point which the WLC already have a capwap with and send the traffic without going to the wired network at all as both vlans and interfaces are configured locally on the WLC ?

Remember WLC is like a L2 switch, inter-vlan routing is not performed at WLC level, it has to send that traffic to Core switch on the trunk and core switch performing routing decisions. When traffic comes to WLC with appropriate vlan tags in trunk, WLC will take that information to create of CAPWAP tunnel back to AP.

Also, note that CAPWAP is a simple UDP header that encapsulates the original IP packet. CAPWAP header src will be WLC mgt & dst IP would be AP mgt IP address if traffic is downstream from WLC -> AP. Original source and dst IP is within the inner packet and unchanged during transition.

HTH

Rasika

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