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New Member

how does WLC switch packets?

Hi guys,

Can you help me with the basic of switching process at the WLC? Bear me with this configuration:

For instances, the WLC is configured with this configuration:

Interface nameVLANIP Address / MaskPorts *)
Interface Management120192.168.120.1 /120

Primary: port 1

Dynamic interface /WLAN Interface10192.168.10.1 /24

Primary: port 1

* the WLC using only 1 distribution port

1. Traffic from wireless tunneled from AP to WLC and The traffic arrives at port 1 of the WLC.

2. WLC checks the packet's destination IP address and determine wheter the destination of that packet is for wireless or wired host.

Q-1: How can WLC knows the which destination address belongs to wired host and which destination address belongs to wired host?

3. If the destination address is for wired networks,

Q-2: how WLC knows what VLAN he should tag the packet, since the WLC only knows this 120 and 10 VLAN numbers, he don't know more that.

Thank you guys

Everyone's tags (3)
2 ACCEPTED SOLUTIONS

Accepted Solutions

how does WLC switch packets?

If the packet is destined for a wireless host, the WLC can do a lookup in the MSCB ( Mobile Station Controll Block).

If the WLC does not have the client in it's MSCB, it would forward the packet to the wire in the VLAN the sending client resides in.

HTH,
Steve

-----------------------------------------
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HTH, Steve ------------------------------------------------------------------------------------------------ Please remember to rate useful posts, and mark questions as answered

Re: how does WLC switch packets?

ok, let's try it this way.

The client is 192.168.10.5, and it is sending a packet to 192.168.15.26.

client <---> AP <----capwap tunnel---> WLC <---wire in VLAN 10.

Between the AP and the WLC, the packet has a CAPWAP header put on it.  the WLC removes the header and sends the packet to the wire in the VLAN the client is in.  From this point, the packet follows normal routing procedure for the VLAN.

HTH,
Steve

-----------------------------------------
Please remember to rate useful posts, and mark questions as answered

HTH, Steve ------------------------------------------------------------------------------------------------ Please remember to rate useful posts, and mark questions as answered
17 REPLIES

how does WLC switch packets?

If the packet is destined for a wireless host, the WLC can do a lookup in the MSCB ( Mobile Station Controll Block).

If the WLC does not have the client in it's MSCB, it would forward the packet to the wire in the VLAN the sending client resides in.

HTH,
Steve

-----------------------------------------
Please remember to rate useful posts, and mark questions as answered

HTH, Steve ------------------------------------------------------------------------------------------------ Please remember to rate useful posts, and mark questions as answered
New Member

how does WLC switch packets?

Sir, what layers do the WLC checks to determine where it should forward the packet? is it L2 or L3 addresses? sorry I loose this one..

how does WLC switch packets?

Lets follow the packet ..

When the paket arrives at the WLC the WLC rips off the CAPWAP headers and places the packet in the wired interface the WLAN is mapped to. The packet then exits the WLC and hits your switch. Then normal switch/route rules apply. If the MAC is not on that subnet it will then send it to the gateway. The gatway will look at the ip address and then route that puppy ...

Make sense?

__________________________________________________________________________________________ "Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin ___________________________________________________________
New Member

how does WLC switch packets?

Thank you Sir, finally got it!

Many thanks sir for your patience

how does WLC switch packets?

You have to remember that the AP traffic is tunneled , whereby the client traffic is contained within and never touches your switch fabric. The client traffic doesnt get unwrapped until it hits the WLC. After which point the WLC will then take the packet and apply to the proper wired side interface . After that point its sent up to the router.

make sense?

__________________________________________________________________________________________ "Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin ___________________________________________________________

how does WLC switch packets?

Steve -- Are you saying that the WLC will round the packet back out to the other wireless client without touching the switch ?

__________________________________________________________________________________________ "Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin ___________________________________________________________

Re: how does WLC switch packets?

it should, yes.  The WLC would know the packet is destined for one of it's clients.  no need to send that packet out to the wire.

HTH,
Steve

-----------------------------------------
Please remember to rate useful posts, and mark questions as answered

HTH, Steve ------------------------------------------------------------------------------------------------ Please remember to rate useful posts, and mark questions as answered
New Member

how does WLC switch packets?

Umm, I can't clearly understand your meaning sir.

After which point the WLC will then take the packet and apply to the proper wired side interface . After that point its sent up to the router.

make sense?

Are you saying that the dynamic interface that I've created is used by the WLC to determine that 192.168.10.x is on wired networks?

Re: how does WLC switch packets?

ok, let's try it this way.

The client is 192.168.10.5, and it is sending a packet to 192.168.15.26.

client <---> AP <----capwap tunnel---> WLC <---wire in VLAN 10.

Between the AP and the WLC, the packet has a CAPWAP header put on it.  the WLC removes the header and sends the packet to the wire in the VLAN the client is in.  From this point, the packet follows normal routing procedure for the VLAN.

HTH,
Steve

-----------------------------------------
Please remember to rate useful posts, and mark questions as answered

HTH, Steve ------------------------------------------------------------------------------------------------ Please remember to rate useful posts, and mark questions as answered
New Member

how does WLC switch packets?

Aha! I get it sir...

So the WLC tags all packets that is came from wireless with VLAN 10 whenever the packets is need to go to wired networks. It is from the packet's destination address the WLC knows if the packets belongs to the wired networks. If the packet belongs to wired networks, the WLC just tag it with VLAN 10 and send it to the neighboring switch.

By examining that VLAN tag, the neighbouring switch will decide which interface vlan responsibles for processing that packets and will decide whether the packets needs to routed or it just need to forward it to another ports.

how does WLC switch packets?

In this scenario that is correct.  To expand on that a bit, the WLC will tag the packet for the interface that the WLAN is linked to.

HTH,
Steve

-----------------------------------------
Please remember to rate useful posts, and mark questions as answered

HTH, Steve ------------------------------------------------------------------------------------------------ Please remember to rate useful posts, and mark questions as answered
New Member

how does WLC switch packets?

Aha, I see it now.

Another question sir please..

If you saying the WLC will tag the packet for the interface that the WLAN is linked to, may I know what's the IP address and subnet mask and Default-gateway address of that dynamic interface for?

If I configure my laptop using different IP's subnet than the dynamic interface's subnets, for instance 192.168.20.1, and ping to IP address 192.168.20.2.

are WLC still forwards and encapsulates my traffic using the VLAN 10 without considering my IP's is in different subnet than what is configured to the dynamic interface sir?

Thank you sir

how does WLC switch packets?

The WLC needs to be aware of the IP address of the VLAN, so that if a client roams between WLC, it knows if it is a L2 roam to pass the MSCB entry.  Or if it's a L3 roam, and it needs to anchor the client.

HTH,
Steve

------------------------------------------------------------------------------------------------
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HTH, Steve ------------------------------------------------------------------------------------------------ Please remember to rate useful posts, and mark questions as answered
New Member

how does WLC switch packets?

Umm.. That's too big for my thought sir.. I still not study the multi controller roaming process..

But, are you saying that the IP address of the dynamic interfaces / WLAN interfaces / VLAN interaces in the WLC is for the WLC itself to see if the clients doing L2 roams or L3 roams sir?

Re: how does WLC switch packets?

That is correct. The WLC is a layer 2 device only.

Steve

Sent from Cisco Technical Support iPhone App

HTH, Steve ------------------------------------------------------------------------------------------------ Please remember to rate useful posts, and mark questions as answered
New Member

how does WLC switch packets?

Okay sir. Thanks for the explaination.

Glad to have you here sir!

Cisco Employee

how does WLC switch packets?

Q-1: How can WLC knows the which destination address belongs to wired host and which destination address belongs to wired host?

WLC does proxy arp for all of its wireless client using its management interface, for no arp it broadcasts the packet to upstream which in turn forwarded to wired interface for that vlan.

Q-2: how WLC knows what VLAN he should tag the packet, since the WLC only knows this 120 and 10 VLAN numbers, he don't know more that.

WLC has got vlan interface IP on each of its interfaces, its kinda L3 interface with no intervlan routing and gateway residing outside the WLC .

#The below is applicable irrespective of AP group, AAA override, IG.

all Dst L2 traffic is checked against MSCB before forwarding to wired, Dst L3 traffic should hit the source gateway irrespective of wired or wireless.

Src           Dst          Hit wire/gateway

w.less - L2   w.less - L2  No

w.less - L2   w.less - L3  YES

w.less - L2   wired - L2   YES

w.less - L2   wired - L3   YES

#For Wireless traffic received/transmitted at WLC, it doesn't tag packets anywhere between its receving AP to WLC(or vice-versa) until the capwap removed and ready to forward the packet to upstream switch at the WLC.

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