Inter-Subnet roaming - Traffic Paths

Answered Question
Jul 21st, 2009
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I have a question in regards to how a clients traffic is properly forwarded when it roams from one AP/WLC pair, to another AP/WLC pair.


See figure 11-3:

http://www.cisco.com/en/US/docs/wireless/controller/5.1/configuration/guide/c51mobil.html


How is it possible that traffic originating from the client, gets forwarded to VLAN y. The default gateway for the client is on VLAN x. Is there some function the WLC plays in forwarding the data of a foreign client, negating the gateway address(which is on VLAN x) it is attempting to use?



Correct Answer by jakew about 8 years 2 days ago

Don't over think it... what comes out of the controller upstream (on VLAN y) is an IP packet with a source IP (client) and a dest IP (wherever the packet is going). And what do routers do with IP packets? Ah yes, they route them. Note: the controller will put the L2 dest address as the mac addy of the default gateway for VLAN y.


Note that we recommend you use symmetric tunneling now, assuming your code version supports it. In 6.0, symmetric tunneling is all that is supported.

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Correct Answer
jakew Tue, 07/21/2009 - 17:23
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Don't over think it... what comes out of the controller upstream (on VLAN y) is an IP packet with a source IP (client) and a dest IP (wherever the packet is going). And what do routers do with IP packets? Ah yes, they route them. Note: the controller will put the L2 dest address as the mac addy of the default gateway for VLAN y.


Note that we recommend you use symmetric tunneling now, assuming your code version supports it. In 6.0, symmetric tunneling is all that is supported.

yuribank415 Tue, 07/21/2009 - 18:01
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Ah thanks for clearing that up for me. I will now be able to sleep tonight!


I'm glad Cisco is phasing out Asymmetric tunneling.


Symmetric tunneling makes a lot more sense, avoiding problems with RPF checks and such.



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