L3 intra-controller roam

[janesh_abey]

Hi folks,

I fully understand how Layer 2/3 roam function and role of EoIP in an inter-controller enviornment.L2 intra-controller roaming also pretty straightforward.

However, L3 intra-controller roaming is not very clear to me.Could someone throw some light on the matter pls?Also if you could point me to to a Cisco doco that would be great.

Thanks,

J

[Leo Laohoo]

http://www.cisco.com/en/US/docs/wireless/controller/7.0MR1/configuration/guide/cg_mobility.html

[Mady Gueye]

hi all,

someone can reponse me: L2 – Inter Controller Roaming support the web-authentication(if the client pass through one ap to another ap there’s not need to re-authenticate)?

please help me.

[Stephen Rodriguez]

Janesh,

     To make sure I understand.  You are wondering what will happen if a client roams to a different subnet, but stays on the same WLC, like AP Groups are in place.  correct?

If this is what we are discussing, then the client will maintain it's IP address, and pass traffic in the interface that it joined initially.  The WLC will have the client entry in the MSCB, linking the cleint MAC and IP, as wel as which AP it's currently connected to.

HTH,

Steve

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[janesh_abey]

Hi Steve,

Thanks for the reply.Thats is exactly what i'm talking about.

Based on your reply, it means that the client do not have to refresh the IP although it roamed to a different subnet.

Steve, would you also happen to know what is the mechanism/technology  utilised to achieve this behaviour?

Also if you can point me to a reference that would be very much appreciated.

Thanks,

Janesh

[Stephen Rodriguez · Accepted solution]

Janesh,

     Correct, the client does not need to refresh it's IP, or get a new one. 

     The configuration guide and the mobility FAQ should speak to this.  As for the mechanism.  When you are roaming inside the same WLC it knows that the client hasn't moved off of it, so it just updates the MSCB entry and the client rolls along.

     Now if you roam from WLC-A to WLC-B, the WLC looks at the interface name, and ip address assigned to that interface.  If the subnets match, the MSCB entry from WLC-A is moved to WLC-B.  The traffic for the client will ingress and egress on WLC-B.  This is a Layer 2 roam.

     Now the client roams from WLC-A to WLC-B, the WLC looks at the interface name, and ip address assigned to that interface.  The subnets do not, WLC-A copies the MSCB entry to WLC-B, then they pass the client traffic between them for the client.  The traffic will ingress on WLC-A, be sent accross the mobility tunnel to WLC-B, and then to the client.  The inverse is true for traffic from the client.  It flows from the client to WLC-B, across the mobility tunnel to WLC-A, and then egress to the network there.  This is a Layer 3 roam.

HTH,

Steve

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[George Stefanick]

Steve +5 ... You did a great job explaining mobility roaming ... I even think Leo finally understands it for the first time ! LOL

[iores]

@Stephen Rodriguez 

Is this valid only for central switching? What if local switching is used? Will the client need to go through the whole authentication process again? SSID is the same except AP1 tags traffic in VLAN A, and AP2 tags traffic in VLAN B.

[janesh_abey]

Thanks Steve and Leo.Thats what I was after.

cheers,