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Contributor I
Posts: 65
Registered: ‎12-15-2011

Problems with L2 Failover and L3 Forwarding to Uplink Router

[ Edited ]

I have N+1 sparing for resiliency using LMS and backup LMS IP. That is I have N local controllers and 1 backup controller. All the controllers are on a switch so that all the user VLANs go to all the controllers. I am also routing from the controller to the uplink router - that is the controller has all the users gateway addresses.

 

Now, when a controller fails, its traffic goes to the backup LMS. Since the VLANs are already there, all the sessions can continue with a very short interruption - in theory. But here is the problem. The uplink router has a route back to the controller for each user vlan. When the controller fails, traffic goes to the backup controller but the uplink gateway still has a route to the failed controller. How can I fix this while maintaining the L3 forwarding to the uplink router?  Perhaps OSPF with link priority/weight is the answer.  When a controller fails, OSFP will update the routes at the uplink router.

 

Thanks

Guru Elite
Posts: 21,480
Registered: ‎03-29-2007

Re: Problems with L2 Failover and L3 Forwarding to Uplink Router


MortKaye wrote:

I have N+1 sparing for resiliency using LMS and backup LMS IP. That is I have N local controllers and 1 backup controller. All the controllers are on a switch so that all the user VLANs go to all the controllers. I am also routing from the controller to the uplink router - that is the controller has all the users gateway addresses.

 

Now, when a controller fails, its traffic goes to the backup LMS. Since the VLANs are already there, all the sessions can continue with a very short interruption - in theory. But here is the problem. The uplink router has a route back to the controller for each user vlan. When the controller fails, traffic goes to the backup controller but the uplink gateway still has a route to the failed controller. How can I fix this while maintaining the L3 forwarding to the uplink router?  Perhaps OSPF with link priority/weight is the answer.  When a controller fails, OSFP will update the routes at the uplink router.

 

Thanks




 

Make the Router the Layer3 for all clients.  Make the controller ONLY layer2 for the client VLANs.

 

That is the best   easiest way to do that.

 

You can try running OSPF on the controllers and have it update the upstream router, but that can be complicated and is not straightforward.

 



Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

Contributor I
Posts: 65
Registered: ‎12-15-2011

Re: Problems with L2 Failover and L3 Forwarding to Uplink Router

 I believe my controllers are L2 (ie gateway) for the users and the uplink router is L3 (ie next hop).  The router has static routes back the controllers for each VLAN/subnet.  I need help to understand your answer.

 

Thank-you.

Guru Elite
Posts: 21,480
Registered: ‎03-29-2007

Re: Problems with L2 Failover and L3 Forwarding to Uplink Router


MortKaye wrote:

 I believe my controllers are L2 (ie gateway) for the users and the uplink router is L3 (ie next hop).  The router has static routes back the controllers for each VLAN/subnet.  I need help to understand your answer.

 

Thank-you.


The controllers need to share the same layer 2 VLAN to put clients on the same subnets, otherwise you will have the issue you described.  Let me say this, and I hope it makes sense:

 

Controller 1 - Client VLAN 3

Controller 2 - Client VLAN 3

Controller 3 - Client VLAN 3

 

Router A that they are connected to, is the default gateway for client VLAN3 and the ip interface on the router for VLAN3 has a helper address that points to a DHCP server that will give out the same address to a client, no matter what controller he is on, because his traffic is always being bridged to VLAN 3 on router A.

 



Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

Contributor I
Posts: 65
Registered: ‎12-15-2011

Re: Problems with L2 Failover and L3 Forwarding to Uplink Router

[ Edited ]

I think I understand.  I was trying to avoid making the router the default gateway for the vlans because, of MAC table size issues.  I have a lot of controllers (and clients) using the same uplink router which causes problems with MAC table size.  That is why I needed the controllers to be the default gateway and then route to the uplink router.  Perhaps I am still missing something.   Thanks.

Guru Elite
Posts: 21,480
Registered: ‎03-29-2007

Re: Problems with L2 Failover and L3 Forwarding to Uplink Router


MortKaye wrote:

I think I understand.  I was trying to avoid making the router the default gateway for the vlans because, of MAC table size issues.  I have a lot of controllers (and clients) using the same uplink router which causes problems with MAC table size.  That is why I needed the controllers to be the default gateway and then route to the uplink router.  Perhaps I am still missing something.   Thanks.



The majority of high redundancy deployments are done this way.  I have not personally observed anyone with mac table size issues in their router.  Is this a particular model that has this particular issue?



Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

Contributor I
Posts: 65
Registered: ‎12-15-2011

Re: Problems with L2 Failover and L3 Forwarding to Uplink Router

[ Edited ]

Without getting too specific, I may have more client associations then there are supported MAC addresses because it is a large deployment. However,  if this is the recommended approach, then perhaps I need to reconsider my scaling.

 

Thank-you.

Contributor I
Posts: 65
Registered: ‎12-15-2011

Re: Problems with L2 Failover and L3 Forwarding to Uplink Router

To cjoseph,

Further to the solution of extending vlans to the uplink router, can you please tell me what router redundancy method is used?  If I extend 100 VLANs to the router, VRRP on the router gets very complicated. 

 

Thanks.

Guru Elite
Posts: 21,480
Registered: ‎03-29-2007

Re: Problems with L2 Failover and L3 Forwarding to Uplink Router


MortKaye wrote:

To cjoseph,

Further to the solution of extending vlans to the uplink router, can you please tell me what router redundancy method is used?  If I extend 100 VLANs to the router, VRRP on the router gets very complicated. 

 

Thanks.


I have never seen a deployment with 100 VLANs so I assume that you are just joking.  If your controller is only connected to a single router, there is no redundancy, because that is your only path out.  If there are two routers, you would create a VRRP or HSRP (Cisco) between those routers on that client VLAN and the client's default gateway would be that VRRP or HSRP instance.

 

When controller A fails, the AP fails over to controller B and traffic is bridged to the same VLAN, the default router in the ARP table is the same, the DHCP server is the same (external), etc.

 



Colin Joseph
Aruba Customer Engineering

Looking for an Answer? Search the Community Knowledge Base Here: Community Knowledge Base

Contributor I
Posts: 65
Registered: ‎12-15-2011

Re: Problems with L2 Failover and L3 Forwarding to Uplink Router

The 100 number is the sum of the VLANs over all the controllers, not per controller.

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