ArubaOS and Controllers

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Frequent Contributor II

Advantages to VRRP in a Master/Local Setup?

Hello all,

I have two controllers. 1 master and 1 local. Currently my only redundancy is based on the LMS IP and the Back UP LMS IP.
LMS = Local Controller
Back UP LMS = Master Controller
I have not enabled LMS Pre-emption

I wonder if there is any advantage to using VRRP between the master and local controller over this method. As I understand it when an AP can't find its LMS it reboots and then switches to the Backup LMS. Using VRRP and a virtual LMS IP address would prevent this reboot.

So is there any other advantage to VRRP?
If I don’t implement VRRP, is it possible to adjust the time an AP will wait before switching to the Backup LMS? I have a site with a bit of a latency problem and if I was able to adjust this setting it would be helpful.

Cheers.
Guru Elite

No real difference


Hello all,

I have two controllers. 1 master and 1 local. Currently my only redundancy is based on the LMS IP and the Back UP LMS IP.
LMS = Local Controller
Back UP LMS = Master Controller
I have not enabled LMS Pre-emption

I wonder if there is any advantage to using VRRP between the master and local controller over this method. As I understand it when an AP can't find its LMS it reboots and then switches to the Backup LMS. Using VRRP and a virtual LMS IP address would prevent this reboot.

So is there any other advantage to VRRP?
If I don’t implement VRRP, is it possible to adjust the time an AP will wait before switching to the Backup LMS? I have a site with a bit of a latency problem and if I was able to adjust this setting it would be helpful.

Cheers.




Tpelley,

There is no substantial difference in time. When the AP misses "bootstrap threshold" number of heartbeats (8 by default) it will rebootstrap, which means it will attempt to reinitiate a connection with either its LMS then its backup LMS. This normally takes10 to 20 seconds. in either case.


Colin Joseph
Aruba Customer Engineering

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Aruba Employee

Re: Advantages to VRRP in a Master/Local Setup?

Colin, it is possible to avoid reboot if we use VRRP because in VRRP, in either case the LMS ip is the same logical ip of the VRRP group.. True?
MVP

Re: Advantages to VRRP in a Master/Local Setup?

Tpelley,

The AP is not rebooting, it is "rebootstrapping", as Aruba calls it. It'll tear down the GRE tunnel between it and the controller and will create a new one. This is of course disruptive to clients.

I would use VRRP over backup-lms, as from the APs perspective, the LMS IP address is always the same. The controllers handle the VRRP negotiation of who will process the traffic and who will remain silent. This is preferred, as the VRRP "switchover" is within seconds. Backup-lms, as Colin says, must wait until the bootstrap threshold is exceeded before re-establishing the GRE tunnel.

The only reason I foresee backup-lms to be preferred is if the controllers cannot be on the same layer 2 segment, a requirement for VRRP.
==========
Ryan Holland, ACDX #1 ACMX #1
The Ohio State University
Frequent Contributor I

my experience

Might want to look into doing both... with VRRP failover should be quick
But in my case of VRRP between redundant masters I've had the unfortuneate luck of having cases where the master controller gets in a weird state - unable to maintain tunnels to the AP's - but not failed enough to cause VRRP to switch...

Thinking now that perhaps having the backup LMS point to the real backup controller would help in this case specifically where the AP's notice an issue - but the controllers don't think anything is wrong...

of course in the case of master-master redundancy the backup is still standby until it realizes the master is gone so it won't terminate any ap tunnels (that's what I get for running though experiments mid post)
though this might not be an issue for master-local vrrp setups?
Aruba Employee

Re: Advantages to VRRP in a Master/Local Setup?

I would personally choose to skip VRRP in this case only because it's not scalable. You may only have one master and one local at this point (and they're on the same vlan), but if you put another local out at a remote site, VRRP isn't going to come into play and you'll have to use backup LMS.
Aruba Employee

Re: Advantages to VRRP in a Master/Local Setup?

There is good information in the VRD for campus deployments on this topic. VRRP is the preferred method when two controllers are on the same L2 segment, with LMS/backup LMS if they are not. You can find the VRD here:
http://www.arubanetworks.com/pdf/technology/DG_Campus_Wireless_Validated_Reference.zip

-awl
Andy Logan, ACDX
Director, Strategic Account Solutions
Aruba Networks
Contributor II

VRRP is the best choice unless you're L2 challenged in your environment.

You CAN scale VRRP to up to 254 different failback scenarios in each VRRP ID.

We do this in mult-vendor networks for both Wired and Wireless Gateway protection.

(You can have a controller set to priority 254, one to 253, one to 252, .... for tiered failback.)

VRPP also allows some creative control over AP's and failback.

If I have 200 AP's on a controller and a backup controller that only supports 64, I can put 64 in an AP group with a VRRP address as their LMS IP. I put the physical address of the 1st controller in the group supporting the other 136 and if the first controller fails I can control which of my 200 AP's continue to provide services. Since VRRP can have the prioirity changed dynamically as well as be enabled/disabled on a per VRID basis, the administrator has control over where AP's live.

If you feel you have a problematic controller, simply adjust the VRRP priorities for a VRID to move them to the 2nd or 3rd tier unit. (moving to the third tier unit would of course require adjusting the priority on both the first and second or the first and third units to make the third higher than the 1st or 2nd.)
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