Two L3 switches as a redundant / mated pair

[leoruben2308]

Hello, I hope someone can help me out here as I have been thrown a pile of hardware and been instructed to configure a redundant network from scratch, using my puny CCNA certified skills... :/

I have attached a diagram of what this network looks like, I just need to configure it to work!

So There are two Cisco 4900M L3 switches and two Cisco 2960 L2 switches. I need to configure the two L3 switches to operate as a redundant pair, as the servers connecting to them are connecting using bonded interfaces, which can only have one default gateway. So these two L3 switches need to have the same Vlan interface 1, 2 and 3 IP's set onto them.

How is this done? How are the two L3 switches made aware of each other? via a normal trunk? Is there some special configration for configuring a mated/redundant pair of switches? or are they both just configured as though they were the same switch, but linked?

Ive been reading up on VRRP, would this solution work for this?

Any help would be much appreciated, thanks!

[Ton V Engelen]

Hi

i think you need HSRP or VRRP, yes, this should work.

There should be a trunk between the l3 switches, and you ll need to configure each vlan with and ip address and a standby ip adress plus a standby priority.

Also on layer 2 best practise is to make the switch with the highest HSRP priority also make root bridge for that vlan.

I do not have much time right now, but i could sketch a setup example for you tomorrow.

[leoruben2308]

Hi Ton V, thanks alot, looks like VRRP is the answer, not just have to work out how to implement it! An example would be great.

[Reza Sharifi]

VRRP should work fine with a trunk between the switches

Here is sample config you can use:

switch-1

interface Vlan10

ip address 10.10.10.1 255.255.255.0

vrrp 10 ip 10.10.10.3

vrrp 10 priority 120

end

switch-2

interface Vlan10

ip address 10.10.10.2 255.255.255.0

vrrp 10 ip 10.10.10.3

end

in this case switch-1 has a higher priority, so it is the active device

HTH

[leoruben2308]

Hi Reza, thanks for this. So hosts on the network on vlan 10 would be set with the default gateway of 10.10.10.3?

[Ton V Engelen]

Hi, default gateway of 10.10.10.3 yes, that is correct

In this example, switch 1 is VRRP master for vlan 10.

Make sure that the switch 1 will be root of this vlan at layer 2 by setting the spanning tree priority (low)

Make sure switch 2 has a higher priority than switch 1 on l2, but lower than the other switches.

Repeat this for each vlan, and make switch 2 master for the next vlan, then switch 1 master for another  next vlan etc

That way you ll have load share on both links.

[leoruben2308]

Ok I will give this a try. I dont think bandwidth will be an issue as this is all on a 10Gb switching platform, so we dont need to load balance specifically, but I will keep that option in mind incase its required. Currrently I just want to get the redundancy working

[Reza Sharifi]

with few vlans, you don't to worry about load balancing. Keep it  simple with one switch as the active and root and the other stand-by and  backup root for all vlans.

HTH

[leoruben2308]

Another question, I intend to have all the servers on Vlan 1 and Vlan 3 (in the diagram) also connected to each L2 switch via bonded interfaces. Does the same vrrp config get applied to each Vlan interface?

So for example like this? (ive adjusted the vlans to match mine currently setup)

switch-1

interface Vlan1

ip address 10.10.10.1 255.255.255.0

vrrp 10 ip 10.10.10.3

vrrp 10 priority 120

end

interface Vlan2

ip address 10.10.20.1 255.255.255.0

vrrp 10 ip 10.10.20.3

vrrp 10 priority 120

end

interface Vlan3

ip address 10.10.30.1 255.255.255.0

vrrp 10 ip 10.10.30.3

vrrp 10 priority 120

end

switch-2

interface Vlan1

ip address 10.10.10.2 255.255.255.0

vrrp 10 ip 10.10.10.3

end

interface Vlan2

ip address 10.10.20.2 255.255.255.0

vrrp 10 ip 10.10.20.3

end

interface Vlan3

ip address 10.10.30.2 255.255.255.0

vrrp 10 ip 10.10.30.3

end

[ALIAOF_]

Unless you have multiple vendors instead of VRRP I think you should use GLBP.  Both switches will be Active/Active with GLBP.

Setup a port channel between the two core switches using the ten gig ports.

Now on the 2960 diagram shows 10Gig Trunk.  2960's do not have a 10Gig port.

[leoruben2308]

Hi Mohammad, thanks ill have a look at that. Sorry for the confusion thats a mistake on the diagram, they are 1Gb trunks.

[leoruben2308]

Hi Mohammad, after a bit of review, I think you are right it is best that I use GLBP, as the switches will in fact need to be in an active/active state for the bonded interfaces to work. Is the config basically the same as VRRP? Is a port channel between the switches required or will the currently configured trunk between them work?

Could I please ask for a simple example config for this so I can get my head around it? Would be much appreciated!

[ALIAOF_ · Accepted solution]

You can leave the trunk between two core switches but doing a port channel would be better for redundancy purposes. 

With GLBP basically you'll need 3 IP's.  I have mine configured with VLAN's like this:

Switch 1:

interface Vlan200

description MGMT

ip address 10.1.200.249 255.255.252.0

ip helper-address 192.168.0.2

glbp 200 ip 10.1.200.1

glbp 200 priority 110

glbp 200 preempt

glbp 200 weighting 5

glbp 200 load-balancing weighted

glbp 200 authentication md5 key-string 7 ***********

glbp 200 weighting track 200 decrement 20

end

Switch 2:

interface Vlan200

ip address 10.1.200.250 255.255.252.0

ip helper-address 192.168.0.2

glbp 200 ip 10.1.200.1

glbp 200 preempt

glbp 200 weighting 6

glbp 200 load-balancing weighted

glbp 200 authentication md5 key-string 7 ***********

glbp 200 weighting track 200 decrement 20

end

Here are some good links and a really awesome cheat sheet:  I know there is a whole lot of information but trust me it is better to have more information then less , if you implement you also need to know how to troubleshoot it as well.  Depending on your Network configuration you also will need to consider STP behavior.

http://packetlife.net/media/library/3/First_Hop_Redundancy.pdf

http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/HA_campus_DG/hacampusdg.html#wp1108489

http://blog.ine.com/tag/load-balancing/

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6554/ps6600/product_data_sheet0900aecd803a546c.html

http://www.ciscozine.com/2008/11/18/configuring-redundancy-with-glbp/

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a00807d2520.shtml

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ft_glbp.html#wp1027173

http://cisconinja.wordpress.com/category/hsrp-vrrp-and-glbp/

[leoruben2308]

Wow thanks really appreciate that.

I went ahead and tried configuring it before I saw your reply, and got it working, using a very basic GLBP setup. Only tried it with one VLAN so far and it works fine, each cable whiCh connects to a seperate L3 switch, from the bonded pair from a server can be disconnected and the server keeps a connection to the rest of the network and internet just fine, which is the main thing. here is what I used;

Switch 1

interface Vlan2

description VOICE

ip address 10.0.40.248 255.255.255.0

glbp 20 ip 10.0.40.247

glbp 20 priority 120

Switch 2

interface Vlan2

description VOICE

ip address 10.0.40.249 255.255.255.0

glbp 20 ip 10.0.40.247

You seem to have a much more elaborate config, im just glad its working for now but do you see anything wrong/potential problems with the way I set it ? I will read you links and probably find out for myself soon anyway

[ALIAOF_]

With fewer settings lot of stuff is default so in your case load balancing method is round robin, you might want to add the preempt command so the gateway can take over as AVG if the priority changes.