Re: Adding 3rd L3 Switch As Trunk

BashedRoot · ‎09-26-2017

I have a couple of 24-port Cisco switches (L3) that I use for my servers. I'm running out of ports at this point and have fully utilized TCAM of 24k per switch (I route a large number of IPv4 for VPN services).

WS-C3650-24TS

How would I easily add a third switch as trunk? I do not stack due to Cisco's method of having one 24k utilization per stack instead of per switch, hence why I trunk them instead.

I'd appreciate if someone explains in laymen terms how to add this as a trunk. Current #2 switch is set up as trunk. I'll probably have it in the same cab as the second switch for now.

Thank you in advance

Reza Sharifi · ‎09-26-2017

Are the default gateways (SVls) for all the vlans located on the existing 2 switches?

Are you running HSRP or VRRP?

If you want to add a 3rd switch and have it be the default gateway for all your vlans, you may need to run GLBP. Have a look at this link for config examples:

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3650/software/release/3e/ip/configuration_guide/b_ip_fhrp_3e_3650_cg/b_fhrp_3se_3650_cg_chapter_01.html

HTH

BashedRoot · ‎09-27-2017

> Are you running HSRP or VRRP?

Can you please explain how I check this? I had to let the network guy go due to conflicts but I've learned a lot, however not fully at network engineer status. However, if you give me the commands to run I can certainly get you the info.

This is my current setup

Switch #1 (Primary L3)

Gateway: .52

Switch #2 (Trunked as L2)

Gateway: .53

Hardware (Dell servers) are assigned as:

1 VLAN per server / per switchport. VLANs per server are created solely on the swithports they're plugged into, not each switch.

Note: Due to TCAM utilization and trunk setup, IPs are pulled in from upstream on Switch #1. Any IPs assigned on switch #2 per VLAN are forwarded from switch #1 to switch #2 like this:

ip route xxx.xxx.98.24 255.255.255.248 xxx.xxx.xxx.53

So the .53 is the switch #2 gateway. This method allows L3 networking on each switch per VLAN and fully utilize TCAM, 24k per switch.

So, now I want to add a third L3 switch using gateway .54 and create VLANs there for servers ported there, just as I'm doing currently. Simple thing I want to do. My question is, how do I add this new switch as another trunk? What's the configuration process?

Richard Burts · ‎09-27-2017

If we knew more about your environment we might be able to provide better suggestions. But based on the little that I know so far, here are my suggestions:

- choose a port on switch 2 and a port on switch 3 that will be used to connect the switches.

- configure both ports as trunks (the most important thing is switchport mode trunk, other paramters are possible - use the existing trunk port connecting switch 2 to switch 1 as a model to follow).

- connect the ports between switch 2 and switch 3.

- configuration of switch 3 (gateway, vlans, routing, etc) can follow the process that you used on switch 2.

HTH

Rick

HTH

Rick

BashedRoot · ‎10-16-2017

@Richard Burts wrote:

If we knew more about your environment we might be able to provide better suggestions. But based on the little that I know so far, here are my suggestions:

- choose a port on switch 2 and a port on switch 3 that will be used to connect the switches.

- configure both ports as trunks (the most important thing is switchport mode trunk, other paramters are possible - use the existing trunk port connecting switch 2 to switch 1 as a model to follow).

- connect the ports between switch 2 and switch 3.

- configuration of switch 3 (gateway, vlans, routing, etc) can follow the process that you used on switch 2.

HTH

Rick

Hi Rick,

Thanks for that tip. Could I trouble you to please provide step by step commands to run to accomplish this? It's been a long while so I'd rather play safe here. The new gateway IP for the 3rd switch (for example) will be xxx.xxx.xxx.54. Thank you.

Philip D'Ath · ‎09-26-2017

Go into interface configuration mode for the port linking to the other switch and go:
macro apply cisco-switch

Repeat on the other switch.

BashedRoot · ‎10-16-2017

@Philip D'Ath wrote:
Go into interface configuration mode for the port linking to the other switch and go:
macro apply cisco-switch

Repeat on the other switch.

Hi Philip,

Could you please explain what exactly this does?

Asemmoqbel · ‎10-16-2017

Hi,

To better help you and provide you good solution. Could you explain more about your setup and how you want the traffic to flow between the switches especially about the gateway in the third switch and if you could post a diagram will be best.