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New Member

VLAN routing help requested.


I recently discovered my company has a single cisco 3550 switch which apparently does the VLAN routing. I need to move that switch without interrupting the flow of traffic. I have two possible solutions and wanted to check with the experts before deciding. I was simply going to power down the switch and move it. But I am afraid it might not come back up (and we have no spare). Also, if possible, I'd like to have as little (or none) downtime as possible.

Solution 1 is to purchase another 3550 and configure it identically to the current 3550 and swap the cable connecting it to the other switches.

Solution 2 is to take the spare 2960, upgrade the software to 12.22_55 and attempt to get vlan routing running on it.

Solution 1 gives us the benefit of having 2 switches where we currently only have 1.

Solution 2 removes the single 3550 switch (all other switches are 2960's).

My question is, can I have 2 switches performing vlan routing at the same time? That would make the transition easier.

My 2nd question is, how long would this switch take to boot back up, assuming it came back up?

Appreciate the help.

New Member

Hello Sharkerty,

Hello Sharkerty,

It is very important you have a device backup. Vlan routing needs a router L3 or Sw L3 like your 3550. It would be interesting you purchase a router L3 (e.g. 1800, 1900, depending on your infra) and two switches 2960 depending on the number of workstation, printers, etc.

Question 1 - You need a router to do Vlan routing.

Question 2 - It depends how much config you have on it, but it is around 5 minutes.

Best Regards! 


1. Can I have 2 switches

1. Can I have 2 switches performing vlan routing at the same time? That would make the transition easier.
-Technically, yes by using HSRP or VRRP AND if you distribute whoever is the active L3 HSRP/VRRP interface, e.g., if you have 20 L3 VLANs, 10 will be handled by SW1 and 10 will be handled by SW2

But configuring it in your network will still require downtime since current the gateway IP of your network is in your existing L3 switch device

To give you an analogy:
Current SW:              -Gateway of current network

If you want to implement HSRP or VRRP, you need to change that
Current SW:
New Switch:
Virtual IP:              -Gateway IP

Transistioning into HSRP/VRRP will cause downtime since you need to 'transfer' the IP as the Virtual IP

BUT the good thing about this is, the transition can be  done per L3 VLAN, hence the L3 that you are current configuring will be the only one to go down, but still it will take time to configure 

PS: Check if your switch license supports HSRP

2. My 2nd question is, how long would this switch take to boot back up, assuming it came back up?
-Dude, you have the a spare switch in your hand w/c is the same model, use that to check the boot-up time. Though, probably 5 minutes. BUT allocate a longer downtime/maintenance window of course, at least 1 hour, just in case 


HSRP and VRRP is good idea

HSRP and VRRP is good idea for this.

I am not sure,
but I think that if he use VRRP he will not have downtime because VRRP can use virtual IP address same as physical on interface.

In addition if he use virtual IP address same as on physical interface then this switch will be master for VRRP. So traffic should go through same switch as now.


Hi Milos, you are right, VRRP

Hi Milos, you are right, VRRP can use the physical interface IP, but if we do that, the current switch will still be the master since making the VIP=interface IP will make whoever the owner of the interface IP to always be the master, note we want to share the load of the L3 details e..g, ARP

Add to that the requirement that is must always be the master when its active, and preempt enabled, soo we are not quite flexible on how we want our switches to behave.

But yeah, if he wants minimal downtime, you can do that OP ^_^ 
It's all up to you OP, but again, check your license :P 

PS: Thanks Milos, I missed that part on VRRP :D 

New Member

1. Create VLANs on the router

1. Create VLANs on the router

2. Assign IP addresses to the each VLAN on the router.

3. Configure the router port connected to the switch as a VLAN trunk port.

4. Define routes to each network.

5. Configure the router to relay DHCP requests.

6. Create the VLANs on the switch.

7. Configure the switch port connected to the router as a VLAN trunk.

8. Add switch access ports to the appropriate VLANs.

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