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Connecting L3 switches

Posted on 2013-12-26
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Last Modified: 2013-12-26
I have a network with L2 switches and a L3 switch connected directly to the ISP router. If I want to add another L3 switch though how would I set it up? Since the current L3 switch is doing the vlan routing and routing all the traffic to the router for internet access, what role does the second L3 play?

1. Will the vlan interfaces I created on the current L3 switch come over by its self, vtp possibly, or do I have to manually recreate them? Is it even possible to create the interface vlan xx's since they may even have ip conflicts?

2. If it is possible to add this switch, then which L3 switch will do the routing for the vlans, both? Which will be the L3 that routes to the ISP router? Does one of them have to be setup as a downstream L3 switch?

This and any other information that i need to know on how to add this switch please let me know.
Thanks.
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Question by:tolinrome
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by:Miftaul
Miftaul earned 250 total points
ID: 39740310
1. Do you really need the vlan interfaces on the new L3. Only management SVI should be fine. Its always secured to manually create the VLAN than using VTP. But its possible to Configure IP for SVIs, you just have to assign different IPs on the same subnet.

2. You can add the new L3 next to each other and configure first hop redundacy eg VRRP. Both switchcan do routing for selective VLANs but can failover for the other.
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by:tolinrome
ID: 39740324
ok, so then I dont need to create the vlan interfaces on the new L3. But now that I think about it, since all the vlans default gateways are the ip's on the vlan interface on the L3 switch, if I add the second L3 switch what sense does it make then to add the new vlan interfaces, it would be duplicate ip addresses the vlans would then have 2 separate default gateways, no?

What purpose then really would I want to install another L3 switch? What would impel me to do it?
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giltjr earned 250 total points
ID: 39740716
If you want an 2nd L3 switch to take over if the current one fails, you will need to make sure your ISP's routers have a second interface.

You would connect both L2 switches to each L3 switch.
Connect both of your ISP's routers to each L3 switch.

Each L3 switch would need to have ALL vlan's defined on them.

As Miftaul stated, you then setup the L3 switches to use VRRP, or if they are Cisco devices HSRP, on each VLAN.

This way if either of the L3 switches fail, the other one takes over transparently.
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