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Layer 3 switches duplicate address

I'm using packet tracer and I setup  a network with a few layer 2 switches and a layer 3 switch and some hosts in various vlans. Everything is working fine and all hosts can ping each other on every vlan.

I then added a second layer 3 switch (trunked it to the existing layer 3 switch) and gave it an ip address on the management interface (int vlan 100 ip address x.x.x.x), I was then able to ping this switch only from a host on the management vlan but not hosts on other vlans, ok makes sense. I then manually added all the other int vlans on the switch and I am now able to ping this new layer 3 switch from all hosts. I also entered the "ip routing" command and all the vlans came over from vtp. So everthing seems to be working fine.

But, after I added all the int vlans on the new layer 3 switch, I was watching the console on the other layer 3 switch (the former one) show these messages

duplicate address x.x.x.x on vlan 10 sourced by sourced by 0005.5E10.96C2

duplicate address x.x.x.x on vlan 20 sourced by sourced by 0005.5E10.96C2

duplicate address x.x.x.x on vlan 30 sourced by sourced by 0005.5E10.96C2

Everything seems to be fine, but I'm wondering if I did something wrong by added those int vlans on the new layer 3 switch?

Also, with both these layer 3 switches, do I setup on both of them or only one of them the route to the router for all traffic? I have all traffic going to the layer 3 switches and on th elayer 3 switches I dont know if both or just one need to forward everything to the router fo interent access.

Thanks!      

1 REPLY
Hall of Fame Super Blue

Layer 3 switches duplicate address

If you are setting up the same vlans on both switches using L3 vlan interfaces they need to be using different IPs. You generally would use HSRP for those vlans for the end devices eg.

vlan 10 = 192.168.5.0 255.255.255.0

switch 1

======

int vlan 10

ip address 192.168.5.2 255.255.255.0

standby 10 ip 192.168.5.1

standby 10 priority 110

standby 10 preempt

switch 2

=======

int vlan 10

ip address 192.168.5.3 255.255.255.0

standby 10 ip 192.168.5.1

then set the default gateway on your clients to point to the virtual IP of 192.168.5.1. Notice in the above config each interface has a different IP address configured for the physical IP but they share a virtual IP.

Jon

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