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Cisco IOS Configure Transit with HSRP


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Instead of having the Routers do all the routing, have your layer 3 switch do it for you. This becomes an advantage when the Router belongs to a third party like ATT, MCI, Sprint, etc.. which makes troubleshooting routing issues difficult due to the lack of access they'll provide.

Here is an example of implementing a transit VLAN (the VLAN that the third party routers and the layer 3 switches reside). In this example there are two layer 3 switches and two third party routers so we will utilize HSRP (which is the desired method for redundancy purposes).

Subnet assigned to the Transit VLAN is

I am going to assign the first three addresses to the layer 3 switch and the last three addresses to the third party routers. So like this: - HSRP address for Layer3 Switch - Layer3 Switch1 - Layer3 Switch2

---- - Router2 - Router1 - HSRP address for two Routers

To configure the two switches we need to add the following commands to the VLAN interface to make the above work.

sw1-3750(config-if)# ip address

sw1-3750(config-if)# standby 1 ip

sw1-3750(config-if)# standby 1 priority 120

sw1-3750(config-if)# standby 1 preempt delay minimum 30


sw2-3750(config-if)# ip address

sw2-3750(config-if)# standby 1 ip

sw2-3750(config-if)# standby 1 priority 90

sw2-3750(config-if)# standby 1 preempt delay minimum 30

also need to update the routing

Sw1-3750(config)# ip route

Sw1-3750(config)# no ip http server

Sw1-3750(config)# ip classless

sw1-3750(config)# ip routing (this command makes a switch layer 3)




Sw2-3750(config)# ip classless

Sw2-3750(config)# ip route

Sw2-3750(config)# no ip http server

sw2-3750(config)# ip routing (this command makes a switch layer 3)


Note: The command ip default-gateway would be used if layer 3 routing wasn't being used but since it is in this scenario the route is covered by the ip route

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