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Cisco IOS Configure Transit with HSRP


wildweaselmi
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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 10.63.32.240/28



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:



10.63.32.241 - HSRP address for Layer3 Switch



10.63.32.242 - Layer3 Switch1



10.63.32.243 - Layer3 Switch2



----



10.63.32.252 - Router2



10.63.32.253 - Router1



10.63.32.254 - 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 10.63.32.242 255.255.255.224


sw1-3750(config-if)# standby 1 ip 10.63.32.241


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


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


----


sw2-3750(config-if)# ip address 10.63.32.243 255.255.255.224


sw2-3750(config-if)# standby 1 ip 10.63.32.241


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 0.0.0.0 0.0.0.0 10.63.32.254

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 0.0.0.0 0.0.0.0 10.63.32.254

Sw2-3750(config)# no ip http server


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

![/code]



Note: The command ip default-gateway 10.63.32.254 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 0.0.0.0 0.0.0.0 10.63.32.254


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