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Failover Configuration

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Jan 4th, 2010
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I have two buildings that are connected together by a multimode fiber.  At each building there is a Cisco 1841 router that connects to HQ site via a PTP T1 circuit.  Also at each building there is a Cisco 3750 48 port switch for LAN connectivity.  I would like to configure a failover configuration, so if one router fails in either building, the building with the failed router can route traffic to the other building.  Each building has their own subnet range.

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danrya Mon, 01/04/2010 - 22:26
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You would have to configure routing on the switches and either use static routes with different costs, or a routing protocol like OSPF.  If you configure routing between HQ and the two sites, and then configure it between the two sites, all traffic destined to the HQ would use the local link.  If that link is down, it would traverse the other site.


Is the link between the sites a Layer 2 (switched) link, or routed?


If you post the basic config, I'm sure the community can help you sort out the config that will work.  By basic config I mean are you routing or switching what are the VLAN id's on the 3750's.


Dan

Marwan ALshawi Tue, 01/05/2010 - 00:34
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if the connection between the sites L2 then you can

use HSRP as following:


i will assume the following:

each site use one vlan for  to reach the router in each building

lets say in building 1 you have the switch operating in L2 only ( no routing)

in building 2 you are using vlan 20


make the L2 link between the sites as trunk that pass vlan 10 and 20


- as long as each site uses its own subnet in this case you need to make the link between the switch and the router inside interface as trunk in the switch

and in the router inside interface you need to create two subinterfaces


lets say building 1

vlan 10

network 10.1.1.0/24


building 2

vlan 20

network 20.1.1.0/24


as mentioned above vlan 10 and 20 have to be created in both switches

and trunked between them as well ( i wish the inter sites link is L2)


site 1 router


int fa0/0.1

encapsulation dot1q vlan 10

ip add 10.1.1.1 255.255.255.0

standby 1 ip 10.1.1.100

standby 1 preempt

standby 1 priority 110

standby track int [ousideinterface going to the HQ]


int fa0/0.2

encapsulation dot1q vlan 20

ip add 20.1.1.2 255.255.255.0

standby 2 ip 20.1.1.100

standby 2 preempt

standby 2 priority 100


site 2 router


int fa0/0.1

encapsulation dot1q vlan 10

ip add 10.1.1.2 255.255.255.0

standby 1 ip 10.1.1.100

standby 1 preempt

standby 1 priority 100


int fa0/0.2

encapsulation dot1q vlan 20

ip add 20.1.1.1 255.255.255.0

standby 2 ip 20.1.1.100

standby 2 preempt

standby 2 priority 110

standby 2 track int [ouside interface going to the HQ]


in this case site 1 default gateway will be 10.1.1.100 and the primary exit will be the router in building 1 if this router fail or the link to the HQ goes down the router in building 2 will take over same concept for building 2


this is based on the assumption that the link between the two buildings is L2

if not the above solution is not valid


if link between the buildings is L3 router link in this case you need to consider routing and as mentioned in the previous post you will need to enable routing in the switches to have a redundant path to the HQ

you can use any routing protocol but this depends on what routing you use between each site and the HQ site


good luck

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jdleon Tue, 01/05/2010 - 06:16
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You are correct to assume on the way the two buildings are configured.  I will test your config and let u know how it goes.  Thank you.

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