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Kyle Brandt
Asked: 2010-02-03 11:53:39 +0800 CST

Redundant links from Router to Switches

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With a setup of two NICs on a server into two different switches where each NIC has a different IP (But both on the same network), and then the switches to the router. How would I configure the two ports on the router to be redundant so that one port goes to one switch and the other port to the other switch. The router is a Cisco 3825, switches are Dell Power connect 5324s.

The idea being that as long as applications on the server are configured to work with both IPs, any 1 NIC or 1 switch could fail and the service would still be up. I understand the router would still be a single point of failure.

Update:
Little background, I moving my whole datacenter and don't have that much time to plan, so this sort of redundancy might be out of the scope of what I can learn and do with the time I have.

However, I am going to be rewiring everything and maybe purchasing stuff. I almost have enough switches to connect all servers to two different switches, and have a 3800 and a spare 2800 router. If I keep configurations as they are now, but put the second NIC into a redundant switch for each server, and then those second switches into the second router, will I be ready to set up this sort of redundancy as far as physical configuration is concerned? Might this configuration be limiting in my redundancy options, or which route I go will this basically be the physical layout?

networking cisco redundancy dell-powerconnect

3 Answers

  1. Best Answer

    You are going to have to setup dot1q trunking between the switches and the router (BTW did you mean 3825?) and then create a vlan interface on the router. You will not be able to have two router interfaces within the same IP address subnet otherwise.

    You may need a switching module in the router for this to function as desired -- such as the NME-16ES-1G.

    [edit / additional information]

    You will not be able to have two router interfaces in the same subnet unless you either: (a) use a BVI interface as Vatine suggested (there are performance and other considerations using them however) or (b) put the two physical interfaces into a vlan (see example below).

    !
interface FastEthernet0/3/0
 switchport access vlan 10
 switchport mode access
!
interface FastEthernet0/3/1
 switchport access vlan 10
 switchport mode access
!
interface FastEthernet0/3/2
 switchport mode access
 shutdown
!
interface FastEthernet0/3/3
 switchport mode access
 shutdown
!
interface Vlan10
 description Server_Vlan
 ip address 192.168.10.1 255.255.255.0
!

    If you have two routers, then you could provide IP address/gateway redundancy for the servers by using HSRP, VRRP or GLBP.

    [edit / additional information (HSRP example)]

    interface Vlan10
 description Server_Vlan
 ip address 192.168.10.2 255.255.255.0
 standby ip 192.168.10.1
 standby priority 150
 standby preempt
!

    For your second router, change Vlan10 to ip address 192.168.10.3 and a priority of 140. Use the command "show standby brief" on both routers to confirm HSRP operation.

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  2. Why not setup NIC teaming or bridging on the NICs on the server so that both NICs on the server share a single IP.

    You shouldn't need to do anything special to the ports to make sure this works. As long as the switches aren't cross connected to each other you shouldn't even need spanning tree turned on.

    • 1

  3. One way would be to configure a bridge-group on the router and set a single default gateway as the IP address of the resulting BVI interface.

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