Bonding router interfaces to different switches

Unanswered Question
May 11th, 2010

I was wondering if anyone out there had a good configuration to connect two interface between two independant switches like 2960 L2 switches and make it HA?  I know your typical bonding won't work because of them not sharing CAM tables but is there a different way?  I also know with a 3750 L3 switch I could do L3 point to point links and route it.

I have this problem too.
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Reza Sharifi Tue, 05/11/2010 - 15:22

Hi,

On small form factor switches, you can only do 802.3ad with the 3750s series if they are stacked.  If you are using other switches ie 3560 or 2960, both links have to be on the same switch.

HTH

Reza

rraver Wed, 05/12/2010 - 19:54

Reza,

So you are saying that there is no way to create two interfaces and make them redudant if they go to seperate switches, even if it's not a bonded configuration?  I was reading an article about using a redudant interface command with the other interface being configured the same, do you know anything about this?

Rob

Ganesh Hariharan Tue, 05/11/2010 - 23:29
I was wondering if anyone out there had a good configuration to connect
two interface between two independant switches like 2960 L2 switches
and make it HA?  I know your typical bonding won't work because of them
not sharing CAM tables but is there a different way?  I also know with
a 3750 L3 switch I could do L3 point to point links and route it.

Can you share a diagramtic view about your query !!

Ganesh.H

rraver Wed, 05/12/2010 - 19:57

Ganesh,

I will do a quick one in ASCII below,

   ------Gig 0/0----| Cisco 2851 |------ Gig 0/1-----

   |                                                              |

   |                                                              |

   |                                                              |

   |                                                              |

|Cisco 2960|----------Port Channe|-------------|Cisco 2960|

The objective is to more or less bond the two interfaces or put them in a mode where they can share the same IP and if one goes down the other will pick up at a layer 2 level.  This rules out any VIP type solution and since their two independant switches it also rules out any true bonding like 802.3ad or port channel solutions.

Reza Sharifi Wed, 05/12/2010 - 20:03

Rob,

It will not work using 2 different 2960 switches.  You can only do this with 3750s if you stack them or use 2 ports from the same switch.  Cross chassis etherchannel is not supported on 2960s

HTH

Reza

Ganesh Hariharan Wed, 05/12/2010 - 22:48

Ganesh,

I will do a quick one in ASCII below,

   ------Gig 0/0----| Cisco 2851 |------ Gig 0/1-----

   |                                                              |

   |                                                              |

   |                                                              |

   |                                                              |

|Cisco 2960|----------Port Channe|-------------|Cisco 2960|

The objective is to more or less bond the two interfaces or put them in a mode where they can share the same IP and if one goes down the other will pick up at a layer 2 level.  This rules out any VIP type solution and since their two independant switches it also rules out any true bonding like 802.3ad or port channel solutions.

Hi,

The only way to link two (or more) switches together in a single Etherchannel is in a stack configuration, this applies to 3750 with cross stack etherchannel and 6500 with VSS.

Nortel appears to have a feature called Split MultiLink Trunking, which does multichassis trunking, you might want to have a look at the document below:

Layer 2 Trunking Availability Strategies using SMLT and DMLT

http://www.informit.com/articles/article.asp?p=169544&seqNum=3&rl=1

Hope to Help !!

Ganesh.H

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skleinart Wed, 01/05/2011 - 02:05

I was just looking into the same thing, I haven't yet lab'd it or tested anything, but plan to tomorrow....  here's what I came across:

(copied from http://searchnetworking.techtarget.com/tip/Router-Expert-Implementing-router-interface-redundancy )

The backup interface command "bonds" two interfaces on the router to behave as one. One is the primary, the other secondary. When the router detects a link failure on the primary, the secondary becomes active and remains active until the primary is restored. The backup interface command is defined on the primary interface:


Router (config)#int fa 0/0
Router (config-if)#backup interface Fast Ethernet 1/0


Both the primary interface and its backup should be configured identically. The primary interface dictates the operation state of the bond. If the primary interface is shut down, the backup is as well. Another little caveat of using interface backup is that the primary interface's slot and/or number must be lower then the backup interface. Otherwise, when the router reboots, the backup interface comes up first at boot. The router detects the IP address duplication and wipes out the IP address configuration of the primary. When the router is up and running, you should check the operation status of the bond using the command:


Router#show backup
Primary Interface Secondary Interface Status
--------------------- ----------------------- -------

FastEthernet0/0 FastEthernet2/0 Normal
FastEthernet1/0 FastEthernet2/1 backup mode

---

I know this is exactly what I am looking for in my lab environment... hopefully it works as planned.

j-marenda Wed, 01/05/2011 - 09:17

You may want to put the two interfaces of your router into a bridge group,

configure your ip on that bridge group, run stp on the router for this bridge.

CON: Router will run per-vlan spanning-tree (not :rapid)

         and limit MTU to 1500 .

So you may prefer to the backup interface thing.

Or better: use TWO routers and HSRPv2 .

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