Router/WAN redundancy and Cat 3750 stackwise

Unanswered Question
Jun 20th, 2007

Hi, can you clarify this.

Please find attached simplified diagram.

My questions are:

a) If both 3750-Switch1 and 3750-Switch2 are configured as stackwise (cable), what should I consider and configure on port fa1/0/20 on both switches Switch1 and Switch2 if I want to connect (2) routers connected to different ISPs to the 3750 switches?

Should I run iBGP in the 3750 switch in order to make it pick Router1-ISP1 as the preferred route and Router2-ISP2 as my lower priority local preference? Is that it?

b) Is that the typical design you would do, or should I plan to connect another interface (fa0/1) of both routers to the other switch, so that could give me additional redundancy. Please let me know if you guys are doing that.

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Edison Ortiz Wed, 06/20/2007 - 08:31

a) iBGP will be a good method for implementing route-preference and filtering.

b) Configuring another interface from the routers will provide full redundancy. If you are able to do it, go for it.

news2010a Wed, 06/20/2007 - 09:25

Here is what I am unsure. Imagine I am doing the configuration on the switch(s) in order to connect both routers:

On Switch-3750-1:

int fa1/0/20

no switchport

ip add

On Switch-3750-2:

int fa1/0/20

no swtichport

ip add mask

Is that how it is supposed to work? I mean, although the switches are configured in a stackwise fashion, is that OK I can setup IP addresses, etc everything different on both switches in the stack?

royalblues Wed, 06/20/2007 - 10:51

Friend there are ways to do it.

If you own your own address space you can just use the stackwise connection and just configure HSRP on the ISP routers and track the wan link to ISP.

BGP can also be used but when you do a stackwise connection the whole unit behaves as one switch and there is no need to confogure IBGP. you can either set weight or local preference for routes received from the ISP routers and make the routing decision.

You can set IP addresses on the ports in the stack just as a normal L3 switch by using the no switchport. The stackwise doesn't change the behavior of the switch but just makes it a single unit connected over a 32 Gbps bus. The command however would change as the interfaces of the 2nd switch would chnage to int fa 2/0/20

HTH, rate if it does


Edison Ortiz Wed, 06/20/2007 - 11:04

You can go L3 between switches and routers as well. That's another posibility.


This Discussion