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Community Member

HSRP or GLBP

Hi,

Need an opinion. This is the setup:

Two sites (200 meters apart) with a router installed in each site. Each router as it's own WAN link belonging to the same network.

Each site has a 3550 which is connected to the router. Between the 3550, there's a fibre link connecting each other for redudancy purpose.

If the fibre breaks, i want both sites to be functional. Which setup would be the preferred choice : HSRP or GLBP.

Thanks

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Silver

Re: HSRP or GLBP

Hello Tony,

unfortunately in that case of fiber broken between the two switches you have 50% probability that return packet will go to the right side:

some hosts can be lucky and see their return traffic, but others will be able to send traffic but not to receive it

from the core point of view both WAN links are good to reach hosts in the client Vlan IP subnets it is impossible to say what host is reachable via R1 and what are behind R2.

However, you can double the fiber link or even use three different links between switches (with or without using an etherchannel) in order to reduce the probabilities of this scenario.

Hope to help

Giuseppe

7 REPLIES
Hall of Fame Super Blue

Re: HSRP or GLBP

Tony

If i understand correctly then if the fibre breaks both sites would go active with both HSRP and GLBP.

What determines which one you use is under normal conditions do you want only one sites WAN connection to be used (HSRP) or would you rather use both (GLBP).

Jon

Community Member

Re: HSRP or GLBP

Jon,

I prefer HSRP, one active site at a time. My concern, if link breaks, do both WAN links become active ? also do both sites stay functional ?

Tony

Hall of Fame Super Blue

Re: HSRP or GLBP

Tony

If the fibre link breaks then both sites will think they are the active router and will answer queries for the HSRP VIP. So from an HSRP respect yes i think it would work.

One thing i didn't ask - is HSRP running on the 3550 switches or the routers ?

Jon

Hall of Fame Super Silver

Re: HSRP or GLBP

Hello Tony,

unfortunately in that case of fiber broken between the two switches you have 50% probability that return packet will go to the right side:

some hosts can be lucky and see their return traffic, but others will be able to send traffic but not to receive it

from the core point of view both WAN links are good to reach hosts in the client Vlan IP subnets it is impossible to say what host is reachable via R1 and what are behind R2.

However, you can double the fiber link or even use three different links between switches (with or without using an etherchannel) in order to reduce the probabilities of this scenario.

Hope to help

Giuseppe

Hall of Fame Super Blue

Re: HSRP or GLBP

Giuseppe

Very good point. I was assuming for some reason that Nat was being done on the WAN routers but i have no idea why i assumed that.

Good catch.

Jon

Blue

Re: HSRP or GLBP

Jon, I liked your answers. I figured Id rate ya.

Community Member

Re: HSRP or GLBP

Giuseppe,

Your explantion makes sense. Thanks for your help. You too Jon.

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