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Beginner

GLBP and Loop-Free Topologies

I was reading material for my ENCOR studies, and I came across this section:

 

"Gateway Load Balancing Protocol
(GLBP) provides greater uplink utilization for access layer-to-distribution layer
traffic by load balancing the load from hosts across multiple uplinks; the
downside is that it works only on loop-free topologies."

 

Why doesn't GLBP work with loop-free topologies? Does this mean that GLBP can't be implemented in a topology where STP has blocked links? I have searched Google, and I haven't found any information. Perhaps I haven't been asking the right question.

 

Any input is appreciated. I will mark solutions where they're due.

 

*Edit: I made an error with my question. I meant to ask "Why doesn't GLBP work with looped topologies (i.e w/o STP)

 

 

Everyone's tags (7)
2 ACCEPTED SOLUTIONS

Accepted Solutions
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VIP Mentor

Re: GLBP and Loop-Free Topologies

Hello
Loop free would mean the first hop protocol such (GLBP/HSRP/VRRP) isn't running on a L2 extended vlan topology - vlans that dont extend across multiple access layer switches and the distribution /core layer interconnects are routed (L3) and not trunked (L2)) so then any failure on an upstream link towards the FHRP vip doesn't need rely on stp to convergence to the correct path as the primary active FHRP node.

However when this topology cannot be applied especially with GLBP its suggested that stp disables the the correct l2 interconnect port in times of convergence in a deterministic manner so not to make a sub-optimal L2 switching path for the access-layer hosts towards each GLBP AVF.



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future

View solution in original post

Highlighted
VIP Mentor

Re: GLBP and Loop-Free Topologies

Hello

Please review this link has have managed to find, It discuses relatively what i have explained here but in a much clearer way for you to understand  - here



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future

View solution in original post

3 REPLIES 3
Highlighted
VIP Mentor

Re: GLBP and Loop-Free Topologies

Hello
Loop free would mean the first hop protocol such (GLBP/HSRP/VRRP) isn't running on a L2 extended vlan topology - vlans that dont extend across multiple access layer switches and the distribution /core layer interconnects are routed (L3) and not trunked (L2)) so then any failure on an upstream link towards the FHRP vip doesn't need rely on stp to convergence to the correct path as the primary active FHRP node.

However when this topology cannot be applied especially with GLBP its suggested that stp disables the the correct l2 interconnect port in times of convergence in a deterministic manner so not to make a sub-optimal L2 switching path for the access-layer hosts towards each GLBP AVF.



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future

View solution in original post

Highlighted
Beginner

Re: GLBP and Loop-Free Topologies

Interesting. So Cisco limited GLBP's ability to work with looped networks to prevent potential network issues that come from undesirable STP changes during convergence? If I got what you were putting down, I think you cleared it up for me.
Highlighted
VIP Mentor

Re: GLBP and Loop-Free Topologies

Hello

Please review this link has have managed to find, It discuses relatively what i have explained here but in a much clearer way for you to understand  - here



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future

View solution in original post