Options

# AD vs FD with variance clarification

Member Posts: 273

Path 1:

[R1] ======= [R2] ======= [R3] ======= [R4]
.............20...................25.....................20.................

Path 2:

[R1] ======= [R5] ======= [R6] ======= [R4]
.............10....................10....................10................

Path 3:

[R1] ======= [R7] ======= [R8] ======= [R4]
...............15..................10....................5..................

FD

[1-2-3-4] = 20 + 25 + 20 = 65 {AD of 45 > FD of successor 30 = not feasible successor(?)}
[1-5-6-4] = 10 + 10 + 10 = 30 {Lowest FD, so Best path = successor}
[1-7-8-4] = 15 + 10 + 5 = 30 {AD of 15 < FD of successor 30 = Feasible successor(?)}

[1-2-3-4] = 25 + 20 = 45
[1-5-6-4] = 10 + 10 = 20
[1-7-8-4] = 10 + 5 = 15

So, if variance is set to 2 and the FD of the successor is 30, then 30 x 2 = 60. Therefore any FS with an FD less than or equal to 60 is a path used for load balancing?

(So final paths with variance 2 are:
[1-5-6-4]
[1-7-8-4])

Is this correct?? (I hope what I displayed makes sense)

• Options
Member Posts: 1,614 ■■■■□□□□□□
I'm a bit tired so bear with my answer. Basically the variance command will only load balance on another path as long as that paths AD is lower then the current best paths FD. So yes you are correct with this statement {AD of 15 < FD of successor 30 = Feasible successor}
• Options
Mod Posts: 11,962 Mod
Kind of hard to follow along without a diagram, but it seems your math is correct.
An expert is a man who has made all the mistakes which can be made.
• Options
Member Posts: 1,340 ■■■■□□□□□□
Path 1 has an AD > the FD of Paths 2 and 3, so it would not be a Feasible Successor and would not be used for Load Balancing.
R&S: CCENT CCNA CCNP CCIE [ ]
Security: CCNA [ ]
Virtualization: VCA-DCV [ ]