FlexLinks

Lessons Discussion
1

This topic is to discuss the following lesson:

https://networklessons.com/switching/flexlinks/

2

Rene,
Hi. In a normal working state, what does the interface status look like if one were to say issue a “show interface status” or “show interface F0/16” in this case?

Many thanks.

Thomas

3

Hi Thomas,

It should show something like “standby mode” line protocol down instead of up/up.

Rene

4

is there any reason to run flexlink rather than STP?

5

I think the only advantage is the convergence time, flexlinks are faster than RSTP.

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6

Hi Rene,

Can you explain what if failed link get backup, will it automatically switch over to active link.?

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7

Hi Ranjana,

Yes it will switch back to the active link.

Rene

8

Hi Rene,

ANY Ethernet Frame will not send to Backup link if receive then discarded , right ??

Flexlink can work with Many link ??

br//
zaman

9

Hi Zaman,

The backup link is not used at all…unless the primary link fails. One flexlink has 1 primary and 1 backup link, you can configure multiple flexlink pairs though…the maximum number depends on the platform.

Rene

10

Hei Rene,

Cisco says something else:

If port 1 goes down, port 2 comes up and starts forwarding traffic to switch C. When port 1 comes back up, it goes into standby mode and does not forward traffic; port 2 continues forwarding traffic.

But I Strongly agree with you! because i have done it on ME3400 live with customer:

When it was nothing connected to Gig 0/2 on ME3400:
GigabitEthernet0/1 GigabitEthernet0/2 <strong>Active Up/Backup Down</strong>

When he connected the lan cabel to Gig 0/2:
GigabitEthernet0/1 GigabitEthernet0/2 <strong>Active Up/Backup Standby</strong>

when he took Gig 0/1 out:
GigabitEthernet0/1 GigabitEthernet0/2 <strong>Active Down/Backup Up</strong>

when he connected Gig 0/1 back, For 5 sec the main interface was in standby mode:
GigabitEthernet0/1 GigabitEthernet0/2 <strong>Active Standby/Backup Up</strong>

Gig 0/1 took control:
GigabitEthernet0/1 GigabitEthernet0/2 <strong>Active Up/Backup Standby</strong>

Regards,
Jie

11

Thanks Rene for sharing this concept. But do you in real network people using flexlinks over STP?

Thanks
Abhihsek

12

Some environments such as industrial have weird policies like “No spanning-tree allowed anywhere.” In this case a network designer can get around the policy with flex links.

13

Some customers don’t like the overhead that STP causes on their CPU while computing its BPDUs. They want the entire cycle to be dedicated to the actual Users’ data forwarding. Therefore, they have to find something which consumes little to 0 load on the CPU. Flex links is their option

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