Two L2 link , backuo or load sharing?

[Ziggy74]

Hello,

I have in my site a L2 connection to the POP for the internet access, we will add a second L2 link to avoid the outage in case on down of the first L2 link.

 My questions are:

1) is better to use the second L2 link as backup ?

2) is better to use it with the first link main in sharing ?

3) in case of point 1 we have to use Spanning three  to ave second link available only when the first is down?

4) in case of point 2 ho i can set the load sharing?

Thanks in advance for your suggestions

Regards 

[Ziggy74]

Hi Seb,

thanks for your suggestion, i cannot get a 6500 for now.

I thought to use flexlinks , do you know it?

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3550/software/release/12-2_25_see/configuration/guide/swflink.html

Thanks

Regards

[Joseph W. Doherty]

I'm aware of flexlink, but I've never used that Cisco technology. Instead used Etherchannel, STP, or L3 to deal with multiple Ethernet links.

[Ziggy74]

Hi Seb,

in this case i cannot use Etherchannel as you know, STP will be the last option, do you have a L3 example to explain ?

Tnanks

Regards 

[Seb Rupik]

STP operates at Layer 2. 

You should be able to configure a triangle of links between the three switches and STP will provide you a loop free topology. To ensure it is optimal, for any SVI ensure that the VLAN root bridge is also on that switch.

If you reach the stage where you have a pair of links running to sw3 from both sw1 and sw2, then STP would successfully block one off the links in each pair. At this stage you would bundle the links into an etherchannel to make the all in a forwarding state.

cheers,

Seb.

[Ziggy74]

Hello Seb,

thanks for your replies suggestions, could you send me a suggestions about the  configuration ? I will test it in lab .

Thanks in advance

Regards

[paul driver]

Hello

---

@Ziggy74 wrote:

Hello,

I have in my site a L2 connection to the POP for the internet access, we will add a second L2 link to avoid the outage in case on down of the first L2 link.

 My questions are:

1) is better to use the second L2 link as backup ? - I would its better to try an utilize both links if applicable

2) is better to use it with the first link main in sharing ? - you could Load shared over both link with stp vlan/port/cost priorities

3) in case of point 1 we have to use Spanning three  to ave second link available only when the first is down? -  no you dont you could flex-link the backup port, thus negating stp completely for the two links

4) in case of point 2 ho i can set the load sharing? - you could use stp as in answer 2 or as suggested aggregate the links into a etherchannel

---

[Ziggy74]

Hello Paul,

can you suggest the configuratio for stp plus etherchannel .?

I prefer Flexlink then STP 

Thanks a lot

[paul driver]

Hello

Flex -link
int x/x

description Primary L2 link
switchport backup interface x/x

[Ziggy74]

Hello Paul,

sorry I mean configuration example for  STP.:)

Thanks

Regards

[paul driver]

Hello

It wont be as simple at that, as the config all depends on what stp mode your are running and how you are prioritizing your stp estate.

So my questions regrading this would be at present :
-What stp mode are you running for your lan network
- Do you have any no cisco switchs attaching to your network
- Do you a have  single stp root switch or dual stp root switches?