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 

[Seb Rupik]

Hi there,
If you are conecting two switches together with two links it makes to configure an Etherchannel as opposed to two seperate links runing STP resulting in one being blocked.

You will enjoy increased bandwidth and the event of a link failure there will be no disruption to service (assuming a single link can carry the traffic volume which was being carried by two).

Regarding the etherchannel hashing alogrithm, your selection this will be platform dependant. Since you are probably running a point-to-point link between the POP and switch/ router it doesn't make sense to use either src-mac or dst-mac. As it is outbound traffic dst-ip would probably be best.

cheers,
Seb.

[Ziggy74]

Hello Seb ,

thanks for your suggestions, I much appreciate it.
Ether channel is a valid solution , but if we change the scenario as the picture here in enclose, SPT  is the solution?

Thanks in advance

Regards

[Seb Rupik]

Hello agian,

In the new topology is there a path between SW1_site and SW2_site? If there isn't then your STP topology will not have any blocked ports.

If the two Site switches are connected with a VLAN being available on all devices, then depending on the location the Root Bridge you could have a sub-optimal STP topology. Assuming the router is the Root Bridge and all other link costs are equal then the path between SW1_Site and SW2_Site would be blocked. This would be OK and would allow both L2 links to be used.

However, if a device on SW1_Site needed to communciate with a device on SW2_Site it would need to go via the router and potential incur soe latency and bandwidth restrictions.

You ideal topology would be to have a Layer3 device at the site location, with a etherchannel to the Router. The routing for site VLANs would be done on the Layer3 device.

cheers,

Seb.

[Ziggy74]

Hello Seb,

thanks again.

So at the end i decided to use a 6500 in the site (I have it available) as your suggestion.

In the final picture can i configure a ether-channel on 6500 ? to have automatically backup once one link will be down?

Thanks in advance

Regards

Z

[Seb Rupik]

Yes, if you cannot create an etherchannel between the 6500 and the router, then the topology you have drawn will work with the router as the Root Bridge.

cheers,

Seb.

[Ziggy74]

Thank you Seb.

[Seb Rupik]

No problem.

Don't forget to mark this post as solved.

cheers,

Seb.

[Ziggy74]

Hello Seb,

yes i didn't try it until now but i will do when finished.

Thankjs a lot

[Ziggy74]

Hello Seb ,

hope this message finds you well.

Finally we know final the scenaro , it is in the diagram here in enclose.

My idea is etherchannel or VPC , do you agree?

Thanks

Regards

.

[Seb Rupik]

Hello again,

I still think you should have a link between SiteA sw1 and sw2, especially if you are doing the routing for SiteA VLANs on those switches.

In your current topology a host on VLAN-1 connected to sw1 would need to go via sw3 to reach a host on VLAN-1 connected to sw2. This is not optimal.

Assuming that all the routing is done on sw3, in the event on sw3 failing, hosts on sw1 and sw2 will not be able to communicate.

In my view add a link between sw1 and sw2. All SiteB VLANs should be routed on sw1 and sw2, use HSRP between them. Make the STP root-bridge for any VLAN on the same switch that routes that VLAN. Use RPVST.

...but to answer your immediate question, yes an Etherchanel would be ideal for the cross site links. A vPC if Sw3 supports it.

Cheers,

Seb.

[Ziggy74]

Hello Seb,

thanks for your reply, the sw3 i think doesn't support vPC , so etherchannel is the last solution available.

do you agere if i configure?:

portchannel 1 on sw1, interfaces g0/15 will be associated to this PO1

portchannel 1 on sw2  interfaces g0/16 will be associated to this PO1

portchannel 2 on sw3 inrtfaces g0/10 and interfaces g0/11 will be associated to PO2

Thanks

[Seb Rupik]

Your diagram doesn't include any switchport IDs, so I can't confirm what you are saying.

But...regarding sw1 and sw2, although there is nothing wrong in bundling single links into a port-channel, you gain nothing by it. You need at least two links bundled into a port-channel.

It also sounds like you are combining the incoming links into the same port-channel on sw3. This will not work as sw1 and sw2 are not part of the same virtual chassis, they are separate devices.

cheers,

Seb.

[Ziggy74]

Hello Seb,

waht is the real solution to avoid loops?

VPC : sw3 is not nexus so does' support it

PO:  Sw1 and sw2 are not stacked

Thanks in advance

[Joseph W. Doherty]

BTW, when using a 6500, if you desire to define an Etherchannel using different cards, and using QoS, if the cards have different QoS architectures, you need to add a command to allow them to bond. You also need to insure the ports are running at the same "speed", even if using the same card.