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Cisco announces new innovations in SD-WAN, ISRs, SD-WAN Services, and Catalyst 9000 Series switches


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Beginner

LACP load balancing in 2 switches part of 3750 stack switch

Hi,

Can I configure LACP with 2 network ports, one port going to switch 1 and second port going to switch2 and have active active

configuration so that load is shared across 2 links.  switch1 and switch2 are two switches in a Cisco 3750 stack configuration.

Connected host is a Solaris host.  I know LACP will work with active active configuration if both ports are connected to same switch and

also if both switches are Nexus switch, then if each network port goes to different switch, still we can configure LACP load balancing

with Solaris hosts.  Your inputs are highly appreciated and thanks in advance.

2 ACCEPTED SOLUTIONS

Accepted Solutions
Hall of Fame Cisco Employee

LACP load balancing in 2 switches part of 3750 stack switch

Hello Subin,

If your two 3750 Catalysts are stacked together then absolutely yes, you can create an EtherChannel with physical ports being connected to different switches in a single stack. Sometimes, this configuration is called Cross-Stack EtherChannel. All switches in a single stack behave like a single big switch, so from the EtherChannel point of view, its rule of "all ports being connected to a single switch" is not violated.

Best regards,

Peter

Hall of Fame Cisco Employee

LACP load balancing in 2 switches part of 3750 stack switch

Hello Subin,

Yes, this configuration will work. Please proceed with the configuration and keep us informed.

As I mentioned previously, for most control and data plane protocols and mechanisms including LACP and EtherChannel (Link Aggregation), a stack composed of several Cat3750 switches behaves as a single switch. Therefore, all protocols and mechanisms that you can use towards a single neighbor (such as an EtherChannel) can also be used towards a switch stack.

Best regards,

Peter

6 REPLIES
Hall of Fame Cisco Employee

LACP load balancing in 2 switches part of 3750 stack switch

Hello Subin,

If your two 3750 Catalysts are stacked together then absolutely yes, you can create an EtherChannel with physical ports being connected to different switches in a single stack. Sometimes, this configuration is called Cross-Stack EtherChannel. All switches in a single stack behave like a single big switch, so from the EtherChannel point of view, its rule of "all ports being connected to a single switch" is not violated.

Best regards,

Peter

Beginner

LACP load balancing in 2 switches part of 3750 stack switch

Thanks Peter.  Want to confirm once again.  I have attached picture of this scenario.

Solaris 11.1 host has two network interfaces, each of which is going to a different 3750 switch

which are stacked.  Please let me know whether LACP active active configuration will work

in this case.  Thank you.

Beginner

LACP load balancing in 2 switches part of 3750 stack switch

Hall of Fame Cisco Employee

LACP load balancing in 2 switches part of 3750 stack switch

Hello Subin,

Yes, this configuration will work. Please proceed with the configuration and keep us informed.

As I mentioned previously, for most control and data plane protocols and mechanisms including LACP and EtherChannel (Link Aggregation), a stack composed of several Cat3750 switches behaves as a single switch. Therefore, all protocols and mechanisms that you can use towards a single neighbor (such as an EtherChannel) can also be used towards a switch stack.

Best regards,

Peter

Beginner

LACP load balancing in 2 switches part of 3750 stack switch

Thanks Peter, this implementation will start only after 1 month, I will update this thread with result, then.

Beginner

Re: LACP load balancing in 2 switches part of 3750 stack switch

Hello Peter, 

 

I have a similar query on the given above situation. What will happen to if the MLAG break between the switches ( between NAS SW switches )and when system id changes for LACP. In the packet capture we see the System ID has changed for LACP on the VMware side. Which NIC will go down or the VMware side , is it suppose to go down also or not ? Attaching the topology for reference as well . 

 

MC_LAG issue.png

 

Regards,

UJ

 

 

 

 

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