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DEMO: LACP Port Priority

LACP port priority controls which physical links are activated or suspended within an EtherChannel when the group exceeds a switch's maximum supported links. Lower priority values increase the likelihood a port will be selected as active, while higher values make suspension more likely.

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About this video

EtherChannel allows multiple physical links to be aggregated between switches for increased bandwidth and redundancy. However, when the number of configured links exceeds what one of the switches can actively support, LACP must determine which ports remain active and which are placed in standby. This is controlled through LACP port priority, a per-interface value that influences selection when the bundle must be trimmed to fit hardware limitations. LACP port priority values range from 0 to 65,535, with a default of 32,768. A lower value signals higher priority, making that port more likely to be chosen as an active member of the EtherChannel. A higher value reduces a port's likelihood of selection, effectively making it a standby candidate. Configuration is straightforward and applied at the individual interface level in global configuration mode using the lacp port-priority command followed by the desired numeric value, giving network administrators precise control over which physical links carry traffic when constraints require the channel to operate below its maximum configured capacity.

What you'll learn

What's covered

LACP Port Priority

Aligned to

Cisco CCNA
2.4 Configure and verify Layer 2/Layer 3 EtherChannel (LACP)

Key terms

EtherChannel
Cisco's implementation of link aggregation that bonds multiple physical links into a single logical channel to increase bandwidth and redundancy.
Link Aggregation Control Protocol
LACP
An IEEE 802.3ad protocol that automatically negotiates and manages the bundling of multiple physical Ethernet links into a single logical link aggregation group. LACP enables dynamic detection of compatible links and provides failover if individual member links go down.
LACP Port Priority
A configurable value (0–65535) assigned to a switch interface that determines which physical links are active or placed in standby within an EtherChannel bundle; lower values indicate higher priority.
Bandwidth
The maximum rate of data transfer across a network path, typically measured in bits per second.
Switch
A network device that connects devices within a LAN and forwards traffic based on MAC addresses.

Topics

Lacp Etherchannel Port Priority Link Aggregation Cisco Ios Switching Networking

Transcript

When you need to pick which links stay up

There are times when EtherChannel that's using multiple links may not be able to utilize all of the links, that it might need to be able to choose some of those links to shut down or not utilize as part of the EtherChannel. In that case right there, we may need to specify which channels are going to be used, which ports are going to be used and which ones aren't going to be used. In that case we would use an LACP priority.

Let's run through a little scenario here. Let's say we have two different switches and we need more bandwidth between the switches, so instead of just two links, let's say we're going to do a total of eight. However, this switch right here maybe supports eight and this one right here only supports six, and so therefore what's going to happen is it's going to shut down two of the links that are on here. But let's say we want to prioritize which links we are going to shut down. We're going to use a port priority over that.

Setting the port priority

The commands for this are really quite simple. All I need to do here is, on the switch, I'm going to get into the global configuration mode. Within there I'm going to get into my interface, so in this case right here we'll do fa1 043, which is part of a channel group here. Then what we'll do is set the priorities, so lacp, and we'll do port-priority, and then I'm going to do a question mark and we'll take a look at this.

We're setting a number anywhere between 0 and 65,535. The lower the number, the higher priority, which means that it'll choose that over other ones, so that one being the one that's going to be up.

The default for this is 32,768. So let's say I want this channel to be utilized first: then I would set it anything below that 32,768, so maybe I'd do just 32,000 and then hit enter. Now it's more likely that it's going to choose this over another port to be up and running. Or if I want to make it less likely to choose this, then I would do anything above 32,768, so let's do 33,000 and hit enter. Now it's less likely to choose this one.

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