Uplink Saturation on a Single Link Despite Available Ports
An Aruba 2930F access switch connects to a distribution switch over a single 1 Gb uplink. During backups, the uplink saturates and users see latency. The access switch has two free 1 Gb ports (Gi1/23 and Gi1/24), and the distribution switch has matching free ports. The network uses RSTP. A proposal is to cable both free ports to the distribution switch to 'double the bandwidth.' The distribution switch ports are currently in VLAN 1 only; the access uplink carries VLANs 10, 20, and 30 as tagged.
1. Evaluate the proposal to simply cable both free ports. What will actually happen and why?
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Simply cabling two ports creates a Layer 2 loop between the switches. RSTP will block one of the new links (or possibly one of the existing paths) to keep the topology loop-free, so you will not get double bandwidth - you will get one active link and one discarding link. Worse, because the new distribution ports are in VLAN 1 only and the existing uplink carries VLANs 10/20/30 tagged, the new links would not even carry the right VLANs if they did forward. The result is no capacity gain and added complexity/risk.
Bandwidth scaling across parallel links requires link aggregation, not additional STP links.
2. Describe the correct configuration on both switches to aggregate the links and carry the required VLANs, and note one thing that can still limit throughput.
Read the worked answer
Create an LACP bundle on both ends with matching VLAN membership:
! Access switch
trunk 1/23-1/24 lacp
vlan 10,20,30
tagged 1/23-1/24
! Distribution switch (matching)
trunk <ports> lacp
vlan 10,20,30
tagged <ports>
Both ends must use LACP, match speed/duplex, and have identical tagged/untagged VLAN config. STP then sees one logical link, so both members forward.
Caveat: a single flow is hashed to one member link, so a single large backup stream may still be limited to ~1 Gb. Aggregation increases aggregate capacity and improves multi-flow distribution, but does not make any single flow faster. Also confirm the distribution side has enough backplane/uplink capacity so you are not just moving the bottleneck.