Recently hit a frustrating issue with an Aruba 8360-48XT4C where our 100G single-mode LR4 optic wouldn't come up in port 1/1/49. The optic was fine—tested it in other switches—but this particular port combination had thermal constraints we hadn't accounted for.
Aruba 8360 switches have thermal design limitations when certain high-power 100G optics are used in specific port combinations, particularly the first 100G port (1/1/49) under certain environmental conditions.
The Problem
Port 1/1/49 kept showing down with our 100GBASE-LR4 transceiver, despite the optic working perfectly in other switches. Initial debugging suggested a hardware failure, but the real issue was thermal management.
# Port status showed this consistently:
8360-core# show interface 1/1/49
Interface 1/1/49 is down (Administratively up)
Hardware: Ethernet, MAC Address: aa:bb:cc:dd:ee:ff
Type: 100GBASE-LR4
Link-state: Down
Last link-state change: 2025-07-15 14:23:01.125 UTC
Transceiver: detected, 100G LR4 SFP+Root Cause Analysis
The 8360 series has specific thermal design considerations:
- Port layout: The first 100G ports (1/1/49-52) are closest to the main heat sources
- Airflow direction: Side-to-side airflow can create hot spots
- Optic power consumption: LR4 optics consume more power than SR4
- Ambient temperature: Our server room was running at 24°C
The Solution
Three approaches worked for us:
Moved the 100G link to port 1/1/52 (furthest from heat sources). Link came up immediately.
# Check thermal status first
8360-core# show system temperature
Temperature Status: Normal
Current Temperature: 42°C
Maximum Operating Temperature: 65°C
Thermal Shutdown Temperature: 75°C
# Verify optic compatibility in new port
8360-core# show interface 1/1/52 transceiver
Interface: 1/1/52
Transceiver: Present
Type: 100GBASE-LR4
Vendor: Aruba Networks
Temperature: 38.2°C (Normal)Long-term Solutions
- Improved cooling: Added supplemental rack fans targeting the switch intake
- Optic selection: Switched to lower-power SR4 optics where fiber distance allowed
- Port planning: Reserved 1/1/49-50 for lower-power connections
Monitoring
Added thermal monitoring to our network automation:
# Daily thermal check via SNMP
snmpwalk -v2c -c public 8360-core 1.3.6.1.4.1.47196.4.1.1.3.2.1.1.5
# Alert if any sensor > 50°C
if [[ $temp -gt 50 ]]; then
echo "ALERT: Switch thermal warning - $temp°C" | mail admin@sprintwave.co.uk
fiThis experience taught us to always check thermal design guides when planning 100G deployments, especially in dense configurations. The 8360 is a solid switch, but like all high-density gear, thermal management matters.