🟠 High   ⏱ 5–30 min  Last verified: 19 May 2026
Affected versions: RHEL 10.0 RHEL 10.1

📖 ~1 min read

Table of contents
  1. Symptom & Impact
  2. Environment & Reproduction
  3. Root Cause Analysis
  4. Quick Triage
  5. Step-by-Step Diagnosis
  6. Solution – Primary Fix
  7. Solution – Alternative Approaches
  8. Verification & Acceptance Criteria
  9. Rollback Plan
  10. Prevention & Hardening
  11. Related Errors & Cross-Refs
  12. References & Further Reading

Symptom & Impact

Intermittent packet loss and session resets occur on VLAN interfaces under normal load.

Environment & Reproduction

Observed where uplink and host VLAN profiles use inconsistent MTU values.

nmcli connection show
ip -d link show

Root Cause Analysis

MTU mismatch causes fragmentation drops and path MTU blackholing.

Quick Triage

Confirm active profile, link state, and dropped packet counters.

systemctl status NetworkManager
nmcli -f NAME,UUID,TYPE,DEVICE connection show --active
firewall-cmd --get-active-zones
getenforce
journalctl -u NetworkManager -n 80 --no-pager

Step-by-Step Diagnosis

Compare configured MTU with switch and upstream policy.

nmcli -f 802-3-ethernet.mtu,802-1q.id connection show vlan10
ip -s link show vlan10
ping -M do -s 8972  -c 3
Illustrative mockup for rhel-10 — vlan_mtu_dropouts
Packet loss due to VLAN MTU mismatch — Illustrative mockup — Progressive Robot

Solution – Primary Fix

Set consistent MTU on parent and VLAN profiles, then cycle connection.

Still having issues? Our IT Solutions & Services team can diagnose and resolve this for you. Get in touch for a free consultation.

sudo nmcli connection modify bond0 802-3-ethernet.mtu 9000
sudo nmcli connection modify vlan10 802-3-ethernet.mtu 9000
sudo nmcli connection down vlan10 && sudo nmcli connection up vlan10
sudo systemctl restart NetworkManager
Illustrative mockup for rhel-10 — vlan_mtu_aligned
Aligned MTU and stable VLAN link — Illustrative mockup — Progressive Robot

Solution – Alternative Approaches

Use conservative MTU 1500 where intermediate devices cannot support jumbo frames.

sudo nmcli connection modify vlan10 802-3-ethernet.mtu 1500
sudo nmcli connection up vlan10

Verification & Acceptance Criteria

No packet drops over sustained test and application sessions remain stable.

ping  -c 50
ip -s link show vlan10
journalctl -u NetworkManager -n 40 --no-pager

Rollback Plan

Revert to previous profile MTU and re-activate network connection.

sudo nmcli connection modify vlan10 802-3-ethernet.mtu 1500
sudo nmcli connection up vlan10

Prevention & Hardening

Add MTU validation checks to network change workflows and host onboarding.

nmcli -f NAME,802-3-ethernet.mtu connection show

Related to VXLAN overlays, ICMP filtering, and fragmented traffic drops.

Related tutorial: View the step-by-step tutorial for rhel-10.

View all rhel-10 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

NetworkManager VLAN configuration and MTU troubleshooting references.

Need Expert Help?

If you cannot resolve this yourself, our team offers hands-on Server Management, Managed IT Services, and flexible Support Plans. Contact us today — we respond within one business day.