U.S. East–West Coast Transmission Outage — Causes, Impacts, and Lessons Learned

Published: 2025-08-26  |  Source: Cogent Network Advisory

On August 26, 2025, Cogent’s backbone network in the United States experienced a series of outages, resulting in packet loss and latency for traffic between the East and West coasts. This article reviews the timeline, root cause, impact, and provides recommendations for network operators and service providers.

I. Event Highlights

  • Start: ~06:25 UTC, Aug 26, 2025
  • Resolution: ~06:55 UTC, Aug 26, 2025
  • Duration: ~30 minutes
  • Impact: Packet loss and latency on East–West transit traffic, affecting real-time/interactive services
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II. Root Cause (per operator)

  1. Main outage: Large fiber cut between Dallas and El Paso (P1 HD305374440) forced traffic onto northern alternate routes.
  2. Secondary limitation: Planned maintenance/troubleshooting on the Denver–Salt Lake path (HD305266873) reduced capacity, causing congestion and packet loss.

III. Impact & Symptoms

  • Increased latency and packet loss across backbone routes
  • TCP retransmissions and connection delays
  • Web page loading slowdown and occasional timeouts
  • Video/voice jitter and degraded experience
  • Possible disruption to cross-region backups/sync jobs

IV. Resolution & Recommendations

Cogent confirmed the affected links were restored and no further packet loss observed. Customers still affected should contact Cogent Support: 877-726-4368.

Recommended actions for network/service operators:

  • Multi-carrier redundancy: Maintain at least two upstream providers to reduce dependency on a single backbone.
  • Dynamic traffic engineering: Leverage SD-WAN, MPLS-TE, or automated BGP failover strategies.
  • Granular monitoring: Implement per-ISP/ASN packet loss, jitter, and utilization alerts.
  • Application resilience: Use retry, caching, and graceful degradation to minimize user impact.

V. Lessons Learned

  • Fiber cuts remain a recurring risk to backbone reliability.
  • Insufficient alternate capacity or overlapping maintenance amplifies impact.
  • Automated traffic engineering and rapid detection are critical to minimize end-user impact.
Note: If required, we can also provide BGP redundancy check scripts, Prometheus/Alertmanager rule templates, or a failover playbook tailored to your network.

© 2025 Network Engineering Blog — Based on Cogent’s official advisory. For further details, please refer to the original notice or contact Cogent support.