European Network Redundancy Absorbs Baltic Cable Cuts
Submarine and terrestrial cable cuts frequently cause measurable disruptions to Internet connectivity, especially when the affected cable represents a single point of failure for a network, city, or country. However, two recent cable cuts in the Baltic Sea region produced little-to-no observable impact to the affected countries, largely due to the substantial redundancy built into European Internet infrastructure.
BCS East-West Interlink Cut
On Sunday, November 17 2024, the BCS East-West Interlink submarine cable connecting Sventoji, Lithuania and Katthammarsvik, Sweden was reportedly damaged around 10:00 local time (08:00 UTC). According to a Data Center Dynamics article, the CTO of Telia Lietuva, the operator of the cable, noted that the cable carried roughly a third of Lithuania's Internet capacity, but that other routes carried the rest.
Cloudflare Radar traffic volume data showed no apparent impact to either country at the time of the damage. NetFlows graphs, which track the number of bytes Cloudflare sends to users in response to their requests, reflected no sudden drop in traffic for Lithuania or Sweden.
Internet quality metrics for both countries showed variations in bandwidth and latency throughout the day, but no sudden anomalies aligned with the cable cut. While Sweden's latency graph showed an increase, it began before the reported damage time, resembled a pattern from earlier in the day, and was accompanied by a rise in measured bandwidth, making a connection to the cable cut unlikely.
From a routing perspective, BGP announcement activity was observed on Telia Lietuva's autonomous systems around the time of the incident, likely reflecting the re-routing of traffic referenced in the article. Notably, no change in announced IP address space was visible for those autonomous systems, indicating no loss of connectivity as capacity shifted.
The resilience enjoyed by these two countries is visible in their connectivity options. According to submarinecablemap.com, Lithuania is connected to neighboring Latvia and to the Swedish mainland, while over 20 submarine cables land in Sweden, linking it to multiple countries across Europe. Additionally, network providers can leverage terrestrial fiber connections to adjacent countries, as illustrated by Arelion's European network map.
C-Lion1 Cut
Less than a day later, the C-Lion1 submarine cable connecting Helsinki, Finland and Rostock, Germany was reported damaged in the early hours of Monday, November 18. Cinia, the cable's owner, stated that the cable stopped functioning at approximately 02:00 UTC.
Once again, Cloudflare Radar graphs showed no apparent impact to traffic volumes in either affected country at the time of the damage. Finland's graphs showed fewer bytes transferred and fewer HTTP requests week-on-week, but this difference appeared before the cable cut, and the trend line did not change after 02:00 UTC, suggesting the events were unrelated.
While volume-based metrics suggested unaffected connectivity, Internet quality data revealed a brief but interesting change for Finland around the reported damage time. Just after midnight, median measured bandwidth rose from a consistent ~50 Mbps to peak at just over 200 Mbps around 03:00 UTC. Concurrently, median latency fell from around 30 ms to a low of 13 ms, also at approximately 03:00 UTC. Bandwidth returned to normal around 06:00 UTC, while latency took roughly two more hours to normalize. These improvements could indicate traffic re-routing to paths with better connectivity to measurement endpoints, but the shifts began before the cable damage and recovered soon after, making that explanation unlikely.
In Germany, a brief minor increase in median bandwidth peaked around 02:45 UTC, with no notable latency changes observed.
BGP activity for top autonomous systems in Finland and Germany showed no notable announcements around 02:00 on November 18, and country-level aggregated announced IP address space remained unchanged, indicating normal routing operations.
Finland and Germany also have significant submarine cable redundancy. Over 10 cables land in Finland and nearly 10 in Germany, including Atlantic Crossing-1 (AC-1), which connects to the United States via two distinct paths. Terrestrial fiber routes from providers like Arelion and eunetworks show multiple redundant pathways within both countries, as well as cross-border connections to neighboring nations, further contributing to network resilience.
Redundancy as Best Practice
Cable cuts often cause significant and lengthy disruptions, particularly when infrastructure represents a concentrated vulnerability for a network, region, or country. The time required to marshal repair resources and locate the damage extends these outages. While financial or geographic constraints make it impractical in some cases, building redundant and resilient network architecture at multiple levels is a best practice. This involves distributing traffic across multiple physical cables, whether submarine or terrestrial, connecting to multiple peer and upstream providers, and avoiding single points of failure in core Internet resources such as DNS servers.
