Internet woes in SA: Subsea cable faults and terrestrial failures

A double cable fault affecting the EASSy and Seacom cables may only partly explain the recent internet issues in South Africa. INX-ZA chair Edrich de Lange mentioned several terrestrial cable failures, reducing capacity between Johannesburg and Cape Town. Liquid Intelligent Technologies confirmed subsea faults, but internet exchange points only saw a drop in traffic hours later. Netflix withdrew its network prefixes, causing rerouting, possibly due to terrestrial cable failures. Netflix restored its prefixes later that night.

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By Jan Vermeulen

A double cable fault affecting the EASSy and Seacom cables may only be part of the reason Internet users in South Africa experienced problems with Netflix, Disney+, and other services on Sunday.

INX-ZA chair Edrich de Lange told MyBroadband that several terrestrial cable failures also occurred, reducing capacity between Johannesburg and Cape Town.

INX-ZA is a community-run Internet exchange point operator and autonomous division of the Internet Service Providers’ Association.

Its Johannesburg Internet Exchange is the oldest Internet exchange point in South Africa, boasting 100% uptime since 1996.

De Lange’s explanation accounts for the cable faults already being confirmed much earlier on Sunday afternoon, while users in South Africa only started reporting problems at around 17:00.

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Liquid Intelligent Technologies group CTIO Ben Roberts confirmed on Twitter at 13:44 that all subsea capacity between East Africa and South Africa was offline.

Roberts said there was a confirmed fault on the EASSy cable and that they were observing a fault on the Seacom cable that occurred at the same time.

EASSy is a 10,000km undersea fibre optic cable system connecting countries in Eastern Africa to the rest of the world.

Seacom confirmed it was also impacted by a fault. Seacom offers fibre-optic pairs from Mtunzini in South Africa to a point of presence in Marseille.

However, while both submarine cable faults were confirmed early in the afternoon, South Africa’s Internet exchange points only saw a substantial drop in traffic from around 16:40.

The following chart from Teraco-run Internet exchange point operator NAPAfrica shows the dip clearly, along with a steady recovery over the period when the evening peak is usually highest.

According to INX-ZA and NAPAfrica, this time coincides with Netflix’s withdrawal of its network prefixes from South Africa’s Internet exchange points.

Disney+ viewers also reported experiencing buffering during the evening.

Network prefixes are groups of Internet Protocol (IP) addresses that are clustered together to make routing traffic to them easier.

By withdrawing its prefixes, Netflix forced traffic that would usually flow through Internet exchange points to be rerouted elsewhere.

De Lange explained that traffic instead went to Netflix caches hosted by the local ISPs themselves, their transit providers, or to caches hosted in networks such as ZANOG.

On rare occasions, Netflix traffic would have been rerouted to an international cache.

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“From that perspective, there was minimal impact to the streaming for well-connected networks,” De Lange told MyBroadband.

However, the question still remains — why did Netflix only withdraw its prefixes several hours after the faults on Seacom and EASSy?

“I suspect this was not only related to the subsea failures,” De Lange told MyBroadband.

De Lange said they saw a terrestrial cable failure at around 16:48 that affected traffic between Cape Town and Johannesburg.

“I know of two IP transit providers who rerouted their traffic from Johannesburg via Durban to Cape Town,” he said.

“This naturally caused a capacity crunch for certain providers.”

De Lange surmised that this could’ve led to providers like Netflix withdrawing their traffic from exchange points, as the times match very closely.

Netflix restored its prefixes by later that same night.

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“Ultimately, the content delivery networks need to protect the quality of the content they provide, and if a node has a problem, it will usually reroute automatically,” explained De Lange.

For example, if a provider sees packet loss to the rest of their network via a specific node, that would cause many other issues, especially for live-streamed video.

Better to drop the problematic node and route traffic around it.

“They were fairly quick to get it back up and running after they investigated and rerouted,” De Lange noted.

MyBroadband contacted Netflix for comment, but it did not provide feedback by publication.

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This article was first published by My Broadband and is republished with permission