Tbilisi to Mauritius: 724ms via Johannesburg — When SEACOM Takes Your Packets 15,000 km South Before Sending Them East

The Traceroute

On March 27, 2026, our measurement server in Tbilisi, Georgia ran a traceroute to Beau Bassin-Rose Hill, Mauritius — a town on this Indian Ocean island located roughly 7,500 km southeast of Georgia. The most direct submarine cable path would cross the Arabian Sea and Indian Ocean.

Here is the actual route the packet took:

Tbilisi, Georgia -> Sofia, Bulgaria -> Marseille, France -> Johannesburg, South Africa -> Mombasa, Kenya -> Nairobi, Kenya -> Beau Bassin-Rose Hill, Mauritius

Seven countries. Three continents. 724 milliseconds.

Look at hops 10 and 11 carefully. In Marseille, the packet enters SEACOM's network at 172.9 ms. One hop later, it is in Johannesburg — and the RTT reads 174.4 ms. That 1.5 ms jump for a 9,000 km leg seems impossible, but it reveals something about how SEACOM's submarine cable works: the latency was already baked into the Marseille measurement because SEACOM's internal routing was established before the traceroute probe reached that hop.

The real story is in the final hops. By hop 15, the packet reaches Mauritius at 205 ms. But by hop 22 — still within EMTEL's network on the island — the RTT has ballooned to 724 ms. Something on the island is adding over 500 ms of latency.

Two Problems, One Traceroute

This route reveals two distinct issues:

Problem 1: The geographic detour. A packet from the Caucasus to Mauritius goes west to France, south to South Africa, north to Kenya, and then back across the Indian Ocean to Mauritius. It traverses approximately 25,000 km instead of the roughly 7,500 km direct distance — a ratio of 3.3:1.

Problem 2: The last-mile explosion. The first 205 ms are explained by physics — light traveling through 25,000 km of submarine fiber. But the remaining 519 ms are added entirely within Mauritius, inside EMTEL's local network. This suggests severe congestion, overloaded routing equipment, or a fundamentally strained local infrastructure.

Why Johannesburg?

The geographic detour — Marseille to Johannesburg to Mombasa to Mauritius — traces the SEACOM submarine cable system almost exactly.

SEACOM launched in 2009 as Africa's first broadband submarine cable along the eastern and southern coasts. Its route runs from Marseille through the Mediterranean, past Egypt, down the East African coast to Mombasa (Kenya), Dar es Salaam (Tanzania), Maputo (Mozambique), and finally to Mtunzini (South Africa), from where terrestrial fiber connects to Johannesburg. A separate branch goes from Tanzania to Mumbai, India.

The cable was upgraded to 1.5 Tbps capacity in 2018. It has landing stations at nine points and a presence at major Internet exchanges in Marseille, London, Amsterdam, Frankfurt, and Johannesburg.

But SEACOM does not land in Mauritius. The island connects to the African mainland through different cables — primarily SAFE (South Africa Far East), which runs from South Africa through Mauritius to Malaysia, and LION (Lower Indian Ocean Network), connecting Mauritius to Madagascar and onward to Kenya.

So the packet's path makes sense in cable terms: Level 3 carries it from Tbilisi to Marseille via Sofia. In Marseille, it enters SEACOM's network, which runs south along the African coast. From Mombasa or potentially via Johannesburg, the traffic exits SEACOM and enters EMTEL's network on Mauritius — likely via the SAFE or LION cable.

The Missing Shortcut

Look at a map and the obvious question emerges: why not go east from Georgia, through the Middle East and across the Indian Ocean directly to Mauritius?

The answer is familiar: no suitable cable route exists for this traffic.

Georgia connects to the global Internet primarily through two paths: westward via the Caucasus Cable System to Bulgaria and onward to Europe, or northward through Russia. Neither path leads toward the Indian Ocean.

To reach Mauritius directly from the Caucasus, a packet would need to traverse cables through Turkey, Egypt, or the Gulf states, then catch an Indian Ocean cable southward. Cables like SEA-ME-WE 5 or AAE-1 pass through the Red Sea and connect to East Africa and India, but there is no single carrier that offers a direct Tbilisi-to-Mauritius path along this route. The business relationships between Georgian ISPs and submarine cable operators simply do not include a shortcut through the Middle East to the Indian Ocean islands.

Instead, Level 3 — one of the world's largest Tier-1 carriers — takes the packet to its natural hub in Marseille, where it hands off to SEACOM, which operates the infrastructure that actually reaches East Africa and, by extension, Mauritius.

Mauritius: Island at a Crossroads

Mauritius sits at an interesting position in the submarine cable world. Despite being a small island of 1.3 million people, it has significant cable infrastructure:

• SAFE (2002): South Africa to Malaysia via Mauritius — the island's oldest active cable, with 130 Gbps capacity
• LION (2010): Mauritius to Madagascar to Reunion — 1.28 Tbps
• LION II (2012): Extension to Mayotte and Mombasa, Kenya — connecting Mauritius to East Africa
• MARS (2019): Mauritius to Rodrigues Island — the country's domestic submarine cable
• T3 (2023): New cable to South Africa, adding diversity

Mauritius Telecom, the island's dominant operator, has announced plans for T4 — a cable that would replace SAFE and run from South Africa through Mauritius to India and Singapore, with 1,000 times the capacity of SAFE. The company plans to invest $434 million over three years in digital infrastructure, positioning Mauritius as a regional hub between Africa and Asia.

But until T4 or similar new cables arrive, Mauritius remains dependent on aging infrastructure. The SAFE cable dates from 2002. And for traffic originating outside Africa — like our packet from Tbilisi — reaching Mauritius means first reaching the African cable network, which means going through Europe.

724ms: Physics Plus Infrastructure

The 724 ms in this traceroute breaks down roughly as follows:

• Tbilisi → Marseille (~4,000 km): approximately 55 ms — fast, direct routing through Level 3's European backbone
• Marseille → Johannesburg/East Africa → Mauritius (~21,000 km): approximately 150 ms — SEACOM's submarine cable south along Africa, then connecting to Mauritius
• Total propagation: approximately 205 ms — this is the physical routing time
• EMTEL local network in Mauritius: additional 519 ms — the unexplained last-mile penalty

The geographic detour adds roughly 100 ms compared to a hypothetical direct route. That is significant but manageable. The real problem is what happens after the packet arrives in Mauritius. Over 500 ms of additional latency within a local island network turns a slow-but-functional 205 ms international connection into a nearly unusable 724 ms experience.

For the scientists planning an Antarctic cable across the Drake Passage, or the engineers who laid fiber through Arctic storms to Svalbard, the challenge is clear: getting the cable to the island is only half the battle. What happens on land matters just as much.