Hurricane Dorian, The Bahamas, and BGP

Hurricane Dorian has been a prominent fixture in the news for the past 10 days. Your author lives in Florida, and thus Dorian has been an unavoidable news item of late. Team Cymru folks in Florida are all safe and unscathed.

Hurricane Dorian left Florida with minimal impacts, but not so for The Bahamas. The most important concern now is human life and living conditions, no doubt. Our thoughts and prayers are with the people of The Bahamas.

The Dorian impacts left your author wondering: Can network data reveal some truths about the impact to the Bahamas? In our industry, we are data driven. What does BGP data show?

BGP Changes

Among the many data sets Team Cymru collects, we record several BGP related data points. BGP is the single most important protocol controlling how the Internet works.

First, we use ASes owned by Bahamian networks to look for changes in availability via BGP. Figure 1 shows fluctuation that could be Dorian related.

Figure 1

The above shows snapshots of prefixes seen at two hour intervals. This shows a relatively quick recovery of most advertised prefixes.

Next, we look at the timing and counts of announcements and withdraws for prefixes GeoIP says are in The Bahamas. Figure 2 shows fluctuations that could be Dorian related.

Figure 2

Here, we see several announcements and withdraws taking place. The large spike was a short-lived outage. When comparing this spike to Figure 1, we can see the spike recovered very quickly, such that a two hour time window does not show this impact.

Conclusions

Most networks did not disappear from BGP during and following Dorian hitting The Bahamas. This is impressive, given the storm’s direct hit on two major islands of The Bahamas.

This is also promising. It appears that communications networks may be available within The Bahamas. Communications is essential to coordination of recover efforts.

What we know from BGP is not the full story, however. We can not assert that these routes confirm anything about the ‘on the ground’ connectivity from within The Bahamas. Physical network architecture is unknown to us through BGP data alone. Still, there is reason for hope.

BGP is the starting point to Internet connectivity for end point networks. If BGP showed more problems, it could indicate more severe core networking issues. The Bahamas have a lot to handle, thankfully BGP shows that core networks may be substantially operational.

The Bahamas Networks and Methods

In this analysis, we use two different methods to determine what networks are in The Bahamas.

AS Method: For this method, we use ASes allocated to the Bahamas by ARIN: 8014, 15146, 18635, 19128, 19377, 26855, 33035, 58677, 394601.

GeoIP Method: For this method, we use addresses determined to be in The Bahamas based on GeoIP data. In our experience, GeoIP data sources are not great for our purposes when applied to IPv6. Thus, for IPv6 addresses, we use the ARIN allocated IPv6 blocks.

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