Tag: Reverse DNS

While doing a bit of technical research (read: running traceroute) for the post on IX Scotland, I came across this blast from the past…

So, not only do we have a bit of a blast from the past in the reverse DNS, but does this really make it look like Scotland is behind a L(3) (ex-BBN/Genuity) Fast Ethernet port?

Actually, it’s more of a testament to how infrequently ISPs check and update their reverse DNS zones, and sometimes how infrequently networks change their transit providers.

The “scotland” referred to here is actually going to be Brightsolid (the former Scotland On-line – changing it’s name more often than changing it’s upstream!), and if you look carefully at the latencies between the highlighted hop 5 and the previous hop 4, you’ll see that hop 5 isn’t actually in Scotland, but will be very close to hop 4 – so actually in Manchester itself. Hop 6 is actually the first hop in Scotland, 14 ms away.

Reverse DNS zones – that’s IP address to hostname lookup, rather than the other way around, which is more common – are notorious for being neglected, containing stale data or sometimes scarcely being populated at all.

Yet, they provide important diagnostic information. For instance, it’s not just the domain and customer info which is out of date, but I suspect the interface information is as well. It’s unlikely to be a Fast Ethernet port in this day and age.

Sadly, the situation seems to be even worse with IPv6. With those awkward long addresses, some just seem to be “not bothering” with reverse entries at all.

If you run a network, reverse entries are really useful tools to both your own netops folk and to your customers and peers, and deserve to be maintained.

Anyway, just a bit of trivia that caught my eye…