Re: Internet diameter?

Thu Nov 22 09:55:47 UTC 2018

On Thursday, 22 November, 2018 05:30, "William Herrin" <bill at herrin.us> said:

> Good question! It matters because a little over two decades ago we had
> some angst as equipment configured to emit a TTL of 32 stopped being
> able to reach everybody. Today we have a lot of equipment configured
> to emit a TTL of 64. It's the default in Linux, for example. Are we
> getting close to the limit where that will cause problems? How close?

If it's hop-count that's interesting, I think that raises a question on the potential for a sudden large change in the answer, potentially with unforeseen consequences if we do have a lot of devices with TTL=64.

Imagine a "tier-1" carrying some non-trivial fraction of Internet traffic who is label-switching global table, with no TTL-propagation into MPLS, and so looks like a single layer-3 hop today.  In response to traceroute-whingeing, they turn on TTL-propagation, and suddenly look like 10 layer-3 hops.

Having been in the show/hide MPLS hops internal debate at more than one employer, I'd expect flipping the switch to "show" to generate a certain support load from people complaining that they are now "more hops" away from something they care about (although RTT, packet-loss, throughput remain exactly the same).  I wouldn't have expected to break connectivity for a whole class of devices. 

Regards,
Tim.

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