<font face="arial" size="2"><p style="margin:0;padding:0;font-family: arial; font-size: 10pt; overflow-wrap: break-word;">On Thursday, 22 November, 2018 05:30, "William Herrin" <bill@herrin.us> said:</p>
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<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; overflow-wrap: break-word;">> Good question! It matters because a little over two decades ago we had<br />> some angst as equipment configured to emit a TTL of 32 stopped being<br />> able to reach everybody. Today we have a lot of equipment configured<br />> to emit a TTL of 64. It's the default in Linux, for example. Are we<br />> getting close to the limit where that will cause problems? How close?<br /><br /></p>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; overflow-wrap: break-word;">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.</p>
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<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; overflow-wrap: break-word;">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.</p>
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<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; overflow-wrap: break-word;">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. </p>
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<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; overflow-wrap: break-word;">Regards,</p>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; overflow-wrap: break-word;">Tim.</p>
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