[ih] TTL [was Exterior Gateway Protocol]

[tony.li at tony.li]

Hi Brian,

> I was taught many years ago that the TTL field (renamed Hop Limit in IPv6) was intended only as a last resort method of loop prevention.
> 
> a) Is that accurate?
> b) Has it ever saved the Internet?


Well I can’t speak to original intent.  Has it saved the Internet?  No. Has it saved some links (and thereby some networks and some jobs)?
Absolutely. Routing loops happen every day. Yes, most of them are micro-loop transients that happen while our IGPs converge. However,
some of them are far more serious: we allow people to create static routes. If you create a loop with those and there’s no TTL you’re in
for a Bad Day.

Was it worthwhile? Totally.

Tony