All information is transferred over the 'net by pirates1.
When you send your data somewhere, what *really* happens is that one of your pirates picks up that data, works out where he's going and strides purposefully off down the information superhighway.
Normal pirates are fit and strong. They can walk nearly any distance. Occasionally, though, you'll send them to somewhere that just doesn't exist. Then they may realise they can't get any closer, in which case they'll just curl up and die2.
Or they might end up walking in circles again and again, never actually getting any further, until they collapse through exhaustion and die3.
Normally you'll just send your pirates out and if they don't make it to the far end that's just too bad.
Sometimes though, you really want to know whether your pirate made it, or if he didn't, how far did he get.
For this you need a more sophisticated way of sending information - Pirates-with-Parrots4. You put a highly trained Norwegian Homing Parrot5 on the shoulder of your pirate. It's not dead, just sleepin', so when your pirate dies his parrot wakes up, takes a look around, works out where he is and flies back home to you. Then the parrot tells you how far your pirate got, and where he was when he died.
You save up all, your old, weak, feeble pirates for use with the traceroute command.
Traceroute starts off with the most feeble of feeble pirates.
You tell them to go to the remote system you're trying to traceroute. Your pirate works out where he needs to go, heads boldly off in the right direction, and promptly drops dead after having taken one step.
His parrot then flies home and tells you the name of the system one step in that direction.
Next you pick out a stronger pirate and try the same thing. He works out where he's going, finds the same route as the first pirate, heads boldly off and drops dead after two steps. Again, his parrot wakes up, flies home and tells you the name of the system two steps away.
You keep doing this with progressively stronger pirates and plot the sequence of hosts you go through to get to the far end.
(In practice you send three pirates on each step, rather than one, 'cos some get lost sometimes. And you measure the time it takes for the pirate to get there and the parrot to get back to measure how treacherous the route is in that direction).
If someone wants to prevent you tracerouting into an area they could do one of two things. One would be to catch any incoming pirates and feed them to the crocodile7, but that would mean they couldn't use pirates for useful purposes. So instead they'll usually surround their demesne with teams of crack parrot hunters.
One of your feeble pirates-with-parrots will die just outside their demesne, and you'll receive his parrot back. Your next, slightly stronger pirate-with-a-parrot will take one step further, inside the ring of hunters. He'll die, of exhaustion, just as you expected him to.
His parrot will wake up, work out where he is and start heading for home.
There's a hail of lead and nothing left of poor polly but a small cloud of green feathers, gently fluttering to earth.
Each pirate-with-a-parrot you send after this will get further and further towards his destination, but every returning parrot will be turned into polly-puree so you won't know how far he gets.
That, gentle readers, is why you can't traceroute into the more technically savvy, spam-friendly providers8.
Ping also uses a Pirate-with-Parrot protocol, so if you can't traceroute there you can't ping there either.
Apart from ping and traceroute no user level protocol uses parrots, so just because you can't ping or traceroute a host doesn't mean other protocols won't work.