The RFC doesn't give any indication that a router needs to anticipate how long the next hop will take to decrement the TTL as it just refers to processing time.
Actually, it does. In several places. Search for "time to live" (case insensitive) in the RFC. You'll find that it is quite clear that the TTL is intended to be the maximum total datagram lifetime, so obviously a router will have to account for transmission delays.
For example, see page 30 (emphasis mine):
Time to Live
The time to live is set by the sender to the maximum time the
datagram is allowed to be in the internet system. If the datagram
is in the internet system longer than the time to live, then the
datagram must be destroyed.
This field must be decreased at each point that the internet header
is processed to reflect the time spent processing the datagram.
Even if no local information is available on the time actually
spent, the field must be decremented by 1. The time is measured in
units of seconds (i.e. the value 1 means one second). Thus, the
maximum time to live is 255 seconds or 4.25 minutes. Since every
module that processes a datagram must decrease the TTL by at least
one even if it process the datagram in less than a second, the TTL
must be thought of only as an upper bound on the time a datagram may
exist. The intention is to cause undeliverable datagrams to be
discarded, and to bound the maximum datagram lifetime.
Some higher level reliable connection protocols are based on
assumptions that old duplicate datagrams will not arrive after a
certain time elapses. The TTL is a way for such protocols to have
an assurance that their assumption is met.
On page 27, it discusses fragment reassembly:
...
If this is the first fragment (that is the fragment offset is
zero) this header is placed in the header buffer. If this is the
last fragment ( that is the more fragments field is zero) the
total data length is computed. If this fragment completes the
datagram (tested by checking the bits set in the fragment block
table), then the datagram is sent to the next step in datagram
processing; otherwise the timer is set to the maximum of the
current timer value and the value of the time to live field from
this fragment; and the reassembly routine gives up control. ...
And the glossary defines the TTL quite succinctly (page 43):
Time to Live
An internet header field which indicates the upper bound on
how long this internet datagram may exist.
The only thing I've found that contradicts my position is this (again from page 30):
This field must be decreased at each point that the internet header is processed to reflect the time spent processing the datagram.
However, this is not exclusive, i.e. it doesn't say that the field must only be decreased to reflect the processing time, and interpreting it as being exclusive would contradict the other sections that I have quoted.
There is a reason why acronyms like "IIRC" and "AFAIK" exist. If you can't be bothered to research things (which is understandable; this is Slashdot, after all) then you should at least have the honesty to use those acronyms.
Of course, ping is ICMP not TCP and thus is not subject to this problem.
Actually, the IPv4 packet will expire long before the maximum TCP RTT comes into effect. From RFC 791, section 3.1; page 14 (with emphasis added):
Time to Live: 8 bits
This field indicates the maximum time the datagram is allowed to
remain in the internet system. If this field contains the value
zero, then the datagram must be destroyed. This field is modified
in internet header processing. The time is measured in units of
seconds, but since every module that processes a datagram must
decrease the TTL by at least one even if it process the datagram in
less than a second, the TTL must be thought of only as an upper
bound on the time a datagram may exist. The intention is to cause
undeliverable datagrams to be discarded, and to bound the maximum
datagram lifetime.
So, the maximum lifetime for an IPv4 packet is 255 seconds. That gives you a 510-second maximum ping time for IPv4.
IPv6 changed the field to be a pure "hop count", so perhaps you'll be able to use it to ping Voyager 1.
Of course, since Voyager 1 had set pushlatency -100000, it got a good 26 hours of fun fragging you all before it finally got the message that it had been kicked and its frags didn't count.
The same reason why Dan Bernstein used the 1955 RAND tables to generate a constant for a public-key signature system he designed: It's very unlikely that somebody 20+ years ago, with the technology that was available 20+ years ago, would be able to craft a Thompson hack that would successfully insert a backdoor into something like gcc 4.0, which hadn't even been imagined at the time.
Of course, if you don't already have an old Tandy machine, and you instead try to acquire one from eBay, you won't really know that it hasn't been modified more recently.
All you need to do, in that case, is write a C interpreter in assembler that can interpret enough of the C language to run the compiler interpretatively as it compiles the compiler.
But how do you know that your assembler isn't compromised? Or your text editor? Or the operating system they run on? Or the BIOS?
For reference, the actual algorithm is LZW (Lempel-Ziv-Welch), not LZH. LZH is compressed file format (similar in function to ZIP) generated by old versions of LHarc.
I'm curious where you are from. I'm only curious because, dollars to doughnuts (ahhh, American Idioms), it's a country that has had periods of idiocy comparable to ours. Probably, if it is a nation of any decent age, a period of idiocy that undoubtedly makes ours seem in comparison puny and historically insignificant, sort of like a mental hiccough. Can you think of one that hasn't? Even Switzerland had Calvin.
If it doesn't exist, write it yourself! I recommend you get a copy of Applied Cryptography, and implement 3DES using inner-CBC mode. Oh, also be sure to use lots of ASN.1 encoding everywhere.
Meanwhile, high fees for Unix outraged Richard Stallman, a grad student who used it at the MIT artificial intelligence lab. Software, he decided, was an intellectual asset and should be free, like the published work of his fellow researchers. He set about building a set of tools called GNU that programmers could use to create their own software.
Sigh. High fees had nothing to do with it. Anyone who has spent an hour reading about the history of the GNU project would know that.
Oh, it's not that hard to see through your moral-equivalence bullshit.
Huh? I simply wrote that it wasn't discussed. But I guess you didn't bother to read my post either.
For the record, I certainly am not willing to make blanket statements that the military interventions of the USA were good or bad. Soviet-style "communism" was a significant threat to everything else, and even once the Soviet Union was dissolved, the military actions of the USA were largely consequences of previous meddling. IIRC, the US installed Saddam Hussein in Iraq, so was it appropriate for the US to remove him at a later date? It's difficult to say, and none of the options are particularly appealing.
But none of that is relevant to the simple statement that the US pissed a lot of people off, and so it's reasonable to expect that it will eventually experience some backlash as a result. It's a statement of fact, not morality.
Well, I don't agree that they're good suggestions, because I do have the knowledge to help with the Debian installer.
The Debian installer is designed to install Debian in the common case. It's not a rescue disc, nor is it a way to get Debian installed on weird configurations. If you need a diagnostics disc, use a live CD (there are ones besides Knoppix). If you need to install Debian on esoteric systems, then boot that live CD and use debootstrap.
grub is a fragile program (though less fragile than LILO). If grub is failing, you might have a broken BIOS. That's hardly Debian's fault (though with some effort, you might *still* be able to get Debian working on the machine).
In any case, my real point was that it's a volunteer-run effort, and ranting on Slashdot that those volunteers "should be the first ones against the wall" is completely unproductive.
There's a reason why it was removed in the first place. If . is in your path, the following commands can wipe out your system: "cd/home/someuser ; ls". The reason it could is that there could be a shell script called "/home/someuser/ls" that contains the command "/bin/rm -rf/". With . removed from your path, "ls" will always mean "ls".
In any case, I don't think the prevailing theory is that humans evolved from present-day apes, but that humans and apes (and chimpanzees... basically all primates) evolved from a common ancestor species.
Evolution isn't a scientific truth. It's a theory.
Your words are, strictly speaking, correct, but the thoughts that your words communicate to those who read them are not.
"Scientific truth" doesn't really exist. The closest thing that approaches that description is raw data that is collected by a well-run experiment.
There are these rocks (and sometimes rocks with DNA), that look a lot like animal skeletons and are located in specific places, but they don't look like the skeletons of any of the animals we currently find in those areas (or anywhere in the world). However, these rocks have similarities with each other and with present-day animals, and they were buried in places that suggest a particular age (according to theory). Those are the facts.
There are several theories of evolution. The first is the "Theory of Evolution"---the theory that evolution happens at all, and can explain the rocks and the DNA. This is virtually undisputed in the scientific community (I say "virtually", because anyone with who gets a Bachelor/Master of Science, from any school, is technically part of the "scientific community", so you'll always find someone who is willing to disagree.) There are also several other theories of evolution, that attempt to explain the detailed mechanism by which evolution occured and occurrs. Those are the theories that are disputed within the scientific community, and they often change when new data is uncovered (for a popular example, see Brontosaurus).
Similarly, there are several theories of gravity, which cover the specific mechanism by which gravity occurs, or which cover the precise strength of gravity in various extreme circumstances. There are probably even some people in the scientific community who dispute that gravity occurs at all. However, we probably shouldn't base social policy on claim that "gravity might not exist", or that "gravity is 'only' a theory".
The issue has taken on the sentiment that if the concept of evolution becomes widely accepted then faith is voided and we enter moral decay (which is obviously wrong, thanks Bush).
If that's the case, then it tells that most Americans are more likely to believe what they find desirable to believe, rather than the truth. That's a scary notion, when you consider that the USA has by far the largest military in the world, and that the overall actions of the USA are mostly driven by American public opinion.
Yep, the United States has done a hell of a lot of good in the world. Thanks for pointing it out in such detail.
Oh, such a smug answer! I bet you think you're really clever, don't you?
Re-read the post. mrraven wrote:
Really it's inevitable you kick someone in the balls and they want to strike back, that's just common sense and we have kicked a LOT of people in the balls in the last 60 years.
He never stated that said kicking of people in the balls was good or bad.
I love it when people who are unfamiliar with the law try to write legalese.
Think about it: Do you honestly think that if the military needs some technology, and it's available, that they won't use it because of copyright law? Especially if the design of the system in use is classified?
This proprietary software licence is not even going to accomplish its own goals.
Slashdot Mirror
As a Unix-like operating system user, I find it equally valuable: My Windows key opens xterm windows.
That might help, but it's not a complete solution, as anyone who has read Ken Thompson's Reflections on Trusting Trust knows.
Actually, it does. In several places. Search for "time to live" (case insensitive) in the RFC. You'll find that it is quite clear that the TTL is intended to be the maximum total datagram lifetime, so obviously a router will have to account for transmission delays.
For example, see page 30 (emphasis mine):
On page 27, it discusses fragment reassembly:
And the glossary defines the TTL quite succinctly (page 43):
The only thing I've found that contradicts my position is this (again from page 30):
However, this is not exclusive, i.e. it doesn't say that the field must only be decreased to reflect the processing time, and interpreting it as being exclusive would contradict the other sections that I have quoted.
There is a reason why acronyms like "IIRC" and "AFAIK" exist. If you can't be bothered to research things (which is understandable; this is Slashdot, after all) then you should at least have the honesty to use those acronyms.
Very awesome! Are you working there now?
Bigger than the alternatives that are just as easy if not easier to acquire.
But how young is too young to allow your children to use RTG-powered cellphones?
Actually, the IPv4 packet will expire long before the maximum TCP RTT comes into effect. From RFC 791, section 3.1; page 14 (with emphasis added):
So, the maximum lifetime for an IPv4 packet is 255 seconds. That gives you a 510-second maximum ping time for IPv4.
IPv6 changed the field to be a pure "hop count", so perhaps you'll be able to use it to ping Voyager 1.
Of course, since Voyager 1 had set pushlatency -100000, it got a good 26 hours of fun fragging you all before it finally got the message that it had been kicked and its frags didn't count.
The same reason why Dan Bernstein used the 1955 RAND tables to generate a constant for a public-key signature system he designed: It's very unlikely that somebody 20+ years ago, with the technology that was available 20+ years ago, would be able to craft a Thompson hack that would successfully insert a backdoor into something like gcc 4.0, which hadn't even been imagined at the time.
Of course, if you don't already have an old Tandy machine, and you instead try to acquire one from eBay, you won't really know that it hasn't been modified more recently.
But how do you know that your assembler isn't compromised? Or your text editor? Or the operating system they run on? Or the BIOS?
Finally, a use for those old Tandy machines!
For reference, the actual algorithm is LZW (Lempel-Ziv-Welch), not LZH. LZH is compressed file format (similar in function to ZIP) generated by old versions of LHarc.
No! My penis is bigger than yours!
How is that even an argument?
If it doesn't exist, write it yourself! I recommend you get a copy of Applied Cryptography, and implement 3DES using inner-CBC mode. Oh, also be sure to use lots of ASN.1 encoding everywhere.
Signed,
NOT The Government
From the article:
Sigh. High fees had nothing to do with it. Anyone who has spent an hour reading about the history of the GNU project would know that.
Huh? I simply wrote that it wasn't discussed. But I guess you didn't bother to read my post either.
For the record, I certainly am not willing to make blanket statements that the military interventions of the USA were good or bad. Soviet-style "communism" was a significant threat to everything else, and even once the Soviet Union was dissolved, the military actions of the USA were largely consequences of previous meddling. IIRC, the US installed Saddam Hussein in Iraq, so was it appropriate for the US to remove him at a later date? It's difficult to say, and none of the options are particularly appealing.
But none of that is relevant to the simple statement that the US pissed a lot of people off, and so it's reasonable to expect that it will eventually experience some backlash as a result. It's a statement of fact, not morality.
Well, I don't agree that they're good suggestions, because I do have the knowledge to help with the Debian installer.
The Debian installer is designed to install Debian in the common case. It's not a rescue disc, nor is it a way to get Debian installed on weird configurations. If you need a diagnostics disc, use a live CD (there are ones besides Knoppix). If you need to install Debian on esoteric systems, then boot that live CD and use debootstrap.
grub is a fragile program (though less fragile than LILO). If grub is failing, you might have a broken BIOS. That's hardly Debian's fault (though with some effort, you might *still* be able to get Debian working on the machine).
In any case, my real point was that it's a volunteer-run effort, and ranting on Slashdot that those volunteers "should be the first ones against the wall" is completely unproductive.
There's a reason why it was removed in the first place. If . is in your path, the following commands can wipe out your system: "cd /home/someuser ; ls". The reason it could is that there could be a shell script called "/home/someuser/ls" that contains the command "/bin/rm -rf /". With . removed from your path, "ls" will always mean "ls".
Otherwise, you have a point.
In any case, I don't think the prevailing theory is that humans evolved from present-day apes, but that humans and apes (and chimpanzees... basically all primates) evolved from a common ancestor species.
Your words are, strictly speaking, correct, but the thoughts that your words communicate to those who read them are not.
"Scientific truth" doesn't really exist. The closest thing that approaches that description is raw data that is collected by a well-run experiment.
There are these rocks (and sometimes rocks with DNA), that look a lot like animal skeletons and are located in specific places, but they don't look like the skeletons of any of the animals we currently find in those areas (or anywhere in the world). However, these rocks have similarities with each other and with present-day animals, and they were buried in places that suggest a particular age (according to theory). Those are the facts.
There are several theories of evolution. The first is the "Theory of Evolution"---the theory that evolution happens at all, and can explain the rocks and the DNA. This is virtually undisputed in the scientific community (I say "virtually", because anyone with who gets a Bachelor/Master of Science, from any school, is technically part of the "scientific community", so you'll always find someone who is willing to disagree.) There are also several other theories of evolution, that attempt to explain the detailed mechanism by which evolution occured and occurrs. Those are the theories that are disputed within the scientific community, and they often change when new data is uncovered (for a popular example, see Brontosaurus ).
Similarly, there are several theories of gravity, which cover the specific mechanism by which gravity occurs, or which cover the precise strength of gravity in various extreme circumstances. There are probably even some people in the scientific community who dispute that gravity occurs at all. However, we probably shouldn't base social policy on claim that "gravity might not exist", or that "gravity is 'only' a theory".
Nice troll; Well done.
If that's the case, then it tells that most Americans are more likely to believe what they find desirable to believe, rather than the truth. That's a scary notion, when you consider that the USA has by far the largest military in the world, and that the overall actions of the USA are mostly driven by American public opinion.
Oh, such a smug answer! I bet you think you're really clever, don't you?
Re-read the post. mrraven wrote:
He never stated that said kicking of people in the balls was good or bad.
I love it when people who are unfamiliar with the law try to write legalese.
Think about it: Do you honestly think that if the military needs some technology, and it's available, that they won't use it because of copyright law? Especially if the design of the system in use is classified?
This proprietary software licence is not even going to accomplish its own goals.
How come Slashdot is only listed once?
It was ABOUT Slashdot, not ON Slashdot. otherwise there would have been the obligatory dupe, listing them twice.
Google just took over the Deja News database.
Call a Java module? You mean, like, another language? That's dirty and evil. We write all our code in rock-solid PHP 4.
-- The Management