4 ms·

DNS label name limit is 63 characters, and total length limit 255 (or thereabouts). Maybe newer implementations allow longer names, you'd have to test though.

DNS label name limit is 63 characters, and total length limit 255 (or thereabouts). Maybe newer implementations allow longer names, you'd have to test though. https://stackoverflow.com/questions/32290167/what-is-the-maximum-length-of-a-dns-name https://stackoverflow.com/questions/32290167/what-is-the-max...

mytailorisrich 6y ago
> and total length limit 255 (or thereabouts) The continuous discussion about "thereabouts" is because the 255 bytes limit applies to encoded name fields (in DNS messages), not domain names as we usually write them in dotted format. Since the encoded format is that each label is preceded by its length and the whole domain ends by 'root' (i.e. 0x00) this means that domains names as we usually write them are limited to 253 bytes, including the dots (we don't write the 'root' label and label lengths are replaced by dots except the first one, that's 2 bytes to subtract from 255).
123048713 6y ago
You can have a lot more fun than that if you want to break things. An IP address has lots of valid formats nobody uses. ;; ANSWER SECTION: wikipedia.org. 599 IN A 208.80.154.224 Lets try this in decimal: http://3494943456/ http://3494943456/ Sort of cool, but what happens if we overflow it by adding 232? >>> 3494943456 + 2**32 http://7789910752/ http://7789910752/ I mean that's cool, but how far can we go? >>> 3494943456 + (2**32) ** 2 http://18446744077204495072/ http://18446744077204495072/ So that still works, what about going further? >>> 3494943456 + (2**32) ** 100 http://1976906478982563993654226439837963340315390682625773828918265710158340601093951126756295848974613063099294244703164628428967968057547050608904859234600159014229329102195101574081057061661948106884800321129818693914608845281661462333814326544389741164009367602548103882724187831587394954463183137735657307019637359169290834318700453890617892714561362370427388384101316010134426924662084888461376218489653794242999053891151382465888482003300085676110173467997003494159830094271947506024974271953414706038068210170338961663202839203641120865263292248718692924915189291455200665479606951612257868495299167071771306894428954788679149900427954823300393640007649397742106635573828425752730305375232721339803871889299281134208211131341001135605446809477409979279627213188610112867929569789492640465736633925065052540962862027736312499143902692033755536952046162410311395501619568814547777271031259247973250866583116853615908352881305587297178183145388745781297005733124832/ http://19769064789825639936542264398379633403153906826257738... Going further actually breaks some browsers (Firefox can handle longer than Internet Explorer for example), breaks web servers because they log the full version before it is transformed, and even acts as a fingerprinting vector. The limit is usually in the several hundred kilobyte range, and depending on the way that the underlying operating system handles it, things get seriously broken very quickly.
- ComputerGuru 6y ago
  Interestingly, Safari on iOS only works with the first link you posted. From the first overflow it displays an invalid URL error. You should probably include the OS+browser combo you used, as it does not seem to be universal.
  - chipsa 6y ago
    First and last work for me on mobile Safari, but not the middle two.
- jerf 6y ago
  In Firefox, when I hover over http://3494943456/ http://3494943456/ it displays as http://208.80.154.224 http://208.80.154.224 in the lower left, as does 1844... and 197690..., BUT http://7789910752/ http://7789910752/ displays as exactly that string. It likewise navigates to the first, third, and fourth links but breaks on your second.
- c22 6y ago
  Way back in high school I used to use decimal ip addresses to bypass the network content filter. It doesn't work as well these days as so many sites are virtual hosted.

mytailorisrich 6y ago

> and total length limit 255 (or thereabouts) The continuous discussion about "thereabouts" is because the 255 bytes limit applies to encoded name fields (in DNS messages), not domain names as we usually write them in dotted format. Since the encoded format is that each label is preceded by its length and the whole domain ends by 'root' (i.e. 0x00) this means that domains names as we usually write them are limited to 253 bytes, including the dots (we don't write the 'root' label and label lengths are replaced by dots except the first one, that's 2 bytes to subtract from 255).

123048713 6y ago

You can have a lot more fun than that if you want to break things. An IP address has lots of valid formats nobody uses. ;; ANSWER SECTION: wikipedia.org. 599 IN A 208.80.154.224 Lets try this in decimal: http://3494943456/ http://3494943456/ Sort of cool, but what happens if we overflow it by adding 232? >>> 3494943456 + 2**32 http://7789910752/ http://7789910752/ I mean that's cool, but how far can we go? >>> 3494943456 + (2**32) ** 2 http://18446744077204495072/ http://18446744077204495072/ So that still works, what about going further? >>> 3494943456 + (2**32) ** 100 http://1976906478982563993654226439837963340315390682625773828918265710158340601093951126756295848974613063099294244703164628428967968057547050608904859234600159014229329102195101574081057061661948106884800321129818693914608845281661462333814326544389741164009367602548103882724187831587394954463183137735657307019637359169290834318700453890617892714561362370427388384101316010134426924662084888461376218489653794242999053891151382465888482003300085676110173467997003494159830094271947506024974271953414706038068210170338961663202839203641120865263292248718692924915189291455200665479606951612257868495299167071771306894428954788679149900427954823300393640007649397742106635573828425752730305375232721339803871889299281134208211131341001135605446809477409979279627213188610112867929569789492640465736633925065052540962862027736312499143902692033755536952046162410311395501619568814547777271031259247973250866583116853615908352881305587297178183145388745781297005733124832/ http://19769064789825639936542264398379633403153906826257738... Going further actually breaks some browsers (Firefox can handle longer than Internet Explorer for example), breaks web servers because they log the full version before it is transformed, and even acts as a fingerprinting vector. The limit is usually in the several hundred kilobyte range, and depending on the way that the underlying operating system handles it, things get seriously broken very quickly.

ComputerGuru 6y ago
Interestingly, Safari on iOS only works with the first link you posted. From the first overflow it displays an invalid URL error. You should probably include the OS+browser combo you used, as it does not seem to be universal.
- chipsa 6y ago
  First and last work for me on mobile Safari, but not the middle two.
jerf 6y ago
In Firefox, when I hover over http://3494943456/ http://3494943456/ it displays as http://208.80.154.224 http://208.80.154.224 in the lower left, as does 1844... and 197690..., BUT http://7789910752/ http://7789910752/ displays as exactly that string. It likewise navigates to the first, third, and fourth links but breaks on your second.
c22 6y ago
Way back in high school I used to use decimal ip addresses to bypass the network content filter. It doesn't work as well these days as so many sites are virtual hosted.