<whitequark>
balrog: then you should find your network administrator and give him a kick in the ass
<azonenberg_hk>
balrog: this is one of many reasons icmp should not be turned off :p
<azonenberg_hk>
among other things, it means networks with weird mtus fail silently
<azonenberg_hk>
vs sending smaller tcp segments
<balrog>
azonenberg_hk: our security group likes to turn off ICMP because apparently having it on prevents them from using acceleration in their firewall appliance
<azonenberg_hk>
wuuut
<balrog>
or rather block it in the firewall
<azonenberg_hk>
i have had lots of corp networks block OUTBOUND ping requests
<azonenberg_hk>
no idea why
<balrog>
I'm not sure if they're blocking all ICMP though or just pink
<balrog>
ping*
<azonenberg_hk>
And i once had a bug where certain websites wouldnt load at my parents
<whitequark>
"certain websites won't load" instantly screams "MTU" at me
<azonenberg_hk>
whitequark: yes, it does now
<azonenberg_hk>
not then :p
<whitequark>
loll
<azonenberg_hk>
Anyway, yeah
<azonenberg_hk>
1500 byte MTU
<azonenberg_hk>
PPPoE header meant actual link MTU was 1492
<azonenberg_hk>
(ADSL)
<whitequark>
I had no doubt whatsoever it was PPPoE
<azonenberg_hk>
So any time a website sent a packet in the 1493-1500 byte size range it never made it
<balrog>
ADSL is generally PPPoE
<azonenberg_hk>
balrog: yeah well, this was my first time setting up ADSL
<balrog>
so what's the solution?
<azonenberg_hk>
this was years ago
<balrog>
ahhh
<azonenberg_hk>
balrog: Have the router advertise a 1492 byte link MTU
<balrog>
oh, so it was lying?
<balrog>
or did someone change it to "increase performance"?
<qu1j0t3>
azonenberg_hk: +1, that's what i recall from my first ADSL setup
<whitequark>
I think the way I solved is by using -j TCPMSS --clamp-mss-to-pmtu
<azonenberg_hk>
ip tcp adjust-mss
<azonenberg_hk>
it was a cisco
<whitequark>
so this handles the case where..
<whitequark>
the sender thinks that link MTU is 1500 because it's connected to ethernet
<azonenberg_hk>
i think it just patches the tcp header in an outbound SYN to negotiate a slightly smaller MTU
<whitequark>
something between the sender and the receiver drops th ICMP Size Exceeded packets
<azonenberg_hk>
Yes
<azonenberg_hk>
this is exactly what happened
<whitequark>
then you have to hack the TCP packets to artificially restrict MSS
<azonenberg_hk>
And packets in the 1493-1500 byte size range died
<azonenberg_hk>
Correct
<whitequark>
because the sender has no idea it has to do it
<azonenberg_hk>
So i did it on the router
<azonenberg_hk>
one line config change, problem solved
<azonenberg_hk>
whitequark: "some websites didnt load" screamed DNS problem to me initially
<whitequark>
qu1j0t3: are you @crzwdjk by any chance
<azonenberg_hk>
i spent way too much time barking up the wrong tree
<lain>
fragmentation can do weird things to firewalls if the admins are too lazy or the firewalls are too stupid to deal with it
<whitequark>
screw fragmentation
<azonenberg_hk>
Fragmentation means you set the MTU wrong
<azonenberg_hk>
Fix your MTU and drop all frags
<whitequark>
... with TCP
<azonenberg_hk>
UDP packets rarely if ever have to be bigger than a sane MTU
<whitequark>
with UDP not so much
<azonenberg_hk>
most protocols over udp are designed to cap max packet size for this exact reason
<azonenberg_hk>
with TCP its easy to patch the mss
<whitequark>
yeah
<whitequark>
>When IPv6 is used as the network protcol, the MSS is calculated as the maximum packet size minus 60 bytes. An MSS of 65535 should be interpreted as infinity.
<whitequark>
>infinity
<whitequark>
really?
<whitequark>
infinity?
<whitequark>
this is the value you suggest?
* lain
dies
<azonenberg_hk>
whitequark: fwiw thats a SHOULD
<qu1j0t3>
>.<
<azonenberg_hk>
so at least you have the option of being smaller :p
<whitequark>
lol
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<rqou>
whitequark: i tried contacting the electrolab people about whether i need to arrange a visit and i got no replies
<rqou>
do i just show up during their listed hours of 1400-1900?
<whitequark>
yes
<rqou>
unfortunately their website is basically 100% french
<nats`>
rqou, yep
<rqou>
anyways, we're leaving for france tomorrow
<nats`>
they are pretty cool
<rqou>
nats` are you in the paris area?
<rqou>
meetup?
<nats`>
I'm but not at the moment unfortunately
<nats`>
:|
<nats`>
where do yo ucome from ?
<rqou>
i am currently in london
<nats`>
I may travel to Silverstone in a near future
<rqou>
from california USA originally
<nats`>
ahhhh never went to USA
<nats`>
:)
<rqou>
anyways, being a "stupid american" in paris is going to be fun :P
<nats`>
paris is not a complicated city
<nats`>
but electrolab is not directly in paris
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<nats`>
it's the north west
<whitequark>
nanterre is not very hard to find
<whitequark>
there's a train stop nearby
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<nats`>
yep
<rqou>
so how does public transit work in Paris?
<whitequark>
rqou: you buy a paper ticket
<rqou>
is there a transit card I can get?
<whitequark>
need to select depart/arrival station at the vending machine
<nats`>
how long do you stay here ?
<whitequark>
not sure about transit cards, I was only for 3 days in fr
<rqou>
3 days, then heading into Germany
<nats`>
and you'll move a lot ?
<nats`>
where is your hotel ?
<rqou>
not sure, no real plan yet
<rqou>
hotel is grand hotel saint michel
<nats`>
ah cool directly in the center :)
<rqou>
nats` what do you recommend we see or do?
<nats`>
the electrolab is cool, there is the tmplab too
<nats`>
if you never came here you have to see ;but not necessarily visit it, eiffel tower
<nats`>
the Musee d'orsay and Louvre are must see too :)
<nats`>
if you like modern art, beaubourg is cool :)
<nats`>
it's not a legend there are so much things to do in paris