FSO Wifi - can ping but cannot download

Cesar Eduardo Barros cesarb at cesarb.net
Mon Aug 4 12:46:35 CEST 2008

Andy Green escreveu:
> Somebody in the thread at some point said:
> | I've configured WiFi on a fresh FSO image the same way I had on a 2008.2
> | image--by creating a wpa_supplicant.conf file and editing
> | /etc/network/interfaces.  This configuration worked on the 2008.2 image
> | but when I try implementing it on an FSO image, I cannot download
> | anything.  I can ping sites and when using wget, I can connect to them,
> | but downloading never commences.  It's not a DNS issue because ping and
> | wget seem to be able to resolve correctly.  Any thoughts?
> Sounds specific to tcp transport, ping is ICMP and DNS usually UDP.
> Maybe connect to a local Linux box and run tcpdump on there to study
> what it sees from the connection action.

No, it's not "ping and DNS do not use TCP". It's "ping and DNS and TCP 
SYN are small packets, data transfer is large packets", i.e. PMTU 
blackhole. I've seen that thing happen way too many times, and the 
workaround is almost always a MSS clamp (which is an ugly but 
unfortunately necessary hack).

Cesar Eduardo Barros
cesarb at cesarb.net
cesar.barros at gmail.com

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