finding-ac-mtu.sh

# since Ubuntu still cannot find proper MTU with MTU=automatic. it gets set too low and causes connection problems. 
# Hear is how to find MTU used on the current net by your AP:

# 1. Set up high (unrealistic) value, eg, 2000:
sudo ifconfig  wlan0 mtu 2000

# 2. Ping a few times a well know host (suppressing fragmentation - Don't Fragment (DF)) with 
# different packet sizes starting with.
# Either "any device along the path whose MTU is smaller than the packet will drop it, and send back an 
# Internet Control Message Protocol (ICMP) Fragmentation Needed (Type 3, Code 4) message containing its MTU". Then you
# can use the given MTU. Or it fails and you need to reduce packet size till it gets through. Subtrackt 28 from the
# packet size and use it as your MTU.

ping -M do -s 1473 www.google.com

#> PING www.google.com (119.224.142.53) 1473(1501) bytes of data.
#> From NF4V.Home (192.168.20.1) icmp_seq=1 Frag needed and DF set (mtu = 1500)
#> ping: local error: Message too long, mtu=1500

# MTU=1500

# More reading:
# https://en.wikipedia.org/wiki/Path_MTU_Discovery
# http://muzso.hu/2009/05/17/how-to-determine-the-proper-mtu-size-with-icmp-pings