ssh bug with cisco - Putty works, but Linux ssh doesn't.

 ssh -v freeze with line:

 debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP

Edit for fix  /etc/sysctl.conf

# fix bug with cisco vpn
net.ipv4.tcp_mtu_probing = 2

and reload config

sudo sysctl -p /etc/sysctl.conf