ssh-config

Host *
    ForwardAgent yes
    ProxyCommand ~/bin/ssh-proxy.sh %h %p username@jump-host
    ServerAliveInterval 10
    ServerAliveCountMax 600

ssh-proxy.sh

#!/bin/bash

# ------------------------------------------------------------------------------
# Use SOCKS proxy to proxy SSH through a jump host.  This works in
# almost all circumstances and has the advantage of using only one
# SSH tunnel to the jump host for all concurrent ssh tunnels.  It
# does not end the open connection to the jump host when the connection
# is closed.
# ------------------------------------------------------------------------------
# Author: Karl Matthias
# Date:   Tue 31 Jan 2012

hostname=$1
port=$2
proxy_host=$3

usage() {
  die "`basename $0`: [hostname] [port] [proxy_host]"
}

die() {
  echo $1 >&2
  exit 1
}

test -z $hostname && usage
test -z $port && usage
test -z $proxy_host && usage

nc -z -w 2 $hostname $port > /dev/null 2>&1
if [[ $? -eq 0 ]]; then
  nc -w 300000 $hostname $port
else
  nc -z -w 2 localhost 9090 > /dev/null 2>&1
  if [[ $? -ne 0 ]]; then
    ssh -f -N -D9090 $proxy_host
  fi

  nc -x localhost:9090 $hostname $port
fi