ssh -t shmem@gateway ssh -t admin@host.example.com \
  ssh -t wrxd15@192.168.123.2 ssh -t root@192.168.254.2

##</code><code>##

              host1      host2      host3
            +-------+  +-------+  +-------+
ssh 1 ----------\   |  |       |  |       |
ssh 2 ---------------------\   |  |       |
ssh 3 ================================>   |
ssh 2 ---------------------/   |  |       |
ssh 1 ----------/   |  |       |  |       |
            +-------+  +-------+  +-------+

##</code><code>##

              host1      host2      host3
            +-------+  +-------+  +-------+
            |       |  |       |  |       |  
            |       |  |       |  |       |  
ssh 1 ======> ssh 2 ===> ssh 3 =======>   |
            |       |  |       |  |       |  
            |       |  |       |  |       |  
            +-------+  +-------+  +-------+

##</code><code>##

              host1      host2      host3     | |
            +-------+  +-------+  +-------+   | |
ssh 1 ---------\    |  |       |  | proxy |   |n|
ssh 2 --------------------\    |  |   arp |   |e|
ssh 3 --------------------------------\  \|   |t|
ppp ===== compress ======================^===== |
ssh 3 --------------------------------/   |   |w|
ssh 2 --------------------/    |  |       |   |o|
ssh 1 ---------/    |  |       |  |       |   |r|
            +-------+  +-------+  +-------+   |k|