Hello, I want to understand where the adrr 172.16.238.10 / 172.16.239.10 are coming from, how did we know this information? Why these addr act as gateways for jump host? I dont recall assigning these addr in previous questions 
Thanks !
Let’s look at the IP addresses separately. 172.16.238.10 was assigned to eth0 on jump_host via the lab setup software; you didn’t set up, but it was set up from the start. From ip addr on jump_host:
11: eth0@if12: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 02:42:ac:10:ee:0a brd ff:ff:ff:ff:ff:ff link-netnsid 0
inet 172.16.238.10/24 brd 172.16.238.255 scope global eth0
valid_lft forever preferred_lft forever
This puts us on the same network as app01 and app02. But we need access to app03 and app04, which are on a separate network (172.16.239.0/24). So we create a new IP address on an interface that has access to that other network. It turns out that we can use eth0 for this, so we create the IP address using:
sudo ip addr add 172.16.239.10/24 dev eth0
Once we do that, we can route to all 4 appXX hosts:
hor@jump_host ~$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default gateway 0.0.0.0 UG 0 0 0 eth0
172.16.238.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
172.16.239.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
172.17.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1
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A diagram always helps. In this we can clearly see that jump_host has 2 interfaces, one connected to each network. Therefore to route from AppServer1 to Appserver 3 or 4, you must go via jump_host
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Got it, Thank you 