IP Routing Simulation

• Gil Messerman
• Gilad Karni
• Uri Braun

Questions: How do I...

• Add a network
• Add a host to a network
• Edit a network
• Define network's address pool
• Define network's MTU
• Set network's default gateway
• Connect a network to a router \ Disconnect a network from a router
• Remove a network

• Add a router
• Edit a router
• Connect a router to a network \ Disconnect a router from a network
• Remove a router

• Add a host to a network
• Remove a host

• Add a datagram
• Edit a datagram
• Set a datagram's source & target hosts
• Set a datagram's source host
• Set a datagram's target host
• Set a datagram's length
• Set a datagram's TTL
• Send a datagram
• Remove a datagram

• What is the purpose of "Place Networks"?
• Why can't I add a host to a network?
• How can I remove all objects from main panel?
• Why can't I send a datagram?
• How does a host get its IP address?

Answers: How do you...

• Add a network
  Back to: Top | Questions | Network



Right clicking on the main panel will cause a menu to pop up.
Choose "Add Network" and a new network will show up on the main panel.



• Add a host to a network
  Back to: Top | Questions | Network

Right clicking on the network will cause a menu to pop up.
Choose "Add Host" and a host will be added to the network.


FAQ - "Add Host" is disabled. Why can't I add a host to a network?
FAQ - How does a host gets its IP address?


• Edit a network
  Back to: Top | Questions | Network


• Define network's address pool
  Back to: Top | Questions | Network

Right click on the network you want to edit.
A menu will pop up. Choose "Edit Network" and a window with the network properties will be opened.

You can also double-click on the network in order to open the same window.

In that window you can define the network's address pool (Class based or CIDR based).


After defining a network's address pool the network's address
pool will appear on the network's icon:



• Define network's MTU
  Back to: Top | Questions | Network

Right click on the network you want to edit.
A menu will pop up. Choose "Edit Network" and a window with the network properties will be opened.

You can also double-click on the network in order to open the same window.

In that window you can define the network's MTU.




• Set network's default gateway
  Back to: Top | Questions | Network

When connecting a network to a router for the first time,
the router is automatically set to be the network's default gateway.

The default gateway of a network is denoted with a "d" on the line
connecting the network and the default gateway.



However, if your network is connected to more than one router and you
want to change the default gateway of network, you need to perform
a right click on the selected network and choose "Set Default Gateway"
on the menu that will pop up.


A bar indicating you are now choosing the default gateway will appear at the head of the main panel.


Then, all possible default gateways will be marked with a blue rectangle.
You can choose any of them to be the default gateway of the network.
The Chosen default gateway will be marked with a green rectangle.


When you're done choosing the default gateway, click the button "Done" at the bar at the head of the panel.
The default gateway will be set.

Read more about removing default gateways here.


• Connect a network to a router \ Disconnect a network from a router
  Back to: Top | Questions | Network

Click Here


• Remove a network
  Back to: Top | Questions | Network

Right clicking on a network will cause a menu to pop up.
Choose "Remove Network".


The network will be removed from the main panel along with its hosts.

• Add a router
  Back to: Top | Questions | Router

Right clicking on the main panel will cause a menu to pop up.
Choose "Add Router" and a new router will show up on the main panel.



• Edit a router
  Back to: Top | Questions | Router


Right clicking on the router will cause a menu to pop up.
Choose "Edit Routing Table".



This will cause an opening of a new window:


This window allows the user to define a routing table for the selected router.
The structure of a routing table is a list of lines where each line contains 4 elements:


Network destination	Used to define destination network. This value is compared with part of datagram's target IP address according to Netmask value. The network destination value might be either IP address of one of the defined networks or an address that aggregates several networks (supernet). For example in order to route a datagram to either network 192.168.10.0 or 192.168.11.0 using same Interface of selected router, the user may define network destination to be 192.168.0.0 with appropriate Netmask (255.255.0.0).
Netmask	Used to differ the prefix of datagram's target IP, which should be compared with the current entry's Network destination value.
Next hop	Used to define a router to which a datagram will be forwarded from current router in case Network Destination matches to defined prefix of datagram's target IP address. Two different cases of selection are available for this field: In case the datagram's destination network is not one of the networks that selected router is connected to, the user should select the next hop to be a router's IP address that will handle this datagram further. In case the router is connected directly to datagram's destination network, then the user should select the IP address of the selected router (on this network). In other words, in case the value of this field is an address of the selected router itself, the system will attempt to send the datagram directly to the target host.
Interface	Used to select router's network connection to which datagram will be forwarded if this routing table entry will match the datagram's target IP address.


In addition, to the right of each line, there is a "Remove" button that, when pressed, deletes the appropriate line from the table.

To add a new empty line to routing table the user should click "Add new line" button. The empty line will appear
and it must be properly configured, before saving the table or moving to another line in routing table.

In order to create basic routing table, which will be based on current configuration, the user may click, "Add entries for
each interface" button. This will add a line for each connected network, which configures the ability to
forward datagrams directly to hosts that are connected to selected router's network.

In order to create a default routing entry in routing table (to indicate where to forward a datagram that does not
match any of other entries) the user may click "Add default entry" button. This will add a line where
network destination and netmask will match to any datagram and all user has to do is to configure where the datagram
should be forwarded.


• Connect a router to networks \ Disconnect a router from networks
  Back to: Top | Questions | Router

Right clicking on the router will cause a menu to pop up.
Choose "Connect to Networks".


A bar will show up in the head of the applet indicating you are now connecting the router to a network.


A click on a network will mark it with a green rectangle.
Another click will unmark the green rectangle.
The green rectangle indicates that the router is connected to the
network.


When you finish connecting \ disconnecting, click the button "Done" at the bar at the head of the panel.
The connections you chose to make will be performed.



• Remove a router
  Back to: Top | Questions | Router

Right clicking on a router will cause a menu to pop up.
Choose "Remove Router".


The router will be removed from the main panel.

If you'll choose to remove a router that is happen to be a default gateway
of a certain network, three cases are possible:
1. The network is not connected to other routers besides the default gateway:
   In this case, a message notifying that the default gateway has been removed
   will be presented on the screen.
2. There's exactly one more router connected to the network besides the default gateway:
   In this case, the other router will be automatically set to be the default gateway.
3. The network is connected to more than one router besides the default gateway:
   In this case, the user will have the option to choose the default gateway of the network.

• Add a host to a network
  Back to: Top | Questions | Host

Right clicking on a network will cause a menu to pop up.
Choose "Add Host" and a host will be added to the network.


FAQ - "Add Host" is disabled. Why can't I add a host to a network?
FAQ - How does a host gets its IP address?


• Remove a host
  Back to: Top | Questions | Host

Right clicking on a host will cause a menu to pop up.
Choose "Remove Host". The host will be removed from the main panel.

• Add a datagram
  Back to: Top | Questions | Datagram

Right clicking on the main panel will cause a menu to pop up.
Choose "Add Datagram" and a new datagram will show up on the main panel.



• Edit a datagram
  Back to: Top | Questions | Datagram


• Set a datagram's source & target hosts

Right clicking on a datagram will cause a menu to pop up.
Choose "Set Source & Target".


A bar saying you now have to select the source host will appear
at the head of the panel.


You can, obviously, select only one source.
Select the source host by clicking it.
A successful selection will result in marking the host with a green rectangle.


When finishing selecting the source host, click "Done" at the bar at the head of the panel.
The bar will then instruct you to select the target host.


Repeat the process above for the target host.


• Set a datagram's source host
  Back to: Top | Questions | Datagram

Right clicking on a datagram will cause a menu to pop up.
Choose "Set Source Only".


A bar saying you now have to select the source host will appear
at the head of the panel.


You can, obviously, select only one source.
Select the source host by clicking it.
A successful selection will result in marking the host with a green rectangle.


When finishing selecting the source host, click "Done" at the bar at the head of the panel.


• Set a datagram's target host
  Back to: Top | Questions | Datagram

Right clicking on a datagram will cause a menu to pop up.
Choose "Set Target Only".


A bar saying you now have to select the target host will appear
at the head of the panel.


You can, obviously, select only one target.
Select the target host by clicking it.
A successful selection will result in marking the host with a green rectangle.


When finishing selecting the target host, click "Done" at the bar at the head of the panel.


• Set a datagram's length
  Back to: Top | Questions | Datagram

Right clicking on a datagram will cause a menu to pop up.
Choose "Edit Datagram". A window with the datagram properties will be opened.


Double-clicking on a datagram will also open the same window.

In that window you can select the datagram's length at the appropriate field.



• Set a datagram's TTL
  Back to: Top | Questions | Datagram

Right clicking on a datagram will cause a menu to pop up.
Choose "Edit Datagram". A window with the datagram properties will be opened.


Double-clicking on a datagram will also open the same window.

In that window you can select the datagram's TTL at the appropriate field.



• Send a datagram
  Back to: Top | Questions | Datagram

Right clicking on a datagram will cause a menu to pop up.
Choose "Send Datagram" and the datagram will be sent.


While sending a datagram a bar appears at the head of the main panel.
This bar gives information concerning the datagram traveling through the network.


The "Stop Simulation" button will stop the simulation a short time after pressing it.

When arriving a network, the bar will show the network's MTU:


When arriving a router, the bar will show the entry in the router routing table that was chosen:


The bar is also used for error reporting in the sending process.
For example:


And more...

Datagram Fragmentation
In case the datagram has to be fragmented, the datagram icon will be changed from     to  .
Also, the number of fragments will be shown in the brackets, next to the fragmented datagram icon:


More information concerning the number of fragments, and the length of each fragment can be found
in the bar at the head of the main panel:


FAQ - "Send Datagram" is disabled. Why can't I send my datagram?


• Remove a datagram
  Back to: Top | Questions | Datagram

Right clicking on a datagram will cause a menu to pop up.
Choose "Remove Datagram". The datagram will be removed from the main panel.

• What is the purpose of "Place Networks"?
  Back to: Top | Questions | FAQ

"Place Networks" menu item allows you to use predefined networks.
These networks are built-in in the applet.
After placing them on the panel, you may edit them as you like.


Three networks are available in the "Place Networks" menu:


1. Star - This network is constructed of three main networks connected using
   a router to each other. Each of these main networks is connected to another two
   "sub-networks".
   Hosts are allocated only in the "sub-networks".
   All routers are already configured to transfer datagrams between the hosts.
   Determine datagram's source and target, and send it.
   
   
2. Loop - This network simulates an error in the configuration of the routers.
   The source and the target of the datagram are already determined.
   Simply send the datagram and watch what happens.
   
   
3. Long - This network is constructed of a list of routers and networks.
   Routers are not configured.
   You may add networks, hosts, routers, datagrams and configure them as you like.
   
   
• Why can't I add a host to a network?
  Back to: Top | Questions | FAQ

First define an IP address for your network.
Then, you will be able to add hosts to your network.


• How can I remove all objects from main panel?
  Back to: Top | Questions | FAQ

A right click on the main panel will open a pop-up menu.
Select "Remove All" and the main panel will be cleaned of objects.



• Why can't I send a datagram?
  Back to: Top | Questions | FAQ

First define the datagram's source and target.
Then, you will be able to send the datagram.


• How does a host get its IP address?
  Back to: Top | Questions | FAQ

After the user has defined an IP address for a network, the network is responsible for allocating IP
addresses for any peripherals (hosts and routers) that are connected to it. The pool of addresses
is defined by network address. When creating a new host or connecting a router to the network, a free
address from the pool is allocated. When a host is being removed or a router is being disconnected
from a network, its IP address is deallocated and returned to pool.

Please note that allocation of addresses is not necessarily successive (e.g. for class C network
192.168.2.0 allocation of addresses for 2 hosts might return 192.168.2.1 and 192.168.2.3).