Lab # 3 Part 1- Experiments for the 5th Week

 

This lab covers the following Chapter in the text: 3.4.

Objectives

 

·        Static or Fixed Routing

 

Note: Understanding of IP routing prior to your laboratory session is essential for this week’s experiments.

Cisco has some useful info on their website on routing.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_c/ipcprt2/index.htm

1.1         Static Routing

 

Every routing decision is made by the routing table look-up. The routing table can be updated by a routing daemon (dynamic routing), ICMP redirect message, or the command that manipulates routing table entries (static routing).

 

A static route is one that you enter explicitly using commands. To build the routing table in your PC, the route command is used. Routing entries that are created manually don’t usually change, even if you run a routing daemon. Static routes are often added from the system startup script.

 

Routing table for PC

 

Your PC’s routing table can be displayed with the netstat command. We list the commands that are used to manually build the routing table in your PC.

 

netstat -rn : displays the routing table in the system.

route add -net destination_net_address netmask mask gw gateway_address: adds a new route to the routing table via a particular gateway, specifies the mask to be used for this entry. (-host will enter a host entry and one does not specify a netmask  for that.)

route del –net destination_net_address: deletes an existing route from the routing table

 

All the arguments are self-explanatory. For more details see the man pages.

 

Routing table for Router

 

You can manually configure the router’s table. In order to see the IP routing table in the router, in the privileged-level mode, type the following command:

 

            router_name# show ip route

 

The following commands are used to modify the routing table entries in the router. Type the following commands in the configuration mode. Read last lab’s “Configuring Router” section on how to get into the configuration mode.

 

ip route destination_address netmask router_address : creates a route to destination_address via router_address. The argument destination_address is the IP address of the target network, and the argument router_address is the address of a router that can reach destination_address . The mask gives the mask to be used for the destination address.

 

no ip route destination_address router_address : removes a route from the IP routing table.

1.1.1        A Single Router Experiment

For this experiment we will only be using a single router and two PCs connected via hubs to the router interfaces. Use the table below to set the IP addresses for the two PCs and the router. Note that because we are using a router, each interface has a different IP net address (compare to the bridge setup).

 


                       

 


Figure 3.1: Router experiment

 

 

router1

eth0

eth1

HOST_A

HOST_B

Name

IP Address

Name

IP Address

154.81.51.1

154.81.52.1

 

154.81.51.100

 

154.81.52.100

 

Table 3.1: IP addresses for Figure 3.1

 

Use setup from the console window to configure the router. If you disable bridging, ip routing is enabled. Do not enable any of the routing algorithms as we are using static routing and will be entering the routes manually! If you use the configure command instead to set up the router, you must enable routing by typing

 

ip routing

 

at the configure command.. As the router is directly connected to the only two subnets no manipulation of the router’s routing table is required at this point. Use the command:

 

show ip route

 

at the enable prompt to display the routing table.

Next you must setup the PC routing tables. As  they are both connected to an Ethernet to which only one router is attached, we can use the default entry to route all traffic not local to its subnet via the router. First check your PC routing tables using the netstat –rn or route commands. Then use the command:

 

route add –net 0 gw 154.81.51.1

 

on Host_A and the command:

 

route add –net default gw 154.81.52.1

 

on Host_B.

Now use the command netstat –rn or route on both PCs to check your routing tables. The “0” destination net address used in the command above reflects the default route (one can also type default). For default route you do not give any netmask. Note that the position of a routing entry indicates its search order. Whenever an IP device needs to route an IP datagram, it uses the routing table and searches thru it systematically starting with the first entry.

 

Exercise 1      

Run tethereal –V on your machine, and tethereal –V on the other machine in the other subnet at the same time. Send ping messages to the other machine. After receiving the tenth echo reply, quit the ping process and save the tethereal outputs for both machines.

 

Questions #1: 

·        When a packet is sent to a PC in the other subnet, explain how the source and destination Ethernet addresses are changed.

·        What are the source and destination addresses in the IP and Ethernet headers of a packet that goes from your machine to the router?

·        What are the source and destination addresses in the IP and Ethernet headers of a packet that goes from the router to the other machine?

·        Answer the same questions, but for the echo reply that is returned from the other machine.

·        Show the routing tables for both PCs.

 

Exercise 2:

Add to Host_A’s routing table the following entry:

 

route add –net 154.81.52.0 netmask 255.255.255.0 gw 154.81.51.1

 

Now check the routing table using netstat –rn or route (-e will give same output as netstat –rn and –ee will give everything!).

 

Questions #2:

1.1.2        A 4 Subnet Experiment

In this experiment, we divide the network into four subnets. There will be one machine in each of the following subnets, 154.81.51.0, 154.81.52.0, 154.81.53.0 and 154.81.54.0. As shown in figure 3.2, we will connect the four subnets (154.81.51.0, 154.81.52.0, 154.81.53.0, and 154.81.54.0) using three routers.

 

In order to configure the new network topology, we need to change the current IP addresses of each PC interface card. The new IP addresses that we want to use are as shown in the figure. (Note that 52.100 is an abbreviation for 154.81.52.100. This notation applies to all the PC and router addresses given in the figure above.)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 3.2: Topology for static routing

 

           

 

Exercise 3      

Change the IP addresses of the PCs to reflect the network configuration as shown in figure 3.1. Also configure the routers. Save the output of netstat -rn or route –ee before building the PCs’ routing tables. After examining figure 3.2, build the static routing table in all the PCs manually. Use netstat –rn or route –ee to verify your entries.

 

Save the routing tables of all the routers before building any routes. Note: You cannot telnet into the routers as they are on different subnets and the routing tables have not yet been entered. You need to use the console to configure each router.

 

Now configure the routing table in each router using the ip route command (e.g., ip route 154.81.51.0 255.255.255.0 154.81.52.1 will add the “51” subnet address to router 2’s table indicating that the router with port address 154.81.52.1 must be used as the next hop router). Note, as mentioned above, you must set ip routing. Recall that we set it to no ip routing to do bridging in last week’s experiment.

 

Use the ping and traceroute programs to test the connections. Save the traceroute outputs.

 

When you can reach other hosts successfully, save the routing tables of all the PCs and in the routers for the lab report. (Even if the routing table in your PC is correct and all the routers are configured perfectly, you may not get the connection to one of the other PCs. If this is the case, the routing table in the other PC should be blamed. When you can get the ping reply messages from all the interfaces in the PCs and routers successfully, your work is done for this exercise on static routing.)

 

Questions #3: 


Lab # 3 Part 2: Experiments for the 7th Week

 

This lab covers the following Chapters in the text: 3.4 and 5.1, 5.7, 5.8.

 

Objectives:

 

·        ICMP redirect error

·        Router Information Protocol (RIP)

·        Mixed Router – Bridge Experiment

 

Note: You may want to visit Cisco’s web site on IP routing: http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_c/ipcprt2/index.htm

 

1.2         Experiments with ICMP and Routing

 

Use the same network configuration as you did for the Static Routing experiment (Figure 3.2)

 

Exercise 4:

Empty the routing table of PC 154.81.52.100 by typing: route flush. Then add a default routing entry to gateway 154.81.51.1. Check the routing table by typing: netstat –rn. Save the contents. Run tethereal in a window on PC 154.81.52.100. Then ping from PC 154.81.52.100 to PC 154.81.53.100. Immediately after ping returns with “an alive” message check the routing table. Save the contents. Wait a few minutes then check the contents of the routing table again and save. Also save the tethereal output.

 

Questions #4:

1.3         Routing Information Protocol (RIP)

            Although there are many routing protocols, we will study one of the most common ones that is used for intra Autonomous System routing (Interior Gateway Protocols), the Routing Information Protocol (RIP). RIP is run by the routing daemon, routed, in your PC. The routing daemon dynamically builds the routing table from the received RIP updates. The PCs started routed at boot-up, no other action is needed to run RIP on the PCs. (Note: if you make any manual changes to the routing table (adds or deletes), routed will not touch manual changes. For example, if you accidentally delete an entry in the PC routing table, routed will not re-insert it. You have to kill the routed process (use: ps –ef  | grep routed to get the process ID, then kill process (process here refers to the process ID), and then restart it using: in.routed –q).

 

To enable a routing process for RIP on all interfaces in a router, use the following commands when in configuration mode. Refer to the “Configuring Router” section on how to get into configuration mode.

 

            router rip

            network network_number

 

network_number  is 154.81.0.0 for this network configuration.

 

To remove a network from the list:

 

            no network network_number

 

To shut down the routing process:

 

            no router rip

 

Note again that any routes that were added manually will not be updated by RIP.

 

 

Exercise 5

           

Empty all the routing tables in the PCs and the routers. Use Figure 3.2 again as the network configuration. Now start the RIP process in the routers.

 

After running RIP in all the routers, test the connections to the other hosts using either traceroute or ping. Once you can successfully reach all the hosts, save one of the RIP messages using tethereal –P udp -V in each subnet. Save the routing table in one of the PCs.

 

Questions #5: 

 

·        Draw the format of the saved RIP response packet from one of the subnets, include the IP and UDP headers and the RIP message (see Figure 5.11 in the textbook). Identify each field and express the numbers in decimal form.

·        Are the RIP packets propagated over the routers?

·        Show the contents of the routing table of one of the PCs after starting RIP.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 3.3: Rip Experiment

 

 

 

 

Exercise 6

           

Now connect the fourth router as show in Figure 3.3. Use netstat –rn or route –e to observe the changes that are being made to the routing tables. Save the output. Now disconnect the two cables that connect router 4 to the two Ethernets. See approx. how much time it takes RIP to alter the routing table in PC 52.100 to reflect the new topology. (Hint: use ping –s from PC 154.81.52.100 to PC 154.81.54.100 and see how long it takes till the alive message comes thru again after the disconnection. Check the routing table for new entries!)

 

Questions #6: 

 

·        Give the measured time from Exercise 6.

·        Compare the entries of the routing tables in the PCs and the routers with router4 connected and disconnected.

 

1.4         Mixed Router – Bridge Experiment

 

For this experiment you will configure two of the routers as bridges and two as routers as shown in Figure 3.4 below.

 

 

 

 

 

 

 

 

 

 


Figure 3.4 Router – Bridge Experiment

 

Four PCs are connected to 4 LANs (one PC per LAN). Two bridges  and two routers are interconnecting the 4 LANs. This a type “B” campus network and the network ID is: 132.143. 

 

 

Exercise 7

 

Flush all the routing tables and run RIP. Only three bits may be used for subnetting. Choose appropriate subnet IDs for the given configuration. Assign IP addresses to the bridge and router interfaces and the 4 PCs.

 

Questions #7:

 

 

Exercise 8

 

After RIP has run for awhile and you are able to reach all 4 PCs (use ping or traceroute), use netstat  -rn or route -e to show the routing tables in the PCs. Save the outputs. While running tethereal –V on PC1, PC2, PC3 and PC4, telnet from PC1 to PC3. Observe the packet flow between the two PCs.

 

Questions #8:

 

 

 

 

19:16:22.145945 154.81.51.3.route > 255.255.255.255.route: rip-resp 2:

154.81.53.0(1) 154.81.52.0(1)

                         4500 0048 0000 0000 0211 f947 825b 3d03

                         ffff ffff 0208 0208 0034 b859 0201 0000

                         0002 0000 825b 3f00 0000 0000 0000 0000

                         0000 0001 0002 0000 825b 3e00 0000 0000

                         0000 0000 0000 0001

19:16:23.145945 154.81.51.1.route > 255.255.255.255.route: rip-resp 1:

154.81.52.0(1)

                         4500 0034 0000 0000 0211 f95d 825b 3d01

                         ffff ffff 0208 0208 0020 0000 0201 0000

                         0002 0000 825b 3e00 0000 0000 0000 0000

                         0000 0001

 

 

ICMP-redirect

 

19:21:29.945945 154.81.51.1 > 154.81.51.100: icmp: redirect 154.81.53.3

to host 154.81.51.3

                         4500 0038 008e 0000 ff01 3c1b 825b 3d01

                         825b 3d64 0501 5580 825b 3d03 4500 0054

                         0fcd 0000 3f01 eabe 825b 3d64 825b 3f03

                         0800 071c d703 0000