This article is all about how to configure null routing on Cisco routers in Cisco packet tracer. In other words, null o routing is also known as black hole routing configuration over the Cisco routers. In computer networking, a null route or black hole route is a network route that goes nowhere. Matching packets are dropped (ignored) rather than forwarded, acting as a kind of very limited firewall. Null routing is acting as a black hole on the routers because it sends unwanted packets from a certain network to black hole without reaching them to the receiver. It diverts all the packets to the black hole from where it never come back again. It is a type of trash or Recycles Bin for route packets. Basically, companies used this to drop some specific network to stop the DDOS attack. All the traffic from an unwanted network is sent to the null interface is discarded. Network admin used it to discard traffic simply by routing it to the null interface.
Also Read: How to automatic secure your router using the auto secure feature
Now here we take a lab in cisco packet tracer to understand null routing or black hole routing easily.
In this lab, we take three routers and three PCs. Here Pcs are used to check null routing on your system. First of all, we assign IP address on all the interfaces of the routers and after that, we configure null routing to a certain router to stop DDOS attacks and divert heavy unwanted traffic into a black hole. After that, we assign an IP address to the PCs using static method and check whether null routing is work properly or not on the routers. Like here in this tutorial I am going to block packets generated from router R2 4.0.0.o network for 8.0.0.0 network.
Now, first of all, we assign the IP address to all the interfaces of the routers and up all the routers using no shut command.
For router R1
— System Configuration Dialog —
Continue with configuration dialog? [yes/no]: NO
Press RETURN to get started!
Router>enable
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#hostname R1
R1(config)#interface FastEthernet0/0
R1(config-if)#ip address 1.0.0.1 255.0.0.0
R1(config-if)#no shutdown
%LINK-5-CHANGED: Interface FastEthernet0/0, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
R1(config-if)#exit
R1(config)#interface Serial0/0/0
R1(config-if)#no ip address
R1(config-if)#ip address 2.0.0.1 255.0.0.0
R1(config-if)#no shutdown
%LINK-5-CHANGED: Interface Serial0/0/0, changed state to down
R1(config-if)#exit
R1(config)#interface Serial0/0/1
R1(config-if)#ip address 3.0.0.1 255.0.0.0
R1(config-if)#no shutdown
%LINK-5-CHANGED: Interface Serial0/0/1, changed state to down
R1(config-if)#exit
For router R2
— System Configuration Dialog —
Continue with configuration dialog? [yes/no]: no
Press RETURN to get started!
Router>enable
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#hostname R2
R2(config)#interface FastEthernet0/0
R2(config-if)#ip address 4.0.0.1 255.0.0.0
R2(config-if)#no shutdown
R2(config-if)#
%LINK-5-CHANGED: Interface FastEthernet0/0, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
R2(config-if)#exit
R2(config)#interface Serial0/0/0
R2(config-if)#ip address 2.0.0.2 255.0.0.0
R2(config-if)#no shutdown
R2(config-if)#
%LINK-5-CHANGED: Interface Serial0/0/0, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/0, changed state to up
R2(config-if)#exit
R2(config)#interface Serial0/0/1
R2(config)#ip address 5.0.0.1 255.0.0.0
R2(config-if)#no shutdown
%LINK-5-CHANGED: Interface Serial0/0/1, changed state to down
R2(config-if)#exit
For router R3
— System Configuration Dialog —
Continue with configuration dialog? [yes/no]: no
Press RETURN to get started!
Router>enable
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#hostname R3
R3(config)#interface FastEthernet0/0
R3(config-if)#ip address 6.0.0.1 255.0.0.0
R3(config-if)#no shutdown
%LINK-5-CHANGED: Interface FastEthernet0/0, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
R3(config-if)#exit
R3(config)#interface Serial0/0/0
R3(config-if)#ip address 7.0.0.1 255.0.0.0
R3(config-if)#no shutdown
%LINK-5-CHANGED: Interface Serial0/0/0, changed state to down
R3(config-if)#exit
R3(config)#interface Serial0/0/1
R3(config-if)#ip address 5.0.0.2 255.0.0.0
R3(config-if)#no shutdown
%LINK-5-CHANGED: Interface Serial0/0/1, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/1, changed state to up
R3(config-if)#exit
For router R4
— System Configuration Dialog —
Continue with configuration dialog? [yes/no]: no
Press RETURN to get started!
Router>enable
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#hostname R4
R4(config)#interface FastEthernet0/0
R4(config-if)#ip address 8.0.0.1 255.0.0.0
R4(config-if)#no shutdown
%LINK-5-CHANGED: Interface FastEthernet0/0, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up
R4(config-if)#exit
R4(config)#interface Serial0/0/0
R4(config-if)#ip address 7.0.0.2 255.0.0.0
R4(config-if)#no shutdown
%LINK-5-CHANGED: Interface Serial0/0/0, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/0, changed state to up
R4(config-if)#exit
R4(config)#interface Serial0/0/1
R4(config-if)#ip address 3.0.0.2 255.0.0.0
R4(config-if)#no shutdown
%LINK-5-CHANGED: Interface Serial0/0/1, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/1, changed state to up
R4(config-if)#exit
Now we configure routing on the routers in the given below manner on the routers
For router R1
R1(config)#ip route 4.0.0.0 255.0.0.0 2.0.0.2
R1(config)#ip route 5.0.0.0 255.0.0.0 2.0.0.2
R1(config)#ip route 6.0.0.0 255.0.0.0 5.0.0.2
R1(config)#ip route 8.0.0.0 255.0.0.0 3.0.0.2
R1(config)#ip route 7.0.0.0 255.0.0.0 3.0.0.2
For router R2
R2(config)#ip route 1.0.0.0 255.0.0.0 2.0.0.1
R2(config)#ip route 3.0.0.0 255.0.0.0 2.0.0.1
R2(config)#ip route 6.0.0.0 255.0.0.0 5.0.0.2
R2(config)#ip route 8.0.0.0 255.0.0.0 3.0.0.2
R2(config)#ip route 7.0.0.0 255.0.0.0 null0
For router R3
R3(config)#ip route 4.0.0.0 255.0.0.0 5.0.0.1
R3(config)#ip route 2.0.0.0 255.0.0.0 5.0.0.1
R3(config)#ip route 8.0.0.0 255.0.0.0 7.0.0.2
R3(config)#ip route 3.0.0.0 255.0.0.0 7.0.0.2
R3(config)#ip route 1.0.0.0 255.0.0.0 3.0.0.1
For router R4
R4(config)#ip route 6.0.0.0 255.0.0.0 7.0.0.1
R4(config)#ip route 5.0.0.0 255.0.0.0 7.0.0.1
R4(config)#ip route 1.0.0.0 255.0.0.0 3.0.0.1
R4(config)#ip route 2.0.0.0 255.0.0.0 3.0.0.1
R4(config)#ip route 4.0.0.0 255.0.0.0 2.0.0.2
Now all the routers will be configured correctly usn null router. Now assign IP address to all the PCs to complete this lab and the use ping command on the PC which is directly connected through the router R2
Now check whether null routing is configured on the routers or not using the ping command, As the given below
Packet Tracer PC Command Line 1.0
PC>ping 8.0.0.2
Pinging 8.0.0.2 with 32 bytes of data:
Reply from 4.0.0.1: Destination host unreachable.
Reply from 4.0.0.1: Destination host unreachable.
Reply from 4.0.0.1: Destination host unreachable.
Reply from 4.0.0.1: Destination host unreachable.
Ping statistics for 8.0.0.2:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
THAT’S IT
if this type of result will be shown on your screen that means your null routing configured successfully on the routers. If you have any queries regarding this simply solved out through the comment section and also provide feedback to us because your feedback is valuable for us.
