In this tutorial, we will discuss the different reasons that cause the destination host unreachable in the Cisco packet tracer
Many times we encountered with destination host unreachable error when creating network topologies in packet tracer.
This error can also occur in case of hardware failures or faults however that is not so common.
As packet tracer is a simulation so we cannot have hardware failures in it so most of the time, this error is observed in packet tracer due to the following reasons.
Reason 1
Pinging IP address that does not exist on the network
Many times while testing our network, we mistype the commands and IP addresses so In case if we have mistyped the IP address that does not exist in our network will cause the Destination host unreachable error.
Fix – Make sure you have typed the destination IP correctly while pinging.
Reason 2
The router does not have an entry in the routing table
If the destination IP is on the other network then the router should have the information about that network in its routing table otherwise it will cause the destination host unreachable because even though the host exists but our device does not know how to reach the host.
If we will ping the Fast Ethernet 0/0 interface of router 4 from PC0 then we will get the unreachable error.
Download this Lab and try pinging the router 4 interface.
Fix – fix the issue by enabling routing dynamically or manually. Once router 3 will have information about the 192.168.3.0 network then router 3 will send the ping response.
Reason 3
Access list blocking the traffic
If traffic from any host is blocked by the access list then a destination host unreachable error will be received.
In the below example, traffic from host PC0 is blocked from reaching network 192.168.3.0 so the router is dropping the traffic received from this host, and ping packets are not able to reach the host PC1.
Download the lab and test the ping command and you will be able to see the packets blocked by the access list.
Fix – To fix the issue, either disable the access list or allow the traffic from PC0 on network 192.168.3.0
If we do not want to allow all traffic then only ICMP traffic can be blocked on the network. An extended access list can be used to block only ICMP traffic and allow the rest of the traffic from the host.
