Destination host unreachable in 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.
System Management Configuration Guide, Cisco IOS XE Amsterdam 17.3.x (Catalyst 9600 Switches)
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Book Title
System Management Configuration Guide, Cisco IOS XE Amsterdam 17.3.x (Catalyst 9600 Switches)
Troubleshooting the Software Configuration
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Chapter: Troubleshooting the Software Configuration
Troubleshooting the Software Configuration
This chapter describes how to identify and resolve software problems related to the Cisco IOS software on the switch. Depending on the nature of the problem, you can use the command-line interface (CLI), Device Manager, or Network Assistant to identify and solve problems.
Additional troubleshooting information, such as LED descriptions, is provided in the hardware installation guide.
Information About Troubleshooting the Software Configuration
Software Failure on a Switch
Switch software can be corrupted during an upgrade by downloading the incorrect file to the switch, and by deleting the image file. In all of these cases, there is no connectivity.
Lost or Forgotten Password on a Device
The default configuration for the device allows an end user with physical access to the device to recover from a lost password by interrupting the boot process during power-on and by entering a new password. These recovery procedures require that you have physical access to the device.
On these devices, a system administrator can disable some of the functionality of this feature by allowing an end user to reset a password only by agreeing to return to the default configuration. If you are an end user trying to reset a password when password recovery has been disabled, a status message reminds you to return to the default configuration during the recovery process.
You cannot recover encryption password key, when Cisco WLC configuration is copied from one Cisco WLC to another (in case of an RMA).
Follow the steps described in the section Recovering from a Lost or Forgotten Password to recover from a lost or forgotten password.
The device supports IP ping, which you can use to test connectivity to remote hosts. Ping sends an echo request packet to an address and waits for a reply. Ping returns one of these responses:
Normal response—The normal response ( hostname is alive) occurs in 1 to 10 seconds, depending on network traffic.
Destination does not respond—If the host does not respond, a no-answer message is returned.
Unknown host—If the host does not exist, an unknown host message is returned.
Destination unreachable—If the default gateway cannot reach the specified network, a destination-unreachable message is returned.
Network or host unreachable—If there is no entry in the route table for the host or network, a network or host unreachable message is returned.
Refere the section Executing Ping to understand how ping works.
Layer 2 Traceroute
The Layer 2 traceroute feature allows the switch to identify the physical path that a packet takes from a source device to a destination device. Layer 2 traceroute supports only unicast source and destination MAC addresses. Traceroute finds the path by using the MAC address tables of the devices in the path. When the Device detects a device in the path that does not support Layer 2 traceroute, the Device continues to send Layer 2 trace queries and lets them time out.
The Device can only identify the path from the source device to the destination device. It cannot identify the path that a packet takes from source host to the source device or from the destination device to the destination host.
Layer 2 Traceroute Guidelines
Cisco Discovery Protocol (CDP) must be enabled on all the devices in the network. For Layer 2 traceroute to function properly, do not disable CDP.
If any devices in the physical path are transparent to CDP, the switch cannot identify the path through these devices.
A device is reachable from another device when you can test connectivity by using the ping privileged EXEC command. All devices in the physical path must be reachable from each other.
The maximum number of hops identified in the path is ten.
You can enter the traceroute mac or the traceroute mac ip privileged EXEC command on a device that is not in the physical path from the source device to the destination device. All devices in the path must be reachable from this switch.
The traceroute mac command output shows the Layer 2 path only when the specified source and destination MAC addresses belong to the same VLAN. If you specify source and destination MAC addresses that belong to different VLANs, the Layer 2 path is not identified, and an error message appears.
If you specify a multicast source or destination MAC address, the path is not identified, and an error message appears.
If the source or destination MAC address belongs to multiple VLANs, you must specify the VLAN to which both the source and destination MAC addresses belong. If the VLAN is not specified, the path is not identified, and an error message appears.
The traceroute mac ip command output shows the Layer 2 path when the specified source and destination IP addresses belong to the same subnet. When you specify the IP addresses, the device uses the Address Resolution Protocol (ARP) to associate the IP addresses with the corresponding MAC addresses and the VLAN IDs.
If an ARP entry exists for the specified IP address, the device uses the associated MAC address and identifies the physical path.
If an ARP entry does not exist, the device sends an ARP query and tries to resolve the IP address. If the IP address is not resolved, the path is not identified, and an error message appears.
When multiple devices are attached to one port through hubs (for example, multiple CDP neighbors are detected on a port), the Layer 2 traceroute feature is not supported. When more than one CDP neighbor is detected on a port, the Layer 2 path is not identified, and an error message appears.
This feature is not supported in Token Ring VLANs.
Layer 2 traceroute opens a listening socket on the User Datagram Protocol (UDP) port 2228 that can be accessed remotely with any IPv4 address, and does not require any authentication. This UDP socket allows to read VLAN information, links, presence of particular MAC addresses, and CDP neighbor information, from the device. This information can be used to eventually build a complete picture of the Layer 2 network topology.
Layer 2 traceroute is enabled by default and can be disabled by running the no l2 traceroute command in global configuration mode. To re-enable Layer 2 traceroute, use the l2 traceroute command in global configuration mode.
IP Traceroute
You can use IP traceroute to identify the path that packets take through the network on a hop-by-hop basis. The command output displays all network layer (Layer 3) devices, such as routers, that the traffic passes through on the way to the destination.
Your Device can participate as the source or destination of the traceroute privileged EXEC command and might or might not appear as a hop in the traceroute command output. If the Device is the destination of the traceroute, it is displayed as the final destination in the traceroute output. Intermediate devices do not show up in the traceroute output if they are only bridging the packet from one port to another within the same VLAN. However, if the intermediate Device is a multilayer Device that is routing a particular packet, this device shows up as a hop in the traceroute output.
The traceroute privileged EXEC command uses the Time To Live (TTL) field in the IP header to cause routers and servers to generate specific return messages. Traceroute starts by sending a User Datagram Protocol (UDP) datagram to the destination host with the TTL field set to 1. If a router finds a TTL value of 1 or 0, it drops the datagram and sends an Internet Control Message Protocol (ICMP) time-to-live-exceeded message to the sender. Traceroute finds the address of the first hop by examining the source address field of the ICMP time-to-live-exceeded message.
To identify the next hop, traceroute sends a UDP packet with a TTL value of 2. The first router decrements the TTL field by 1 and sends the datagram to the next router. The second router sees a TTL value of 1, discards the datagram, and returns the time-to-live-exceeded message to the source. This process continues until the TTL is incremented to a value large enough for the datagram to reach the destination host (or until the maximum TTL is reached).
To learn when a datagram reaches its destination, traceroute sets the UDP destination port number in the datagram to a very large value that the destination host is unlikely to be using. When a host receives a datagram destined to itself containing a destination port number that is unused locally, it sends an ICMP port-unreachable error to the source. Because all errors except port-unreachable errors come from intermediate hops, the receipt of a port-unreachable error means that this message was sent by the destination port.
Go to Example: Performing a Traceroute to an IP Host to see an example of IP traceroute process.
Debug Commands
Because debugging output is assigned high priority in the CPU process, it can render the system unusable. For this reason, use debug commands only to troubleshoot specific problems or during troubleshooting sessions with Cisco technical support staff. It is best to use debug commands during periods of lower network traffic and fewer users. Debugging during these periods decreases the likelihood that increased debug command processing overhead will affect system use.
All debug commands are entered in privileged EXEC mode, and most debug commands take no arguments.
System Report
System reports or crashinfo files save information that helps Cisco technical support representatives to debug problems that caused the Cisco IOS image to fail (crash). It is necessary to quickly and reliably collect critical crash information with high fidelity and integrity. Further, it is necessary to collect this information and bundle it in a way that it can be associated or identified with a specific crash occurrence.
System reports are generated in case of a switchover: System reports are generated only on high availability (HA) member switches. Reports are not generated for non-HA members.
The system does not generate reports in case of a reload.
During a process crash, the following is collected locally from the switch:
Full process core
IOS syslogs (not guaranteed in case of non-active crashes)
System process information
Certain types of /proc information
This information is stored in separate files which are then archived and compressed into one bundle. This makes it convenient to get a crash snapshot in one place, and can be then moved off the box for analysis. This report is generated before the switch goes down to rommon/bootloader.
Except for the full core and tracelogs, everything else is a text file.
Use the request platform software process core fed switch active command to generate the core dump.
Crashinfo Files
By default the system report file will be generated and saved into the /crashinfo directory. Ifit cannot be saved to the crashinfo partition for lack of space, then it will be saved to the /flash directory.
To display the files, enter the dir crashinfo: command. The following is sample output of a crashinfo directory:
System reports are located in the crashinfo directory in the following format:
After a switch crashes, check for a system report file. The name of the most recently generated system report file is stored in the last_systemreport file under the crashinfo directory. The system report and crashinfo files assist TAC while troubleshooting the issue.
The system report generated can be further copied using TFTP, HTTP and few other options.
The general syntax for copying onto TFTP server is as follows:
The tracelogs can be collected by issuing a trace archive command. This command provides time period options. The command syntax is as follows:
The tracelogs stored in crashinfo: or flash: directory from within the last 3650 days can be collected.
It is important to clear the system reports or trace archives from flash or crashinfo directory once they are copied out, in order to have space available for tracelogs and other purposes.
In a complex network it is difficult to track the origin of a system-report file. This task is made easier if the system-report files are uniquely identifiable. Starting with the Cisco IOS XE Amsterdam 17.3.x release, the hostname will be prepended to the system-report file name making the reports uniquely identifiable.
The following example displays system-report files with the hostname prepended:
Onboard Failure Logging on the Switch
You can use the onboard failure logging (OBFL) feature to collect information about the device. The information includes uptime, temperature, and voltage information and helps Cisco technical support representatives to troubleshoot device problems. We recommend that you keep OBFL enabled and do not erase the data stored in the flash memory.
By default, OBFL is enabled. It collects information about the device and small form-factor pluggable (SFP) modules. The device stores this information in the flash memory:
CLI commands—Record of the OBFL CLI commands that are entered on a standalone device.
Message—Record of the hardware-related system messages generated by a standalone device .
Power over Ethernet (PoE)—Record of the power consumption of PoE ports on a standalone device .
Temperature—Temperature of a standalone deicev .
Uptime data—Time when a standalone device starts, the reason the device restarts, and the length of time the device has been running since it last restarted.
Voltage—System voltages of a standalone device .
You should manually set the system clock or configure it by using Network Time Protocol (NTP).
When the device is running, you can retrieve the OBFL data by using the show logging onboard privileged EXEC commands. If the device fails, contact your Cisco technical support representative to find out how to retrieve the data.
When an OBFL-enabled device is restarted, there is a 10-minute delay before logging of new data begins.
Fan Failures
By default, the feature is disabled. When more than one of the fans fails in a field-replaceable unit (FRU) or in a power supply, the device does not shut down, and this error message appears:
The device might overheat and shut down.
To restart the device, it must be power cycled.
Possible Symptoms of High CPU Utilization
Excessive CPU utilization might result in these symptoms, but the symptoms might also result from other causes, some of which are the following:
Spanning tree topology changes
EtherChannel links brought down due to loss of communication
Failure to respond to management requests (ICMP ping, SNMP timeouts, slow Telnet or SSH sessions)
IP SLAs failures because of SLAs responses beyond an acceptable threshold
DHCP or IEEE 802.1x failures if the switch does not forward or respond to requests
How to Troubleshoot the Software Configuration
Recovering from a Lost or Forgotten Password
The default configuration for the switch allows an end user with physical access to the switch to recover from a lost password by interrupting the boot process during power-on and by entering a new password. These recovery procedures require that you have physical access to the switch.
On these switches, a system administrator can disable some of the functionality of this feature by allowing an end user to reset a password only by agreeing to return to the default configuration. If you are an end user trying to reset a password when password recovery has been disabled, a status message shows this during the recovery process.
Procedure
Connect a terminal or PC to the switch.
Connect a terminal or a PC with terminal-emulation software to the switch console port.
Connect a PC to the Ethernet management port.
Set the line speed on the emulation software to 9600 baud.
Power off the standalone switch or the entire switch stack.
Reconnect the power cord to the switch or the active switch. For a device with dual supervisor module, remove the standy supervisor from the chassis before the password recovery procedure. Reconnect the power cord to the switch or the active supervisor module. Press Ctrl-C to prevent autoboot and to get into ROMMON mode while the switch or the active supervisor module is booting up.
Proceed to the Procedure with Password Recovery Enabled section, and follow the steps.
After recovering the password, reload the switch or the active switch.
Procedure with Password Recovery Enabled
Procedure
Ignore the startup configuration with the following command:
Boot the switch with the packages.conf file from flash.
Terminate the initial configuration dialog by answering No.
At the switch prompt, enter privileged EXEC mode.
Copy the startup configuration to running configuration.
Press Return in response to the confirmation prompts. The configuration file is now reloaded, and you can change the password.
Enter global configuration mode and change the enable password.
Return to privileged EXEC mode:
Write the running configuration to the startup configuration file.
Confirm that manual boot mode is enabled.
Reload the device.
Set the SWITCH_IGNORE_STARTUP_CFG parameter to 0.
Boot the device with the packages.conf file from flash.
After the device boots up, disable manual boot on the device.
Procedure with Password Recovery Disabled
If the password-recovery mechanism is disabled, this message appears:
Returning the device to the default configuration results in the loss of all existing configurations. We recommend that you contact your system administrator to verify if there are backup device and VLAN configuration files.
If you enter n (no), the normal boot process continues as if the Mode button had not been pressed; you cannot access the boot loader prompt, and you cannot enter a new password. You see the message:
If you enter y (yes), the configuration file in flash memory and the VLAN database file are deleted. When the default configuration loads, you can reset the password.
Procedure
Choose to continue with password recovery and delete the existing configuration:
Display the contents of flash memory:
The device file system appears.
Boot up the system:
You are prompted to start the setup program. To continue with password recovery, enter N at the prompt:
At the device prompt, enter privileged EXEC mode:
Enter global configuration mode:
Change the password:
The secret password can be from 1 to 25 alphanumeric characters, can start with a number, is case sensitive, and allows spaces but ignores leading spaces.
Return to privileged EXEC mode:
Write the running configuration to the startup configuration file:
The new password is now in the startup configuration.
You must now reconfigure the device. If the system administrator has the backup device and VLAN configuration files available, you should use those.
Preventing Autonegotiation Mismatches
The IEEE 802.3ab autonegotiation protocol manages the device settings for speed (10 Mb/s, 100 Mb/s, and 1000 Mb/s, excluding SFP module ports) and duplex (half or full). There are situations when this protocol can incorrectly align these settings, reducing performance. A mismatch occurs under these circumstances:
A manually set speed or duplex parameter is different from the manually set speed or duplex parameter on the connected port.
A port is set to autonegotiate, and the connected port is set to full duplex with no autonegotiation.
To maximize the device performance and ensure a link, follow one of these guidelines when changing the settings for duplex and speed:
Let both ports autonegotiate both speed and duplex.
Manually set the speed and duplex parameters for the ports on both ends of the connection.
If a remote device does not autonegotiate, configure the duplex settings on the two ports to match. The speed parameter can adjust itself even if the connected port does not autonegotiate.
Troubleshooting SFP Module Security and Identification
Cisco small form-factor pluggable (SFP) modules have a serial EEPROM that contains the module serial number, the vendor name and ID, a unique security code, and cyclic redundancy check (CRC). When an SFP module is inserted in the device, the device software reads the EEPROM to verify the serial number, vendor name and vendor ID, and recompute the security code and CRC. If the serial number, the vendor name or vendor ID, the security code, or CRC is invalid, the software generates a security error message and places the interface in an error-disabled state.
The security error message references the GBIC_SECURITY facility. The device supports SFP modules and does not support GBIC modules. Although the error message text refers to GBIC interfaces and modules, the security messages actually refer to the SFP modules and module interfaces.
If you are using a non-Cisco SFP module, remove the SFP module from the device, and replace it with a Cisco module. After inserting a Cisco SFP module, use the errdisable recovery cause gbic-invalid global configuration command to verify the port status, and enter a time interval for recovering from the error-disabled state. After the elapsed interval, the device brings the interface out of the error-disabled state and retries the operation. For more information about the errdisable recovery command, see the command reference for this release.
If the module is identified as a Cisco SFP module, but the system is unable to read vendor-data information to verify its accuracy, an SFP module error message is generated. In this case, you should remove and reinsert the SFP module. If it continues to fail, the SFP module might be defective.
Executing Ping
If you attempt to ping a host in a different IP subnetwork, you must define a static route to the network or have IP routing configured to route between those subnets.
IP routing is disabled by default on all devices.
Though other protocol keywords are available with the ping command, they are not supported in this release.
Use this command to ping another device on the network from the device:
ping ip host | address
Pings a remote host through IP or by supplying the hostname or network address.
Monitoring Temperature
The Device monitors the temperature conditions and uses the temperature information to control the fans.
Monitoring the Physical Path
You can monitor the physical path that a packet takes from a source device to a destination device by using one of these privileged EXEC commands:
tracetroute mac [ interface interface-id ] < source-mac-address >[ interface interface-id ] < destination-mac-address >[ vlan vlan-id ] [ detail ]
Displays the Layer 2 path taken by the packets from the specified source MAC address to the specified destination MAC address.
Displays the Layer 2 path taken by the packets from the specified source IP address or hostname to the specified destination IP address or hostname.
Executing IP Traceroute
Though other protocol keywords are available with the traceroute privileged EXEC command, they are not supported in this release.
traceroute ip host
Traces the path that packets take through the network.
Redirecting Debug and Error Message Output
By default, the network server sends the output from debug commands and system error messages to the console. If you use this default, you can use a virtual terminal connection to monitor debug output instead of connecting to the console port .
Possible destinations include the console, virtual terminals, internal buffer, and UNIX hosts running a syslog server. The syslog format is compatible with 4.3 Berkeley Standard Distribution (BSD) UNIX and its derivatives.
Be aware that the debugging destination you use affects system overhead. When you log messages to the console, very high overhead occurs. When you log messages to a virtual terminal, less overhead occurs. Logging messages to a syslog server produces even less, and logging to an internal buffer produces the least overhead of any method.
For more information about system message logging, see Configuring System Message Logging .
Using the show platform Command
The output from the show platform privileged EXEC command provides some useful information about the forwarding results if a packet entering an interface is sent through the system. Depending upon the parameters entered about the packet, the output provides lookup table results and port maps used to calculate forwarding destinations, bitmaps, and egress information.
Most of the information in the output from the command is useful mainly for technical support personnel, who have access to detailed information about the device application-specific integrated circuits (ASICs). However, packet forwarding information can also be helpful in troubleshooting.
Using the show debug command
The show debug command is entered in privileged EXEC mode. This command displays all debug options available on the switch.
To view all conditional debug options run the command show debug condition The commands can be listed by selecting either a condition identifier <1-1000> or all conditions.
To disable debugging, use the no debug all command.
Because debugging output is assigned high priority in the CPU process, it can render the system unusable. For this reason, use debug commands only to troubleshoot specific problems or during troubleshooting sessions with Cisco technical support staff. Moreover, it is best to use debug commands during periods of lower network traffic and fewer users. Debugging during these periods decreases the likelihood that increased debug command processing overhead will affect system use.
Verifying Troubleshooting of the Software Configuration
Displaying OBFL Information
show logging onboard RP active clilog [ continuous | detail | summary ]
Displays the OBFL CLI commands that were entered on a module.
show logging onboard RP active environment [ continuous | detail | summary ]
Displays the UDI information for a module and for all the connected FRU devices: the PID, the VID, and the serial number.
show logging onboard RP active message [ continuous | detail | summary ]
Displays the hardware-related messages generated by a module.
show logging onboard RP active counter [ continuous | detail | summary ]
Displays the counter information on a module.
show logging onboard RP active temperature [ continuous | detail | summary ]
Displays the temperature information of a module.
show logging onboard RP active uptime [ continuous | detail | summary ]
Displays the time when a module start, the reason the module restart, and the length of time that the module have been running since they last restarted.
show logging onboard RP active voltage [ continuous | detail | summary ]
Displays the system voltages of a module.
show logging onboard RP active status [ continuous | detail | summary ]
Displays the status of each OBFL application of a module.
Example: Verifying the Problem and Cause for High CPU Utilization
To determine if high CPU utilization is a problem, enter the show processes cpu sorted privileged EXEC command. Note the underlined information in the first line of the output example.
This example shows normal CPU utilization. The output shows that utilization for the last 5 seconds is 8%/0%, which has this meaning:
The total CPU utilization is 8 percent, including both time running Cisco IOS processes and time spent handling interrupts.
The time spent handling interrupts is zero percent.
Type of Problem
Interrupt percentage value is almost as high as total CPU utilization value.
The CPU is receiving too many packets from the network.
Determine the source of the network packet. Stop the flow, or change the switch configuration. See the section on “Analyzing Network Traffic.”
Total CPU utilization is greater than 50% with minimal time spent on interrupts.
One or more Cisco IOS process is consuming too much CPU time. This is usually triggered by an event that activated the process.
Identify the unusual event, and troubleshoot the root cause. See the section on “Debugging Active Processes.”
Configuration Examples for Troubleshooting Software
Example: Pinging an IP Host
This example shows how to ping an IP host:
Each exclamation point means receipt of a reply.
Each period means the network server timed out while waiting for a reply.
A destination unreachable error PDU was received.
A congestion experienced packet was received.
User interrupted test.
Unknown packet type.
Packet lifetime exceeded.
To end a ping session, enter the escape sequence (Ctrl-^ X by default). Simultaneously press and release the Ctrl, Shift, and 6 keys and then press the X key.
Example: Performing a Traceroute to an IP Host
This example shows how to perform a traceroute to an IP host:
The display shows the hop count, the IP address of the router, and the round-trip time in milliseconds for each of the three probes that are sent.
The probe timed out.
Unknown packet type.
Administratively unreachable. Usually, this output means that an access list is blocking traffic.
How to Fix Destination Host Unreachable Error?
Do you know the most difficult part of the job of a network engineer? You are responsible for every issue related to networking in your company. Even though everything works fine, someone will come up with a complaint, and it is on our head to fix it.
While I was working as a network engineer trainee, I received a call from the development section. The manager on Duty in the development section was angry and said that the network was not working.
When I asked him about the issue, he said the Internet is just fine, but one of his teammates received an error while pinging to a device in his subnet.
His teammate received the Destination Host Unreachable reply while he tried to ping to another computer in his section.
The manager on Duty demanded an explanation for the Destination Host Unreachable. I explained to him the reasons to receive Destination Host Unreachable error messages with examples. If you have not seen this error message before, have a look at the screenshot attached below.
What Is The Reason to Receive Destination Host Unreachable Error Message?
If you want a one-sentence answer, look at the statement in the table.
Either there is no device with the IP Address you typed or your computer has a corrupted ARP table.
Let me explain with the example I showed above. When I sent Ping packets to the IP address 192.168.225.45 from my computer, it looked at the ARP table stored in my PC to fetch the MAC address associated with the destination IP Address.
You know the basic rule of network communication. You cannot send packets to an IP Address before finding the MAC address (Physical Address) of the destination device.
ARP table shows the MAC address of the devices assigned with the specific IP Address.
If you do not know this concept, there are tons of tutorials available about Address Resolution Protocol (ARP) on the Internet.
My computer could not find the ARP Address mapped to the IP Address 192.168.225.45 in the ARP table.
So it displayed Reply from 192.168.225.47: Destination host unreachable as the response.
How to Fix Destination Host Unreachable?
If you do not know how to fix the reply from the x.x.x.x destination host unreachable message, follow the instructions provided below.
The first step to troubleshoot the Reply from 192.168.225.47: Destination host unreachable error is by deleting all entries in the ARP table on your computer.
-
Open the Command Prompt as Administrator
-
Type cmd on the Windows Search
If the problem persists, you should run a traceroute to pinpoint the problem location.
-
Open Command Prompt
In my experience, some users said faulty Firewall settings caused the Destination Host Unreachable error. So, I suggest you turn off the firewall on your laptop and check for the issue.
If the destination device is in your reach, make sure the device is on. Make sure the network connection is fine.
How to Check if Destination a Host Unreachable Error is Resolved?
It is very simple. You need to ping the same IP Address.
If the error is at the side of the IP Address, you should try to ping a different IP Address or domain name.
For example, check the command below to test whether the Destination a Host Unreachable Error fixed or not.
About The Author:
Siju George is a Cisco and Microsoft certified Network Engineer. He has been working in the Network Engineering field since 2006.
Understanding Ping Responses,Destination unreachable,Request timed out,Reply
Here we are going to see ping responses network unreachable,request timed out,success with a simple topology by adding static route on each router step by step.
Step 1:Create a topology like this
Step 2:Routers only knows directly connected network,there is no static route added.Now, ping default gate way 10.0.0.1 from Host 10.0.0.10. we will get reply from 10.0.0.1.Because router knows 10.0.0.0 network.
PC>ping 10.0.0.1
Pinging 10.0.0.1 with 32 bytes of data:
Reply from 10.0.0.1: bytes=32 time=157ms TTL=255
Reply from 10.0.0.1: bytes=32 time=16ms TTL=255
Reply from 10.0.0.1: bytes=32 time=29ms TTL=255
Reply from 10.0.0.1: bytes=32 time=31ms TTL=255
Ping statistics for 10.0.0.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 16ms, Maximum = 157ms, Average = 58ms
Step 3:Now ping host 40.0.0.10,we will get
PC>ping 40.0.0.10
Pinging 40.0.0.10 with 32 bytes of data:
Reply from 10.0.0.1: Destination host unreachable.
Reply from 10.0.0.1: Destination host unreachable.
Reply from 10.0.0.1: Destination host unreachable.
Reply from 10.0.0.1: Destination host unreachable.
Ping statistics for 40.0.0.10:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
Step 4:Add static route to Router R1 for the network 40.0.0.0
R1(config)#ip route 40.0.0.0 255.0.0.0 20.0.0.2
Now,Packets that came to Router R1 for the network 40.0.0.0 will be forwarded to 20.0.0.2
Check Routing table of R1 by giving command,
R1#show ip route
Codes: C — connected, S — static, I — IGRP, R — RIP, M — mobile, B — BGP
D — EIGRP, EX — EIGRP external, O — OSPF, IA — OSPF inter area
N1 — OSPF NSSA external type 1, N2 — OSPF NSSA external type 2
E1 — OSPF external type 1, E2 — OSPF external type 2, E — EGP
i — IS-IS, L1 — IS-IS level-1, L2 — IS-IS level-2, ia — IS-IS inter area
* — candidate default, U — per-user static route, o — ODR
P — periodic downloaded static route
Gateway of last resort is not set
C 10.0.0.0/8 is directly connected, FastEthernet0/0
C 20.0.0.0/8 is directly connected, Serial2/0
S 40.0.0.0/8 [1/0] via 20.0.0.2
We get reply from 20.0.0.1 because router R1 knows directly connected network.
Step 6:Now ping ip address 20.0.0.2
PC>ping 20.0.0.2
Pinging 20.0.0.2 with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Ping statistics for 20.0.0.2:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
Router R2 doesn’t know about the network 10.0.0.0.So we can’t get reply from R2.Now add static route to router R2 for network 10.0.0.0 .Check routing table of R2
R2#show ip route
Codes: C — connected, S — static, I — IGRP, R — RIP, M — mobile, B — BGP
D — EIGRP, EX — EIGRP external, O — OSPF, IA — OSPF inter area
N1 — OSPF NSSA external type 1, N2 — OSPF NSSA external type 2
E1 — OSPF external type 1, E2 — OSPF external type 2, E — EGP
i — IS-IS, L1 — IS-IS level-1, L2 — IS-IS level-2, ia — IS-IS inter area
* — candidate default, U — per-user static route, o — ODR
P — periodic downloaded static route
Gateway of last resort is not set
C 20.0.0.0/8 is directly connected, Serial2/0
C 30.0.0.0/8 is directly connected, Serial3/