IntroductionThis document describes the use of the ping and traceroute commands on Cisco routers. Show
PrerequisitesRequirementsThere are no specific requirements for this document. Components UsedThis document is not restricted to specific software and hardware versions. The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command. ConventionsFor more information on document conventions, refer to the Cisco Technical Tips Conventions . Background InformationNote: Any debug command used on a production router can cause serious problems. Read the Use the Debug Command section before you issue debug commands. In this document, this basic configuration is used for examples in this article:
The Ping CommandThe ping command is a very common method used to troubleshoot accessibility of devices. It uses a series of Internet Control Message Protocol (ICMP) Echo messages to determine:
The ping command first sends an echo request packet to an address, then waits for a reply. The ping is successful only if:
The TTL value of a ping packet cannot be changed. This next code example shows the ping command after the debug ip packet detail command is enabled. Warning: When the debug ip packet detail command is used on a production router it can cause high CPU utilization. This can result in a severe performance degradation or a network outage. Router1#debug ip packet detail IP packet debugging is on (detailed) Router1#ping 172.16.0.12 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.0.12, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 4/6/8 ms Router1# Jan 20 15:54:47.487: IP: s=172.16.12.1 (local), d=172.16.0.12 (Serial0), len 100, sending Jan 20 15:54:47.491: ICMP type=8, code=0 !--- This is the ICMP packet 172.16.12.1 sent to 172.16.0.12. Possible ICMP-type Values
Possible Output Characters From the Ping Facility
Unable to PingIf you are not able to successfully ping to an IP address, consider the causes listed in this section. Router IssueHere are examples of unsuccessful ping attempts, that can determine the problem, and what to do to resolve the problem. This example is shown with this network topology diagram:
Try to ping Router4 from Router1: Router1#ping 172.16.4.34 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.4.34, timeout is 2 seconds: ..... Success rate is 0 percent (0/5) Results: Router1#debug ip packet IP packet debugging is on Warning: When the debug ip packet command is used on a production router it can cause high CPU utilization. This can result in a severe performance degradation or a network outage. Router1#ping 172.16.4.34 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.4.34, timeout is 2 seconds: Jan 20 16:00:25.603: IP: s=172.16.12.1 (local), d=172.16.4.34, len 100, unroutable. Jan 20 16:00:27.599: IP: s=172.16.12.1 (local), d=172.16.4.34, len 100, unroutable. Jan 20 16:00:29.599: IP: s=172.16.12.1 (local), d=172.16.4.34, len 100, unroutable. Jan 20 16:00:31.599: IP: s=172.16.12.1 (local), d=172.16.4.34, len 100, unroutable. Jan 20 16:00:33.599: IP: s=172.16.12.1 (local), d=172.16.4.34, len 100, unroutable. Success rate is 0 percent (0/5) Since no routing protocols run on Router1, it does not know where to send its packet and causes an "unrouteable" message. Add a static route to Router1: Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#ip route 0.0.0.0 0.0.0.0 Serial0 Results: Router1#debug ip packet detail IP packet debugging is on (detailed) Router1#ping 172.16.4.34 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.4.34, timeout is 2 seconds: U.U.U Success rate is 0 percent (0/5) Jan 20 16:05:30.659: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending Jan 20 16:05:30.663: ICMP type=8, code=0 Jan 20 16:05:30.691: IP: s=172.16.0.12 (Serial0), d=172.16.12.1 (Serial0), len 56, rcvd 3 Jan 20 16:05:30.695: ICMP type=3, code=1 Jan 20 16:05:30.699: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending Jan 20 16:05:30.703: ICMP type=8, code=0 Jan 20 16:05:32.699: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending Jan 20 16:05:32.703: ICMP type=8, code=0 Jan 20 16:05:32.731: IP: s=172.16.0.12 (Serial0), d=172.16.12.1 (Serial0), len 56, rcvd 3 Jan 20 16:05:32.735: ICMP type=3, code=1 Jan 20 16:05:32.739: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending Jan 20 16:05:32.743: ICMP type=8, code=0 Examine what is wrong on Router2: Router2#debug ip packet detail IP packet debugging is on (detailed) Router2# Jan 20 16:10:41.907: IP: s=172.16.12.1 (Serial1), d=172.16.4.34, len 100, unroutable Jan 20 16:10:41.911: ICMP type=8, code=0 Jan 20 16:10:41.915: IP: s=172.16.0.12 (local), d=172.16.12.1 (Serial1), len 56, sending Jan 20 16:10:41.919: ICMP type=3, code=1 Jan 20 16:10:41.947: IP: s=172.16.12.1 (Serial1), d=172.16.4.34, len 100, unroutable Jan 20 16:10:41.951: ICMP type=8, code=0 Jan 20 16:10:43.943: IP: s=172.16.12.1 (Serial1), d=172.16.4.34, len 100, unroutable Jan 20 16:10:43.947: ICMP type=8, code=0 Jan 20 16:10:43.951: IP: s=172.16.0.12 (local), d=172.16.12.1 (Serial1), len 56, sending Jan 20 16:10:43.955: ICMP type=3, code=1 Jan 20 16:10:43.983: IP: s=172.16.12.1 (Serial1), d=172.16.4.34, len 100, unroutable Jan 20 16:10:43.987: ICMP type=8, code=0 Jan 20 16:10:45.979: IP: s=172.16.12.1 (Serial1), d=172.16.4.34, len 100, unroutable Jan 20 16:10:45.983: ICMP type=8, code=0 Jan 20 16:10:45.987: IP: s=172.16.0.12 (local), d=172.16.12.1 (Serial1), len 56, sending Jan 20 16:10:45.991: ICMP type=3, code=1 Router1 correctly sent its packets to Router2, but Router2 does not know how to access address 172.16.4.34. Router2 sends back an "unreachable ICMP" message to Router1. Enable Routing Information Protocol (RIP) on Router2 and Router3: Router2# router rip network 172.16.0.7 network 10.0.7.23 Router3# router rip network 10.0.7.23 network 172.16.0.34 Results: Router1#debug ip packet IP packet debugging is on Router1#ping 172.16.4.34 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.4.34, timeout is 2 seconds: Jan 20 16:16:13.367: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending. Jan 20 16:16:15.363: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending. Jan 20 16:16:17.363: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending. Jan 20 16:16:19.363: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending. Jan 20 16:16:21.363: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending. Success rate is 0 percent (0/5) Router1 sends packets to Router4, but Router4 does not send an answer back. Possible problem on Router4: Router4#debug ip packet IP packet debugging is on Router4# Jan 20 16:18:45.903: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:18:45.911: IP: s=172.16.4.34 (local), d=172.16.12.1, len 100, unroutable Jan 20 16:18:47.903: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:18:47.907: IP: s=172.16.4.34 (local), d=172.16.12.1, len 100, unroutable Jan 20 16:18:49.903: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:18:49.907: IP: s=172.16.4.34 (local), d=172.16.12.1, len 100, unroutable Jan 20 16:18:51.903: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:18:51.907: IP: s=172.16.4.34 (local), d=172.16.12.1, len 100, unroutable Jan 20 16:18:53.903: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:18:53.907: IP: s=172.16.4.34 (local), d=172.16.12.1, len 100, unroutable Router 4 receives the ICMP packets, and tries to answer to 172.16.12.1, but because it does not have a route to this network, it fails. Add a static route to Router4: Router4(config)#ip route 0.0.0.0 0.0.0.0 Serial0 Now both sides can access each other: Router1#ping 172.16.4.34 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.4.34, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 32/35/36 ms Interface DownThis is a situation where the interface stops no longer works. In this next example is an attempt to ping Router4 from Router1: Router1#ping 172.16.4.34 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.4.34, timeout is 2 seconds: U.U.U Success rate is 0 percent (0/5) Since the routing is correct, do a step-by-step troubleshoot of the issue. Try to ping Router2: Router1#ping 172.16.0.12 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.0.12, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/4 ms From the previous example, the problem is between Router2 and Router3. One possibility is that the serial interface on Router3 has been shut down: Router3#show ip interface brief Serial0 172.16.3.34 YES manual up up Serial1 10.0.3.23 YES manual administratively down down This is simple to fix: Router3#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router3(config)#interface serial1 Router3(config-if)#no shutdown Router3(config-if)# Jan 20 16:20:53.900: %LINK-3-UPDOWN: Interface Serial1, changed state to up Jan 20 16:20:53.910: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to up Access-list CommandIn this scenario, only telnet traffic is allowed to enter Router4 through interface Serial0. Router4(config)# access-list 100 permit tcp any any eq telnet Router4(config)#interface serial0 Router4(config-if)#ip access-group 100 in Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#access-list 100 permit ip host 172.16.12.1 host 172.16.4.34 Router1(config)#access-list 100 permit ip host 172.16.4.34 host 172.16.12.1 Router1(config)#end Router1#debug ip packet 100 IP packet debugging is on Router1#debug ip icmp ICMP packet debugging is on Try to ping Router4: Router1#ping 172.16.4.34 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.4.34, timeout is 2 seconds: U.U.U Success rate is 0 percent (0/5) Jan 20 16:34:49.207: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending Jan 20 16:34:49.287: IP: s=172.16.4.34 (Serial0), d=172.16.12.1 (Serial0), len 56, rcvd 3 Jan 20 16:34:49.291: ICMP: dst (172.16.12.1) administratively prohibited unreachable rcv from 172.16.4.34 Jan 20 16:34:49.295: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending Jan 20 16:34:51.295: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending Jan 20 16:34:51.367: IP: s=172.16.4.34 (Serial0), d=172.16.12.1 (Serial0), len 56, rcvd 3 Jan 20 16:34:51.371: ICMP: dst (172.16.12.1) administratively prohibited unreachable rcv from 172.16.4.34 Jan 20 16:34:51.379: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 100, sending At the end of an access-list command there is always an implicit deny all. This means that the ICMP packets that enter the Serial 0 interface on Router4 are denied, and Router 4 sends an ICMP "administratively prohibited unreachable" message to the source of the original packet as shown in the debug message. The solution is to add this line in the access-list command: Router4(config)#access-list 100 permit icmp any any Address Resolution Protocol (ARP) IssueIn this scenario, this is the Ethernet connection:
Router4#ping 172.16.100.5 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.100.5, timeout is 2 seconds: Jan 20 17:04:05.167: IP: s=172.16.100.4 (local), d=172.16.100.5 (Ethernet0), len 100, sending Jan 20 17:04:05.171: IP: s=172.16.100.4 (local), d=172.16.100.5 (Ethernet0), len 100, encapsulation failed. Jan 20 17:04:07.167: IP: s=172.16.100.4 (local), d=172.16.100.5 (Ethernet0), len 100, sending Jan 20 17:04:07.171: IP: s=172.16.100.4 (local), d=172.16.100.5 (Ethernet0), len 100, encapsulation failed. Jan 20 17:04:09.175: IP: s=172.16.100.4 (local), d=172.16.100.5 (Ethernet0), len 100, sending Jan 20 17:04:09.183: IP: s=172.16.100.4 (local), d=172.16.100.5 (Ethernet0), len 100, encapsulation failed. Jan 20 17:04:11.175: IP: s=172.16.100.4 (local), d=172.16.100.5 (Ethernet0), len 100, sending Jan 20 17:04:11.179: IP: s=172.16.100.4 (local), d=172.16.100.5 (Ethernet0), len 100, encapsulation failed. Jan 20 17:04:13.175: IP: s=172.16.100.4 (local), d=172.16.100.5 (Ethernet0), len 100, sending Jan 20 17:04:13.179: IP: s=172.16.100.4 (local), d=172.16.100.5 (Ethernet0), len 100, encapsulation failed. Success rate is 0 percent (0/5) Router4# In this example, the ping does not work due to "encapsulation failed" message. This means that the router knows on which interface it has to send the packet but does not know how to do it. In this case, you need to understand how the Address Resolution Protocol (ARP) works. ARP is a protocol used to map the Layer 2 address (MAC address) to a Layer 3 address (IP address). You can check this with the show arp command: Router4#show arp Protocol Address Age (min) Hardware Addr Type Interface Internet 172.16.100.4 - 0000.0c5d.7a0d ARPA Ethernet0 Internet 172.16.100.7 10 0060.5cf4.a955 ARPA Ethernet0 Return to the "encapsulation failed" problem, but this time enable the debug arp command: The previous output shows that Router4 broadcasts packets and sends them to the Ethernet broadcast address FFFF.FFFF.FFFF. Here, the 0000.0000.0000 means that Router4 looks for the MAC address of the destination 172.16.100.5. Since it does not know the MAC address while the ARP is requested in this example, it uses 0000.0000.000 as a placeholder in the broadcast frames sent out of interface Ethernet 0 and asks which MAC address corresponds to 172.16.100.5. If there is no answer, the MAC address that corresponds to the IP address in the show arp output is marked as incomplete: Router4#show arp Protocol Address Age (min) Hardware Addr Type Interface Internet 172.16.100.4 - 0000.0c5d.7a0d ARPA Ethernet0 Internet 172.16.100.5 0 Incomplete ARPA Internet 172.16.100.7 2 0060.5cf4.a955 ARPA Ethernet0 After a predetermined period, this incomplete entry is purged from the ARP table. As long as the MAC address is not in the ARP table, the ping fails as a result of "encapsulation failed". DelayBy default, if you do not receive an answer from the remote end within two seconds, the ping fails: Router1#ping 172.16.0.12 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.0.12, timeout is 2 seconds: ..... Success rate is 0 percent (0/5) On networks with a slow link or a long delay, two seconds are not enough. You can change this default with an extended ping: Router1#ping Protocol [ip]: Target IP address: 172.16.0.12 Repeat count [5]: Datagram size [100]: Timeout in seconds [2]: 30 Extended commands [n]: Sweep range of sizes [n]: Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.0.12, timeout is 30 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1458/2390/6066 ms For more information on the extended ping command, see Understand the Extended Ping and Extended Traceroute Commands . In the previous example, when the timeout was increased the ping was successful. Note: The average round-trip time is more than two seconds. Correct Source AddressThis example is a common scenario:
Add a LAN interface on Router1: Router1(config)#interface ethernet0 Router1(config-if)#ip address 10.0.0.1 255.255.255.0 From a station on the LAN, you can ping Router1. From Router1 you can ping Router2. But from a station on the LAN, you cannot ping Router2. From Router1, you can ping Router2 because, by default, you use the IP address of the outgoing interface as the source address in your ICMP packet. Router2 does not have information about this new LAN. If it has to reply to a packet from this network, it does not know how to handle it. Router1#debug ip packet IP packet debugging is on Warning: When the debug ip packet command is used on a production router it can cause high CPU utilization. This can result in a severe performance degradation or a network outage. Router1#ping 172.16.0.12 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.0.12, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 4/7/9 ms Router1# Jan 20 16:35:54.227: IP: s=172.16.12.1 (local), d=172.16.0.12 (Serial0), len 100, sending Jan 20 16:35:54.259: IP: s=172.16.0.12 (Serial0), d=172.16.12.1 (Serial0), len 100, rcvd 3 The previous output example works because the source address of the packet sent is 172.16.12.1. To simulate a packet from the LAN, you need to use an extended ping: Router1#ping Protocol [ip]: Target IP address: 172.16.0.12 Repeat count [5]: Datagram size [100]: Timeout in seconds [2]: Extended commands [n]: y Source address or interface: 10.0.0.1 Type of service [0]: Set DF bit in IP header? [no]: Validate reply data? [no]: Data pattern [0xABCD]: Loose, Strict, Record, Timestamp, Verbose[none]: Sweep range of sizes [n]: Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.0.12, timeout is 2 seconds: Jan 20 16:40:18.303: IP: s=10.0.0.1 (local), d=172.16.0.12 (Serial0), len 100, sending. Jan 20 16:40:20.303: IP: s=10.0.0.1 (local), d=172.16.0.12 (Serial0), len 100, sending. Jan 20 16:40:22.303: IP: s=10.0.0.1 (local), d=172.16.0.12 (Serial0), len 100, sending. Jan 20 16:40:24.303: IP: s=10.0.0.1 (local), d=172.16.0.12 (Serial0), len 100, sending Jan 20 16:40:26.303: IP: s=10.0.0.1 (local), d=172.16.0.12 (Serial0), len 100, sending. Success rate is 0 percent (0/5) This time, the source address is 10.0.0.1, and it does not work. Packets are sent but no response is received. To fix this issue, add a route to 10.0.0.0 in Router2. The basic rule is that the pinged device must also know how to send the reply to the source of the ping. High Input Queue DropsWhen a packet enters the router, the router attempts to forward it at interrupt level. If a match cannot be found in an appropriate cache table, the packet is queued in the input queue of the incoming interface to be processed. Some packets are always processed, but with the appropriate configuration and in stable networks, the rate of processed packets must never congest the input queue. If the input queue is full, the packet is dropped. Though the interface is up, and you cannot ping the device due to high input queue drops. You can check the input drops with the show interface command. As seen from the output, Input Queue Drop is high. Refer to Troubleshoot Input Queue Drops and Output Queue Drops to troubleshoot Input/Output queue drops. The Traceroute CommandThe traceroute command is used to discover the routes that packets actually take when they travel to their destination. The device (for example, a router or a PC) sends out a sequence of User Datagram Protocol (UDP) datagrams to an invalid port address at the remote host. Three datagrams are sent, each with a Time-To-Live (TTL) field value set to one. The TTL value of 1 causes the datagram to "timeout" as soon as it hits the first router in the path; this router then responds with an ICMP Time Exceeded Message (TEM) that indicates that the datagram has expired. Another three UDP messages are now sent, each with the TTL value set to 2, which causes the second router to return ICMP TEMs. This process continues until the packets actually reach the other destination. Since these datagrams try to access an invalid port at the destination host, ICMP Port Unreachable Messages are returned, and indicates an unreachable port; this event signals the Traceroute program that it is finished. The purpose behind this is to record the source of each ICMP Time Exceeded Message to provide a trace of the path the packet took to reach the destination. Router1#traceroute 172.16.4.34 Type escape sequence to abort. Tracing the route to 172.16.4.34 1 172.16.0.12 4 msec 4 msec 4 msec 2 10.0.3.23 20 msec 16 msec 16 msec 3 172.16.4.34 16 msec * 16 msec Jan 20 16:42:48.611: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 28, sending Jan 20 16:42:48.615: UDP src=39911, dst=33434 Jan 20 16:42:48.635: IP: s=172.16.0.12 (Serial0), d=172.16.12.1 (Serial0), len 56, rcvd 3 Jan 20 16:42:48.639: ICMP type=11, code=0 !--- ICMP Time Exceeded Message from Router2. Jan 20 16:42:48.643: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 28, sending Jan 20 16:42:48.647: UDP src=34237, dst=33435 Jan 20 16:42:48.667: IP: s=172.16.0.12 (Serial0), d=172.16.12.1 (Serial0), len 56, rcvd 3 Jan 20 16:42:48.671: ICMP type=11, code=0 Jan 20 16:42:48.675: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 28, sending Jan 20 16:42:48.679: UDP src=33420, dst=33436 Jan 20 16:42:48.699: IP: s=172.16.0.12 (Serial0), d=172.16.12.1 (Serial0), len 56, rcvd 3 Jan 20 16:42:48.703: ICMP type=11, code=0 This is the first sequence of packets is sent with a TTL=1. The first router, in this case Router2 (172.16.0.12), drops the packet, and sends back to the source (172.16.12.1) a type=11 ICMP message. This corresponds to the Time Exceeded Message. Jan 20 16:42:48.707: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 28, sending Jan 20 16:42:48.711: UDP src=35734, dst=33437 Jan 20 16:42:48.743: IP: s=10.0.3.23 (Serial0), d=172.16.12.1 (Serial0), len 56, rcvd 3 Jan 20 16:42:48.747: ICMP type=11, code=0 !--- ICMP Time Exceeded Message from Router3. Jan 20 16:42:48.751: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 28, sending Jan 20 16:42:48.755: UDP src=36753, dst=33438 Jan 20 16:42:48.787: IP: s=10.0.3.23 (Serial0), d=172.16.12.1 (Serial0), len 56, rcvd 3 Jan 20 16:42:48.791: ICMP type=11, code=0 Jan 20 16:42:48.795: IP: s=172.16.12.1 (local), d=172.16.4.34 (Serial0), len 28, sending Jan 20 16:42:48.799: UDP src=36561, dst=33439 Jan 20 16:42:48.827: IP: s=10.0.3.23 (Serial0), d=172.16.12.1 (Serial0), len 56, rcvd 3 Jan 20 16:42:48.831: ICMP type=11, code=0 The same process occurs for Router3 (10.0.3.23) with a TTL=2: With a TTL=3, Router4 is finally reached. This time, since the port is not valid, Router4 sends back to Router1 an ICMP message with type=3, a Destination Unreachable Message, and code=3 meaning port unreachable. The next table lists the characters that can appear in the traceroute command output. IP Traceroute Text Characters
PerformanceYou can obtain the round-trip time (RTT) with the ping and traceroute commands. This is the time required to send an echo packet and get an answer back. This can provide a rough idea of the delay on the link. However, these figures are not precise enough to be used for performance evaluation. When a packet destination is the router itself, this packet has to be process-switched. The processor has to handle the information from this packet and send an answer back. This is not the main goal of a router. By definition, a router is built to route packets. An answered ping is offered as a best-effort service. To illustrate this, this is an example of a ping from Router1 to Router2: Router1#ping 172.16.0.12 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.0.12, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/4 ms The RTT is approximately four milliseconds. After you enable some process-intensive features on Router2, try to ping Router2 from Router1. Router1#ping 172.16.0.12 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.0.12, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 24/25/28 ms The RTT has dramatically increased here. Router2 is quite busy, and the priority is not to answer the ping. A better way to test router performance is with traffic that goes through the router.
The traffic is then fast-switched and is handled by the router with the highest priority. The basic network illustrates this:
Ping Router3 from Router1: Router1#ping 10.0.3.23 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.0.3.23, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 32/32/32 ms The traffic goes through Router2 and is now fast-switched. Enable the process-intensive feature on Router2: Router1#ping 10.0.3.23 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.0.3.23, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 32/32/36 ms There is almost no difference. This is because, on Router2, the packets are now handled at interrupt level. Use the Debug CommandBefore you use debug commands, refer to Important Information on Debug Commands . The different debug commands used in this article shows what happens when a ping or traceroute command is used. These commands can help you troubleshoot issues. However, in a production environment, debugs must be used with caution. If your CPU is not powerful, or if you have a lot of process-switched packets, they can easily stall your device. There are a couple of ways to minimize the impact of the debug command on the router. One way is to use access lists to narrow down the specific traffic that you want to monitor. Here is an example: With this configuration, Router4 only prints the debug message that matches the access-list 150. A ping from Router1 causes this message to display: Router4# Jan 20 16:51:16.911: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:51:17.003: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:51:17.095: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:51:17.187: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:51:17.279: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 The answer to the problem does not come from Router4 because these packets do not match the access-list. To see them, add: Router4(config)#access-list 150 permit ip host 172.16.12.1 host 172.16.4.34 Router4(config)#access-list 150 permit ip host 172.16.4.34 host 172.16.12.1 Results: Jan 20 16:53:16.527: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:53:16.531: IP: s=172.16.4.34 (local), d=172.16.12.1 (Serial0), len 100, sending Jan 20 16:53:16.627: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:53:16.635: IP: s=172.16.4.34 (local), d=172.16.12.1 (Serial0), len 100, sending Jan 20 16:53:16.727: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:53:16.731: IP: s=172.16.4.34 (local), d=172.16.12.1 (Serial0), len 100, sending Jan 20 16:53:16.823: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:53:16.827: IP: s=172.16.4.34 (local), d=172.16.12.1 (Serial0), len 100, sending Jan 20 16:53:16.919: IP: s=172.16.12.1 (Serial0), d=172.16.4.34 (Serial0), len 100, rcvd 3 Jan 20 16:53:16.923: IP: s=172.16.4.34 (local), d=172.16.12.1 (Serial0), len 100, sending Another way to lower the impact of the debug command is to buffer the debug messages and display them with the show log command once the debug has been turned off: The ping and traceroute commands are helpful utilities that you can use to troubleshoot network access problems. They are also very easy to use. These two commands are the widely used by network engineers. Related Information
Which of the following is the Windows command that can display a list of the source and destination IP addresses for a PC's existing connections?The "netstat" command can be used to display a variety of information about IP-based connections on a PC. For example, you can view information about current sessions, including source and destination IP addresses and port numbers.
What command can be used on Windows PC to see the IP configuration of the computer?First, click on your Start Menu and type cmd in the search box and press enter. A black and white window will open where you will type ipconfig /all and press enter. There is a space between the command ipconfig and the switch of /all. Your ip address will be the IPv4 address.
What command can be used on a Windows PC to see the IP configuration of that computer show interfaces ping show IP interface brief ipconfig?The ipconfig command displays the basic IP addressing information for each network interface on the Windows system. This information includes both the IP address and subnet mask.
What is the command to see the list of connected devices?Enter the net view command to view devices connected to your network You will then see a list of devices connected to your network in the output. To view the IP addresses of the devices, enter the arp -a command, which will list the Internet address physical address and type of each device.
|
Which of the following is the Windows command that can display a list of the source and destination IP addresses for a PCs existing connections?
zusammenhängende Posts
Urheberrechte © © 2024 decemle Inc.
