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ICMP: Ping and Trace

Q: Are pings forwarded by routers? A: Yes! This is why you can ping devices all over the Internet. Q: Do all devices forward or respond to pings? A: No, this is up to the network administrator of the device. Devices, including routers, can be configured not to reply to pings (ICMP echo requests). This is why you may not always be able to ping a device. Also, routers can be configured not to forward pings destined for other devices. | ICMP: Ping and Trace 172.30.1.20 172.30.1.25 Ping Uses ICMP message encapsulated within an IP Packet Protocol field = 1 Both are layer 3 protocols. (ICMP is considered as a network layer protocol.) Does not use TCP or UDP, but may be acted upon by the receiver using TCP or UDP. Format ping ip address (or ping for extended ping) ping 172.30.1.25 Echo Request The sender of the ping, transmits an ICMP message, “Echo Request” Echo Request - Within ICMP Message Type = 8 Code = 0 172.30.1.20 172.30.1.25 Echo Reply The IP address (destination) of the ping, receives the ICMP message, “Echo Request” The ip address (destination) of the ping, returns the ICMP message, “Echo Reply” Echo Reply - Within ICMP Message Type = 0 Code = 0 Q: Are pings forwarded by routers? A: Yes! This is why you can ping devices all over the Internet. Q: Do all devices forward or respond to pings? A: No, this is up to the network administrator of the device. Devices, including routers, can be . | ICMP: Ping and Trace 172.30.1.20 172.30.1.25 Ping Uses ICMP message encapsulated within an IP Packet Protocol field = 1 Both are layer 3 protocols. (ICMP is considered as a network layer protocol.) Does not use TCP or UDP, but may be acted upon by the receiver using TCP or UDP. Format ping ip address (or ping for extended ping) ping 172.30.1.25 Echo Request The sender of the ping, transmits an ICMP message, “Echo Request” Echo Request - Within ICMP Message Type = 8 Code = 0 172.30.1.20 172.30.1.25 Echo Reply The IP address (destination) of the ping, receives the ICMP message, “Echo Request” The ip address (destination) of the ping, returns the ICMP message, “Echo Reply” Echo Reply - Within ICMP Message Type = 0 Code = 0 Q: Are pings forwarded by routers? A: Yes! This is why you can ping devices all over the Internet. Q: Do all devices forward or respond to pings? A: No, this is up to the network administrator of the device. Devices, including routers, can be configured not to reply to pings (ICMP echo requests). This is why you may not always be able to ping a device. Also, routers can be configured not to forward pings destined for other devices. Routers and Pings Traceroute Traceroute is a utility that records the route (router IP addresses) between two devices on different networks. Tracroute http://en.wikipedia.org/wiki/Traceroute On modern Unix and Linux-based operating systems, the traceroute utility by default uses UDP datagrams with a destination port number starting at 33434. The traceroute utility usually has an option to specify use of ICMP echo request (type 8) instead. The Windows utility uses ICMP echo request, better known as ping packets. Some firewalls on the path being investigated may block UDP probes but allow the ICMP echo request traffic to pass through. There are also traceroute implementations sending out TCP packets, such as tcptraceroute or Layer Four Trace. In Microsoft Windows, traceroute is named .