What do PING results actually mean..?

  • Article

My buddy Brett came across this and I thought I would share it!

Here are some useful pointers on the ICMP errors – this helps decipher whether the problem lies in:

  • DNS \ Name resolution
  • Network issue
     

The key (common ones) are in bold

Also remember, a Request Timed Out could mean two things:

  • A packet could get to the destination Host, but from the destination hosts point of view, there was no valid network route back (more on this in #3)
  • A Network loop
Code Value Meaning
0 - Network Unreachable Sent by an IP router when a route for the destination IP address cannot be found in the routing table. The source IP address of this message identifies the router that could not find a route. This message is largely obsolete in today's classless Internet due to the inability of the router to determine the network ID of the destination.
1 - Host Unreachable Sent by an IP router when a route to the destination was not found in the routing table. In today's classless Internet, this is the more appropriate message to send when a router cannot determine the next hop for an IP datagram. This message's source IP address identifies the router that could not deliver the datagram to the destination host.
2 - Protocol Unreachable Sent by the destination host when the Protocol field in the datagram's IP header does not match a client protocol of IP that is being used by the destination. For example, if a host is sent an Open Shortest Path First (OSPF) packet (IP protocol 89), it sends a Protocol Unreachable message back to the sender.
3 - Port Unreachable ;Sent by the destination host when the destination port in the UDP or TCP header does not match an application running on the destination. In practice, however, when TCP ports cannot be found, TCP sends a Connection Reset segment. Therefore, Port Unreachable messages are sent only for UDP messages.
4 - Fragmentation Needed And DF Set Sent by an IP router when fragmentation is needed to forward the IP datagram but the Don't Fragment (DF) flag is set in the IP header. The Fragmentation Needed And DF Set message is an important part of the Path Maximum Transmission Unit (PMTU) Discovery process discussed in the "PMTU Discovery" section of this chapter. This message's source IP address identifies the router that could not fragment the IP datagram.
5 - Source Route Failed Sent by an IP router when it cannot forward an IP datagram using information stored in the Source Route option in the IP header. For example, this ICMP Destination Unreachable message is sent if the sending host is using a strict source route and the next router is not directly reachable. The Source Route Failed message contains source route options of the same type as the offending datagram and includes the path back to the sending host. This message's source IP address identifies the router that could not forward the source-routed IP datagram.
6 - Destination Network Unknown Sent by an IP router when the destination network for the destination IP address is indicated in the routing table as an unknown network. In practice, the Destination Network Unknown message is obsolete; IP routers send a Host Unreachable message instead. <
7 - Destination Host Unknown Sent by an IP router when the destination host does not exist as detected through Network Interface Layer mechanisms. In practice, the Destination Host Unknown message is sent only when the router cannot deliver to a host that is connected to the router by a point-to-point link. This message's source IP address identifies the router that could not deliver the IP datagram.
8 - Source Host Isolated An obsolete message sent by an IP router when it can detect that the source host is isolated from the rest of the network. <
9 - Communication with Destination Network Administratively Prohibited Sent by an IP router when a route to the destination IP address was found but the router cannot forward the IP datagram because of a prohibitive network policy. This message's source IP address identifies the router that could not forward the IP datagram.
10 - Communication with Destination Host Administratively Prohibited Sent by an IP router when it cannot deliver to the destination host because of a prohibitive network policy. This message's source IP address identifies the router that could not deliver the IP datagram.
11 - Network Unreachable for Type of Service Sent by an IP router when a route to the destination IP address for the Type Of Service (TOS) indicated in the IP header of the IP datagram was not found. Only routers that use the TOS field when forwarding IP datagrams send this message. This message's source IP address identifies the router that could not forward the IP datagram.
12 - Host Unreachable for Type of Service Sent by an IP router when it cannot deliver to the destination host for the TOS indicated in the IP header of the IP datagram. Only routers that use the TOS field when forwarding IP datagrams send this message. This message's source IP address identifies the router that could not forward the IP datagram.
13 - Communication Administratively Prohibited Because of Firewalls Sent by an IP router when it cannot forward or deliver the IP datagram because of administratively configured packet filters on the router. This message's source IP address identifies the router that could not forward or deliver the IP datagram.