How can ping know if my host is down
When I ping
a server there are two kinds of result I might get:
- Timeout
- Host is down message
How does the ping
command know if a host is down? In both cases, the host does not send any response to the ping packet, so how can ping
tell the difference?
ping
add a comment |
When I ping
a server there are two kinds of result I might get:
- Timeout
- Host is down message
How does the ping
command know if a host is down? In both cases, the host does not send any response to the ping packet, so how can ping
tell the difference?
ping
add a comment |
When I ping
a server there are two kinds of result I might get:
- Timeout
- Host is down message
How does the ping
command know if a host is down? In both cases, the host does not send any response to the ping packet, so how can ping
tell the difference?
ping
When I ping
a server there are two kinds of result I might get:
- Timeout
- Host is down message
How does the ping
command know if a host is down? In both cases, the host does not send any response to the ping packet, so how can ping
tell the difference?
ping
ping
edited yesterday
Mark Amery
2951219
2951219
asked yesterday
Bob5421Bob5421
17117
17117
add a comment |
add a comment |
3 Answers
3
active
oldest
votes
Host is down message:
This indicates that you don't know a route to the desired destination, or a remote router reports that it has no route to the destination.
Timeout:
Indicates the absense of Echo Reply messages. No package were received within the default time.
New contributor
add a comment |
Differences between responses are not actually determined by ICMP itself but rather indirectly.
ICMP can distingush between the following:
0 = net unreachable;
1 = host unreachable;
2 = protocol unreachable;
3 = port unreachable;
4 = fragmentation needed and DF set;
5 = source route failed.
But it does so with other network resources. Codes 0, 1, 4, and 5 may be received from a gateway. Codes 2 and 3 may be received from a host.
If, according to the information in the gateway's routing tables, destination network is unreachable, (e.g., the distance to the network is infinity), the gateway may send a destination unreachable message to the internet source host of the datagram. In addition, in some networks, the gateway may be able to determine if the internet destination host is unreachable. It is the Gateways in these networks that can send destination unreachable messages to the source host when the destination host is unreachable, so it's not actually ICMP doing the determinations.
In the case that in the destination host, the IP module cannot deliver the datagram because the indicated protocol module or process port is not active, then the destination host may send a 'destination unreachable' message to the source host.
Finally, if a datagram must be fragmented to be forwarded by a gateway yet the 'Do not Fragment' flag is on, the gateway will discard the datagram and will return a 'destination unreachable' message.
Now to difference between the 2 separate cases: Request Timed Out means that no Echo Reply messages were received within the set time. This can be due to many different causes: ARP request failure, network congestion, packet filtering, routing error, or a even silent discard.
When you get a Reply From [IP address]: 'Destination Host Unreachable,' then the problem occurred at/after a remote router, whose address is indicated by the [IP address]. So it's a router telling you that there is a problem between it and the destination address.
3
no router or other device needs to be involved. Both Windows and Linux produce "host unreachable" if the host is in a local subnet and there is no ARP entry.
– Oh My Goodness
yesterday
If a host is unreachable it cannot produce a receivable-by-initiator answer.
– Overmind
17 hours ago
The pinging host produces the message. Obviously the destination cannot.
– Oh My Goodness
17 hours ago
That comes form the gateway.
– Overmind
17 hours ago
No. "Gateway" is a layer 3 construct. There is no routing, and thus no gateway involved at all when pinging a host on the local subnet.
– Oh My Goodness
17 hours ago
|
show 10 more comments
You cant ping if the computer isnt connected to the internet because by pinging you actually request the ip of the host .
New contributor
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
Host is down message:
This indicates that you don't know a route to the desired destination, or a remote router reports that it has no route to the destination.
Timeout:
Indicates the absense of Echo Reply messages. No package were received within the default time.
New contributor
add a comment |
Host is down message:
This indicates that you don't know a route to the desired destination, or a remote router reports that it has no route to the destination.
Timeout:
Indicates the absense of Echo Reply messages. No package were received within the default time.
New contributor
add a comment |
Host is down message:
This indicates that you don't know a route to the desired destination, or a remote router reports that it has no route to the destination.
Timeout:
Indicates the absense of Echo Reply messages. No package were received within the default time.
New contributor
Host is down message:
This indicates that you don't know a route to the desired destination, or a remote router reports that it has no route to the destination.
Timeout:
Indicates the absense of Echo Reply messages. No package were received within the default time.
New contributor
New contributor
answered yesterday
SantiCartaSantiCarta
263
263
New contributor
New contributor
add a comment |
add a comment |
Differences between responses are not actually determined by ICMP itself but rather indirectly.
ICMP can distingush between the following:
0 = net unreachable;
1 = host unreachable;
2 = protocol unreachable;
3 = port unreachable;
4 = fragmentation needed and DF set;
5 = source route failed.
But it does so with other network resources. Codes 0, 1, 4, and 5 may be received from a gateway. Codes 2 and 3 may be received from a host.
If, according to the information in the gateway's routing tables, destination network is unreachable, (e.g., the distance to the network is infinity), the gateway may send a destination unreachable message to the internet source host of the datagram. In addition, in some networks, the gateway may be able to determine if the internet destination host is unreachable. It is the Gateways in these networks that can send destination unreachable messages to the source host when the destination host is unreachable, so it's not actually ICMP doing the determinations.
In the case that in the destination host, the IP module cannot deliver the datagram because the indicated protocol module or process port is not active, then the destination host may send a 'destination unreachable' message to the source host.
Finally, if a datagram must be fragmented to be forwarded by a gateway yet the 'Do not Fragment' flag is on, the gateway will discard the datagram and will return a 'destination unreachable' message.
Now to difference between the 2 separate cases: Request Timed Out means that no Echo Reply messages were received within the set time. This can be due to many different causes: ARP request failure, network congestion, packet filtering, routing error, or a even silent discard.
When you get a Reply From [IP address]: 'Destination Host Unreachable,' then the problem occurred at/after a remote router, whose address is indicated by the [IP address]. So it's a router telling you that there is a problem between it and the destination address.
3
no router or other device needs to be involved. Both Windows and Linux produce "host unreachable" if the host is in a local subnet and there is no ARP entry.
– Oh My Goodness
yesterday
If a host is unreachable it cannot produce a receivable-by-initiator answer.
– Overmind
17 hours ago
The pinging host produces the message. Obviously the destination cannot.
– Oh My Goodness
17 hours ago
That comes form the gateway.
– Overmind
17 hours ago
No. "Gateway" is a layer 3 construct. There is no routing, and thus no gateway involved at all when pinging a host on the local subnet.
– Oh My Goodness
17 hours ago
|
show 10 more comments
Differences between responses are not actually determined by ICMP itself but rather indirectly.
ICMP can distingush between the following:
0 = net unreachable;
1 = host unreachable;
2 = protocol unreachable;
3 = port unreachable;
4 = fragmentation needed and DF set;
5 = source route failed.
But it does so with other network resources. Codes 0, 1, 4, and 5 may be received from a gateway. Codes 2 and 3 may be received from a host.
If, according to the information in the gateway's routing tables, destination network is unreachable, (e.g., the distance to the network is infinity), the gateway may send a destination unreachable message to the internet source host of the datagram. In addition, in some networks, the gateway may be able to determine if the internet destination host is unreachable. It is the Gateways in these networks that can send destination unreachable messages to the source host when the destination host is unreachable, so it's not actually ICMP doing the determinations.
In the case that in the destination host, the IP module cannot deliver the datagram because the indicated protocol module or process port is not active, then the destination host may send a 'destination unreachable' message to the source host.
Finally, if a datagram must be fragmented to be forwarded by a gateway yet the 'Do not Fragment' flag is on, the gateway will discard the datagram and will return a 'destination unreachable' message.
Now to difference between the 2 separate cases: Request Timed Out means that no Echo Reply messages were received within the set time. This can be due to many different causes: ARP request failure, network congestion, packet filtering, routing error, or a even silent discard.
When you get a Reply From [IP address]: 'Destination Host Unreachable,' then the problem occurred at/after a remote router, whose address is indicated by the [IP address]. So it's a router telling you that there is a problem between it and the destination address.
3
no router or other device needs to be involved. Both Windows and Linux produce "host unreachable" if the host is in a local subnet and there is no ARP entry.
– Oh My Goodness
yesterday
If a host is unreachable it cannot produce a receivable-by-initiator answer.
– Overmind
17 hours ago
The pinging host produces the message. Obviously the destination cannot.
– Oh My Goodness
17 hours ago
That comes form the gateway.
– Overmind
17 hours ago
No. "Gateway" is a layer 3 construct. There is no routing, and thus no gateway involved at all when pinging a host on the local subnet.
– Oh My Goodness
17 hours ago
|
show 10 more comments
Differences between responses are not actually determined by ICMP itself but rather indirectly.
ICMP can distingush between the following:
0 = net unreachable;
1 = host unreachable;
2 = protocol unreachable;
3 = port unreachable;
4 = fragmentation needed and DF set;
5 = source route failed.
But it does so with other network resources. Codes 0, 1, 4, and 5 may be received from a gateway. Codes 2 and 3 may be received from a host.
If, according to the information in the gateway's routing tables, destination network is unreachable, (e.g., the distance to the network is infinity), the gateway may send a destination unreachable message to the internet source host of the datagram. In addition, in some networks, the gateway may be able to determine if the internet destination host is unreachable. It is the Gateways in these networks that can send destination unreachable messages to the source host when the destination host is unreachable, so it's not actually ICMP doing the determinations.
In the case that in the destination host, the IP module cannot deliver the datagram because the indicated protocol module or process port is not active, then the destination host may send a 'destination unreachable' message to the source host.
Finally, if a datagram must be fragmented to be forwarded by a gateway yet the 'Do not Fragment' flag is on, the gateway will discard the datagram and will return a 'destination unreachable' message.
Now to difference between the 2 separate cases: Request Timed Out means that no Echo Reply messages were received within the set time. This can be due to many different causes: ARP request failure, network congestion, packet filtering, routing error, or a even silent discard.
When you get a Reply From [IP address]: 'Destination Host Unreachable,' then the problem occurred at/after a remote router, whose address is indicated by the [IP address]. So it's a router telling you that there is a problem between it and the destination address.
Differences between responses are not actually determined by ICMP itself but rather indirectly.
ICMP can distingush between the following:
0 = net unreachable;
1 = host unreachable;
2 = protocol unreachable;
3 = port unreachable;
4 = fragmentation needed and DF set;
5 = source route failed.
But it does so with other network resources. Codes 0, 1, 4, and 5 may be received from a gateway. Codes 2 and 3 may be received from a host.
If, according to the information in the gateway's routing tables, destination network is unreachable, (e.g., the distance to the network is infinity), the gateway may send a destination unreachable message to the internet source host of the datagram. In addition, in some networks, the gateway may be able to determine if the internet destination host is unreachable. It is the Gateways in these networks that can send destination unreachable messages to the source host when the destination host is unreachable, so it's not actually ICMP doing the determinations.
In the case that in the destination host, the IP module cannot deliver the datagram because the indicated protocol module or process port is not active, then the destination host may send a 'destination unreachable' message to the source host.
Finally, if a datagram must be fragmented to be forwarded by a gateway yet the 'Do not Fragment' flag is on, the gateway will discard the datagram and will return a 'destination unreachable' message.
Now to difference between the 2 separate cases: Request Timed Out means that no Echo Reply messages were received within the set time. This can be due to many different causes: ARP request failure, network congestion, packet filtering, routing error, or a even silent discard.
When you get a Reply From [IP address]: 'Destination Host Unreachable,' then the problem occurred at/after a remote router, whose address is indicated by the [IP address]. So it's a router telling you that there is a problem between it and the destination address.
answered yesterday
OvermindOvermind
1,193514
1,193514
3
no router or other device needs to be involved. Both Windows and Linux produce "host unreachable" if the host is in a local subnet and there is no ARP entry.
– Oh My Goodness
yesterday
If a host is unreachable it cannot produce a receivable-by-initiator answer.
– Overmind
17 hours ago
The pinging host produces the message. Obviously the destination cannot.
– Oh My Goodness
17 hours ago
That comes form the gateway.
– Overmind
17 hours ago
No. "Gateway" is a layer 3 construct. There is no routing, and thus no gateway involved at all when pinging a host on the local subnet.
– Oh My Goodness
17 hours ago
|
show 10 more comments
3
no router or other device needs to be involved. Both Windows and Linux produce "host unreachable" if the host is in a local subnet and there is no ARP entry.
– Oh My Goodness
yesterday
If a host is unreachable it cannot produce a receivable-by-initiator answer.
– Overmind
17 hours ago
The pinging host produces the message. Obviously the destination cannot.
– Oh My Goodness
17 hours ago
That comes form the gateway.
– Overmind
17 hours ago
No. "Gateway" is a layer 3 construct. There is no routing, and thus no gateway involved at all when pinging a host on the local subnet.
– Oh My Goodness
17 hours ago
3
3
no router or other device needs to be involved. Both Windows and Linux produce "host unreachable" if the host is in a local subnet and there is no ARP entry.
– Oh My Goodness
yesterday
no router or other device needs to be involved. Both Windows and Linux produce "host unreachable" if the host is in a local subnet and there is no ARP entry.
– Oh My Goodness
yesterday
If a host is unreachable it cannot produce a receivable-by-initiator answer.
– Overmind
17 hours ago
If a host is unreachable it cannot produce a receivable-by-initiator answer.
– Overmind
17 hours ago
The pinging host produces the message. Obviously the destination cannot.
– Oh My Goodness
17 hours ago
The pinging host produces the message. Obviously the destination cannot.
– Oh My Goodness
17 hours ago
That comes form the gateway.
– Overmind
17 hours ago
That comes form the gateway.
– Overmind
17 hours ago
No. "Gateway" is a layer 3 construct. There is no routing, and thus no gateway involved at all when pinging a host on the local subnet.
– Oh My Goodness
17 hours ago
No. "Gateway" is a layer 3 construct. There is no routing, and thus no gateway involved at all when pinging a host on the local subnet.
– Oh My Goodness
17 hours ago
|
show 10 more comments
You cant ping if the computer isnt connected to the internet because by pinging you actually request the ip of the host .
New contributor
add a comment |
You cant ping if the computer isnt connected to the internet because by pinging you actually request the ip of the host .
New contributor
add a comment |
You cant ping if the computer isnt connected to the internet because by pinging you actually request the ip of the host .
New contributor
You cant ping if the computer isnt connected to the internet because by pinging you actually request the ip of the host .
New contributor
New contributor
answered 12 hours ago
AltairAltair
1
1
New contributor
New contributor
add a comment |
add a comment |
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