Ping Question

R2 doesn't have a route to network 3.3.3.0/24 but it sends a host unreachable to R1 instead of network unreachable...

Regards,
Krik

Is there any logical explanation for why the host unreachable error message is sent instead of network unreachable message?

Here is my explanation,why R2 should send an ICMP Network Unreachable.

R2, when it examines the destination IP of 3.3.3.3/24 figures out the host is on 3.3.3.0/24 network. R2 looks at the routing table and finds no route to reach the 3.3.3.0/24 network.

R2 should then send an ICMP network unreachable error message to R1.

If someone can explain, why I am wrong to say the error message should be network unreachable and NOT host unreachable in this scenario, it would be greatly appreciated.

Cheers
FallenZer0

If someone can explain, why I am wrong to say the error message should be network unreachable and NOT host unreachable in this scenario, it would be greatly appreciated.

In both cases, as far as I know, a ping echo reply should not have been sent to the host which is contrary to what GTM is observing.

Hi Folks,

Just some quick thought, (they may have already been mentioned and if so I apologies )

If you are pinging from inside an organisation, you will need to go through a router to get to the "outside world". Now, if this is the case, some sites may be "blocked" ie the router doesn't know how to get to that site. If that is the case, then you will not get a reply, or get the reply you are getting. I think what is means is that although replies are being received, the router doesn't know who is sending them. Does that make any sense, or can someone tell me I'm talking rubbish

Cheers

Rockape

Thanks for the replys guys things are looking a bit clearer for me.Having read your comments it brings me to another question though..

Presuming these replys are coming from the router who has not got the route to the site in its routing table then what makes the difference with the results why do some give you the msg "packets sent 4 recieved 4" but still destination host unreachable and the other tell you "packets sent 4 recieved 0"

Hope you understand what im getting at..

Thanks for the replys guys things are looking a bit clearer for me.Having read your comments it brings me to another question though..

Presuming these replys are coming from the router who has not got the route to the site in its routing table then what makes the difference with the results why do some give you the msg "packets sent 4 recieved 4" but still destination host unreachable and the other tell you "packets sent 4 recieved 0"

Hope you understand what im getting at..

Now things are more clear.

I Think this is the case, When a router does not find an entry in the routing table to route the packet, it drops it and sends a "Destination Host Unreachable" packet to the sender. This packet "as it appears" is counted as 1 recieved packet, hence the 4 sent 4 RECIEVED.

However, when a router finds a routing table entry, it sends the packets to that network but the recieving host itself might not reply (because its firewalled or it doesn't exist), here is when you'll get "Request timed out." message. There is simply no recieved packets at all.

Gotcha thanks a lot for clearing that up for me and thanks again to everyone else who put in a comment or two.