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What does a ping result of "Destination unreachable" and "Host unreachable" mean?

asked 2023-09-14 17:52:11 +0000

Victrix gravatar image

updated 2023-09-14 19:28:19 +0000

Guy Harris gravatar image

hey everyone,

I am new here, and I am not an wireshark expert, I met this problem, our site became inreachable, when I ping I got this message using wireshark.

Internet Protocol Version 4, **Src: SITE IP**, **Dst: MY LAPTOP**

Internet Control Message Protocol
Type: 3 (Destination unreachable)
Code: 1 (Host unreachable)
Checksum: 0x7513 [correct]
[Checksum Status: Good]
Unused: 00000000
Internet Protocol Version 4, **Src: MY LAPTOP, Dst: SITE IP**
    0100 .... = Version: 4
    .... 0101 = Header Length: 20 bytes (5)
    Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
        0000 00.. = Differentiated Services Codepoint: Default (0)
        .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    Total Length: 60
    Identification: 0x8e7f (36479)
    000. .... = Flags: 0x0
    ...0 0000 0000 0000 = Fragment Offset: 0
    Time to Live: 110
    Protocol: ICMP (1)
    Header Checksum: 0x16b6 [validation disabled]
    [Header checksum status: Unverified]
    Source Address: MY LAPTOP
    Destination Address: SITE IP
Internet Control Message Protocol

THANKS

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answered 2023-09-15 06:43:09 +0000

SYN-bit gravatar image

ICMP type 3, code 1 messages (Host Unreachable) are usually sent by the router that has an interface in the subnet of the host you are trying to reach when that host does not respond to the ARP request sent by that router. This means the host is not available on the subnet. I.e. it is unreachable.

If the source IP address of the ICMP host unreachable message is the same as the destination of the initial packet (both are listed as "SITE IP" in your output), then maybe there is a loadbalancer involved that chooses to send the unreachable this way, but it might also have other reasons.

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answered 2023-09-15 06:28:33 +0000

BigFatCat gravatar image

RFC 1812 provides an explanation.

1 = Host Unreachable - generated by a router if a forwarding path (route) to the destination host on a directly connected network is not available (does not respond to ARP);

RFC 1812 PAGE 81

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Asked: 2023-09-14 17:52:11 +0000

Seen: 2,598 times

Last updated: Sep 15 '23