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I have two Ethernet devices:

  • One is 10.1.1.10 with a netmask set to 255.0.0.0
  • The other is 10.255.253.5 with a netmask set to 255.255.255.0

Why can't I reach the second device from the first one (Even if the devices are directly connected by Ethernet one to the other) ?

I got a time out if I try to ping 10.255.253.5. Only ARP works.

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  • 1
    Are you sure you mean "why can I reach" and not "why can't"? The rest of the wording of your question (and the likely reality) suggests the latter...
    – Mintra
    Apr 18, 2023 at 12:56
  • You are right ! I've updated my question. Sorry about taht
    – Manitoba
    Apr 18, 2023 at 15:00

2 Answers 2

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I got a time out if I try to ping 10.255.253.5. Only ARP works.

That is to be expected. When 10.1.1.10/8 tries to ping 10.255.253.5, it expects it to be "on link" = sharing the same broadcast domain. It ARPs the destination, succeeds and send an ICMP echo request.

The echo request is received by 10.255.253.5/24, but trying to send the echo reply it requires a gateway in between - 10.1.1.10 is not part of 10.255.253.0/24. Failing that, the reply cannot be sent and the ping times out.

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  • Thanks for your precise message. I understand now !
    – Manitoba
    Apr 18, 2023 at 15:01
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Remember that IP addresses are always unique. The host 10.255.253.5 is configured with a /24 subnet mask, which means it sees 10.1.1.10 as on a different subnet. You need a router to route between subnets.

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