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We know that private IP addresses ranges of class A, class B, class C are 10.0.0.0-10.0.0.255, 172.16.0.0-172.16.255.255, 192.168.0.0-192.168.255.255 respectively.

My first questions is that first and last IP address of any class could be used as private net-id, DBA(directed broadcast address) respectively of that entire class? For example 10.0.0.0,10.0.0.255 could we assign for any device? Or are they reserved?

If we use 10.0.0.2 as S. I. P and 10.0.0.13 as D. I. P then it's the unicast packet within the network. My second question is if we use D. I. P as 10.255.255.255 then it will work?

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    Network classes are dead (please let them rest in peace), killed in 1993 (two years before the commercial Internet) by RFCs 1517, 1518, and 1519, which defined CIDR (Classless Inter-Domain Routing). We have not had network classes in this century. Also, directed broadcast is disabled on routers by default.
    – Ron Maupin
    Jan 9, 2022 at 6:00
  • @RonMaupin if 2 router sharing same ip address then packet will go which router if the destination is that ip address?
    – S. M.
    Jan 21, 2022 at 21:23
  • Two hosts on the same network (routers are hosts, too) will cause duplicate address problems. That is an error that needs to be corrected. We have things like FHRPs (HSRP, VRRP, etc.) to allow you to use a single router address for multiple routers, but each router actually has it own, separate address, sharing a virtual address, and the FHRP picks the active router.
    – Ron Maupin
    Jan 21, 2022 at 21:27
  • @RonMaupin if both router are active then which one will be chosen?
    – S. M.
    Jan 21, 2022 at 21:30
  • The FHRP picks the active router. It is based on things like the priority assigned when configuring the FHRP on the routers. There will be a rule for breaking a tie.
    – Ron Maupin
    Jan 21, 2022 at 21:32

2 Answers 2

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Sending a packet to the network broadcast address on the same network is not a directed broadcast as it does not involve a router to direct the broadcast. It is simply a network broadcast. If your network is 10.0.0.0/8, then sending to 10.255.255.255 from any address in that network is a simple network broadcast.

If your network is 10.0.0.0/24, then sending to 10.255.255.255 is a unicast packet to a different network sent to your router that will attempt to forward it toward the destination network. Unless the destination router is configured to forward directed broadcasts (disabled by default), the destination router will drop it.

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  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Ron Maupin
    Jan 9, 2022 at 15:35
  • if one router has IP address 10.0.0.1/24 which connected to two another routers of different networks 10.255.3.1/16 and 10.2.3.1/8. Then if 10.0.0.1/24 use destination address as 10.255.255.255 then it unicasts to both 10.255.3.1/16 and 10.2.3.1/8?
    – S. M.
    Jan 9, 2022 at 16:45
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    No, those are overlapping networks that conflict. routers cannot have overlapping networks. If a router has no path, even a default route, toward a destination, it drops the packet as undeliverable. Remember that ever IPv4 network is a subnet of 0.0.0.0/0. Also, understand that broadcasting is going away in favor of multicasting. Even IPv6 has eliminated broadcast.
    – Ron Maupin
    Jan 9, 2022 at 16:50
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    If the networks overlap, they will conflict. Routers route packets between networks, not from a network back to the same network, so router interfaces must be in different, non-overlapping networks. Routing is deterministic, and routers cannot guess where to send a pascket. If a routing table has two paths toward a destination, it uses the longest match and other methods to break a tie.
    – Ron Maupin
    Jan 9, 2022 at 16:57
  • once again your legendary answer and valuable comments. I am very lucky to have teacher like you.
    – S. M.
    Jan 9, 2022 at 17:02
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It should also be noted, the all-zeros and all-ones addresses of a subnet are the network and broadcast addresses, respectively. Both are reserved and cannot be assigned to a host. In your example 10.0.0.0/24 and 10.0.0.255/24 are reserved addresses. (10.0.0.255/8 is just another host.)

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