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Scenario:1

Suppose external Router R1 has interface a connected with interface b of the site Router R2. And Router R1 using IP address 80.0.0.0/8 for a. Router R2 has 4 subnets 80.0.0.0/10, 80.64.0.0/10, 80.128.0.0/10, 80.192.0.0/10. enter image description here My first question is router R1 with interface a and router R2 interface b has same ip address 80.0.0.0/8 or interface a using 80.0.0.0/8 and interface b using 80.0.0.0/10?

My second question is router R2's interface c has ip address 80.0.0.0/10?or any of the IP address of the block 80.0.0.0/10 for example 80.0.0.1/10?

Scenario:2

Suppose a host A, host B, router connected to 3 different ports of switch.Suppose host A has interface M and Mac address aaaa connected to switch port of N. enter image description here

My question is switch port interface N and host interface M could share same Mac address or switch has 3 different Mac address for it's interface N, P, Q?

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  • Router R1 using IP address 80.0.0.0/8 isn't possible since that address has all host bits set to zero. It's the network prefix and unusable as an actual interface address. Router R2 has 4 subnets 80.0.0.0/10, 80.64.0.0/10, 80.128.0.0/10, 80.192.0.0/10 is also not possible as these subnets all overlap with 80.0.0.0/8.
    – Zac67
    Feb 16 at 13:25
  • @Zac67 If A wants to send frame to B. My question is layer2 frame from A to switch reached by port number Or Mac address? A using destination Mac of B, but A reached to switch by using port number?
    – Alok Maity
    Feb 16 at 18:53
  • The switch receives A's frame (on port N, learns/updates A's MAC association), looks up B's MAC in its SAT/CAM, sees the association with port Q and forwards the frame out of that port.
    – Zac67
    Feb 16 at 18:58
  • @Zac67 SAT/CAM full form?
    – Alok Maity
    Feb 16 at 19:02
  • 1
    @Zac67 “Transparent” means that when you connect a switch to an Ethernet system, no changes are made in the Ethernet frames that are bridged
    – Alok Maity
    Feb 16 at 22:37

1 Answer 1

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My first question is router R1 with interface a and router R2 interface b has same ip address 80.0.0.0/8 or interface a using 80.0.0.0/8 and interface b using 80.0.0.0/10?

80.0.0.0 is a unique address, regardless of the subnet mask. So two devices cannot have that same address. Remember though that 80.0.0.0 is not a valid host address with a mask of /8 (or /10). You could use 80.0.0.1

Interfaces a and b can be on any unique subnet. They don't have to be part of the 80.0.0.0/8 subnet.

The routing table of R1 should have a route to 80.0.0.0/8, with the next hop of interface b on R2.

My second question is router R2's interface c has ip address 80.0.0.0/10?or any of the IP address of the block 80.0.0.0/10 for example 80.0.0.1/10?

Since 80.0.0.0/10 is not a valid host address, the next available address in that subnet is 80.0.0.1

My question is switch port interface N and host interface M could share same Mac address or switch has 3 different Mac address for it's interface N, P, Q?

The switch's interfaces don't have MAC addresses. Another (old) name for a switch is a transparent bridge. It transparently forwards frames based on its MAC forwarding table. If the switch has some control or management function, such as spanning tree or a management interface, those functons will have MAC addresses

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  • You should add that MAC addresses need to be unique within each network (=L2 segment). UAA MAC addresses are even meant to be globally unique but that isn't always the case today.
    – Zac67
    Feb 16 at 13:41
  • @Zac67 You just did :)
    – Ron Trunk
    Feb 16 at 15:04
  • @RonTrunk if interface a and interface always has unique ip address?
    – Alok Maity
    Feb 16 at 15:30
  • All interfaces must have unique addresses. Every house has a unique street address. Every cell phone has a unique telephone number.
    – Ron Trunk
    Feb 16 at 15:32
  • 2
    Routers do not have IP addresses. Their interfaces have IP addresses. If a router has two interfaces, each interface has a unique address (on different subnets)
    – Ron Trunk
    Feb 16 at 15:43

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