In CIDR, there is no such concept as "number of subnets created" right ? As CIDR subnetting seems to be based on allocating a range of IP addresses instead.
Hmm because I came across an article about CIDR which used the example 192.168.12.0/23.
In this case, the subnet mask is 255.255.254.0 .
How do I calculate the number of subnets created in this case ?
Hmm because I came across an article about CIDR which used the example 192.168.12.0/23.
In this case, the subnet mask is 255.255.254.0 .
How do I calculate the number of subnets created in this case ?
In CIDR, there is no such concept as "number of subnets created" right ? As CIDR subnetting seems to be based on allocating a range of IP addresses instead.
When you create a subnet, you create a subnet (as in ONE subnet).
The Internet uses CIDR routing (that's classless). Subnets are arbitrary size.
Certainly, you can further subnet your /23 network, but then it's not a /23 network anymore, it's TWO /24 networks, or 4 /25 networks or 8 /26 networks.
But it ceases to be a /23 when you do that. Of course, a routing table might still refer to this collection of 16 /26 networks as a /23 netblock, but that's a different definition if you ask me.
Except that it's not a different definition. It's still a /23 network, regardless of whether or not it's further subnetted somewhere else in the network.
A subnet is not an abstract concept. It is a literal, definable thing. An aggregate network or a summarized network is still a subnet, as are the smaller subnets that make up the aggregated subnet. Both still exist and both are still called subnets.
A broadcast domain is not necessarily defined by the IP subnet(s) that the devices in the broadcast domain use. Those are arbitrary. A broadcast domain is simply a definition of L3 boundaries. Multiple L3 networks can (but shouldn't) exist within a single broadcast domain.
Broadcast domains are a L2 concept, not a L3 concept. As such, they have no bearing on the discussion of L3 addressing.
The concept of a broadcast domain determines which machines are available via a local link. Nothing more. L3 addressing is more or less irrelevant in this instance, which is why static ARP entries have a place in troubleshooting, and even work at all.
The fact that the "broadcast address" of a subnet is the last address in its range is also irrelevant.
Broadcast domain is a L2 concept, just like collision domain is a L1 concept. Discussing it in the context of subnetting is simply confusing people.
That's not accurate.
When a machine attempts to issue a Layer 3 broadcast (which is different from a layer 2 broadcast), it uses the last IP in its subnet/netmask definition.
For example, a machine at 192.168.1.1/26 (netmask 255.255.252.0) would broadcast to 192.168.1.64, and all hosts in the range 192.168.1.1-192.168.1.63 would be in the layer 3 "broadcast domain".
A machine at 192.168.1.1/24 (netmask 255.255.255.0) would broadcast to 192.168.1.255 and all hosts in the range 192.168.1.1-192.168.1.254 would be in its Layer 3 broadcast domain.
Layer 2 is a separate thing and (in Ethernet) involves MAC broadcasts to FF:FF:FF:FF:FF:FF, the boundary of which is simply defined by the physical structure of the network (the edges defined by device placement).
I suspect you know this, but I'm not sure why you are strenuously disagreeing with it, so I'm putting it out there anyway.
So much incorrect information. Explain to me why you must use a layer 3 device to separate broadcast domains? You have to use a layer 3 switch or a router. You can seperate broadcast domains on a layer 2 switch with vlans, but any broadcast in that vlan will go to all layer 2 devices configured with that vlan.
Collision domains are separated at layer 2. A switch creates a desperate collision domain between every one of its ports and whatever is connected. With a hub everything that is connected is in the same collision domain which is why Ethernet had to use CSMA/CD to stop collisions before switches.
Layer 1 is just the currents transmitted across the medium that stand for 1's and 0's.
I'm still a lowly net academy student so I could easily have some things wrong, but I know for sure that you aren't right...
Yeah I am not quite following the whole broadcast thing here. Packets sent to a broadcast IP address typically get a destination MAC addres (from ARP) of FF:FF:FF:FF:FF:FF so that the packets are flooded properly at the layer 2 (on Ethernet.) There are special cases required to properly handle IP broadcast when the layer 3 domain extends over more than one Layer 2 domain (think VPN tunnels etc) so that the IP broadcasts actually reach the remote side. IP broadcasts being the last address is certainly not irrelevant and layer 3 has these provisions on purpose. The broadcasts are handle differently on other layer 2 techs and maybe filtered or controlled in those techs. Then we also need to look at multicast which is similar in that it could be broadcasting in to hundreds of other layer 2 domains if needed.
.....
You pretty much have everything wrong.
Consider how ARP works. Machine needs to send a packet to an address. If that address is in the current subnet (link local) it sends an ARP request to the broadcast address (MAC FF:FF:FF:FF:FF:FF) asking about the IP address it needs to send to. If that address is on a different subnet (as determined by the subnet mask, which is directly related to the CIDR notation,) then the ARP request is instead for the next hop to the address (in most cases, this is a configured default gateway, but it doesn't have to be.)
ARP is meant to learn the L2 address of a host that is known only by L3 address. This can only (with the exception of proxy ARP) happen within a broadcast domain, hence why broadcast domains are a L2 concept and not a L3 concept. L3 addressing does not determine which hosts will respond to a broadcast message because broadcasts are a L2 concept.
A routing domain or autonomous system, which is much more abstract, could be considered the analog in L3 terms.
As to a collision domain, you are also wrong. Collision avoidance occurs at L1, not at L2. A hub is a L1 device. All devices connected to a hub share a common collision domain, because they are all connected to the same "cable." When you introduce a switch (which is a L2 device,) you segregate collision domains. Again, though, the L2 addressing is irrelevant because all you've established is a method for full duplex communication whereby both devices on the link can send at the same time...which is the same thing as collision avoidance.
This correlates to a broadcast domain, and to your question about why you need a L3 device, as follows: a switch (or in the old word, a bridge) segregates collision domains on a per port (logical or otherwise) basis the same way a router segregates broadcast domains on a per port (logical or otherwise) basis. On a switch, every port is its own collision domain, and the switch uses the L2 address to switch frames between the collision domains. On a router, every port is its own broadcast domain, and the router uses L3 addresses to route packets between the broadcast domains.
But here's the important thing: inside a collision domain, the L2 address is not relevant to avoiding collisions and being able to transmit data...just as inside a broadcast domain, the L3 address is not relevant to sending ethernet frames between hosts.
The OSI Physical layer provides the means to transport across the network media the bits that make up a Data Link layer frame. This layer accepts a complete frame from the Data Link layer and encodes it as a series of signals that are transmitted onto the local media. The encoded bits that comprise a frame are received by either an end device or an intermediate device.
The delivery of frames across the local media requires the following Physical layer elements:
The physical media and associated connectors
A representation of bits on the media
Encoding of data and control information
Transmitter and receiver circuitry on the network devices
At this stage of the communication process, the user data has been segmented by the Transport layer, placed into packets by the Network layer, and further encapsulated as frames by the Data Link layer. The purpose of the Physical layer is to create the electrical, optical, or microwave signal that represents the bits in each frame. These signals are then sent on the media one at a time.
It is also the job of the Physical layer to retrieve these individual signals from the media, restore them to their bit representations, and pass the bits up to the Data Link layer as a complete frame.
ARP packets are always sent to the broadcast mac address.doesn't this mean that the destination MaC is the routers