The 255255255 in the subnet mask correlates to the

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host address portion of the IP address. The 255.255.255 in the subnet mask correlates to the network address of the IP address. As a general rule, you can determine the network and host addresses in an IP address by looking at the placement of the zeroes in the subnet mask. Let's take a look at an example network to see how this works. Let's say all the hosts on this network use a subnet mask of 255.0.0.0 and because this is the default subnet for class A addresses, let's say the hosts have the following IP addresses, 10.1.50.8, 10.1.6.21 and 10.1.100.22. In this network the last three octets in the subnet mask are zeroes. This means that the host addresses are the last three octets of the IP addresses and since the first octet in the subnet mask is 255, the first octet of the IP address is the network address. IP Address Configuration Considerations 2:14-4:08 There are a few considerations you need to take into account when working with IP addresses and subnet masks. The first is the fact that all hosts on the network must use the same network address to communicate. For example, if one host has an IP address of 11.1.100.22 and the other has an IP address of 10.1.6.122, even though both hosts use the same subnet mask, the hosts won't be able to communicate with each other because one has a network address of 10 while the other has a network address of 11. Now let's say that we've correctly configured the IP addresses for our hosts, but we've improperly configured the subnet mask on one host to be 255.255.0.0. As you can see, improperly configuring the subnet mask changes the network address for the host so instead of the host having 10 as its network address like the other host, it now has a network address of 10.1. Now the hosts are on two separate networks and can't communicate with each other. The second consideration is that IP addresses must be unique. No two hosts can have the same host address. And the last consideration is that every network has two reserved addresses that can't be assigned to hosts. The first reserved address is the network address, which is the first IP address on a network or the IP address that ends in a zero. For example, 192.168.1.0 or 10.0.0.0. The second is the broadcast address, which is the IP address or the address that ends in 255. For example, 192.168.1.255 or 10.0.0.255. These are the settings that must be configured in order for hosts to communicate within a single network segment. However, if hosts need to be able to communicate with external networks such as the internet, they need to be configured with a default gateway address. Default Gateway Address 4:09-5:14 Remember, the default gateway address is the IP address of the network's default gateway, also called a router. It allows hosts to communicate with external networks. Let's say that this host wants to send a file to a computer with an IP address of 72.68.54.22. Before the file is sent, the host will look at the recipient's address. When it does, it'll say, "Hey, this isn't going to any hosts on my network, so I better send this to the default gateway," and because it has a default gateway address configured, it sends it to the router up here, which then forwards it the appropriate network.
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  • Spring '14
  • Computer network, Local area network, Network topology, Metropolitan area network

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