TCP IP Illustrated

Htm 3 of 12 12092001 144700 chapter 12 broadcasting

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Unformatted text preview: then used as the destination address for datagrams sent out the interface. The Host Requirements RFC takes no stand on the issue of whether a multihomed host should send a file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/broadcas.htm (3 of 12) [12/09/2001 14.47.00] Chapter 12. Broadcasting and Multicasting limited broadcast out all its interfaces. Net-directed Broadcast The net-directed broadcast address has a host ID of all one bits. A class A net-directed broadcast address is netid.255.255.255, where netid is the class A network ID. A router must forward a net-directed broadcast, but it must also have an option to disable this forwarding. Subnet-directed Broadcast The subnet-directed broadcast address has a host ID of all one bits but a specific subnet ID. Classification of an IP address as a subnet-directed broadcast address requires knowledge of the subnet mask. For example, if a router receives a datagram destined for, this is a subnet-directed broadcast if the class B network 128.1 has a subnet mask of, but it is not a broadcast if the subnet mask is (0xfffffe00). All-subnets-directed Broadcast An all-subnets-directed broadcast address also requires knowledge of the destination network's subnet mask, to differentiate this broadcast address from a net-directed broadcast address. Both the subnet ID and the host ID are all one bits. For example, if the destination's subnet mask is, then the IP address is an allsubnets-directed broadcast. But if the network is not subnetted, then this is a net-directed broadcast. Current feeling [Almquist 1993] is that this type of broadcast is obsolete. It is better to use multicasting than an all-subnets-directed broadcast. [Almquist 1993] notes that RFC 922 requires that an all-subnets-directed broadcast be sent to all subnets, but no current routers do so. This is fortunate since a host that has been misconfigured withou...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

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