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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
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
18.104.22.168, this is a subnet-directed broadcast if the class B network 128.1 has a subnet
mask of 255.255.255.0, but it is not a broadcast if the subnet mask is 255.255.254.0
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 255.255.255.0, then the IP address 22.214.171.124 is an allsubnets-directed broadcast. But if the network is not subnetted, then this is a net-directed
Current feeling [Almquist 1993] is that this type of broadcast is obsolete.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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- Spring '12