Michael Simpson wrote:
On 12/2/08, Adam Greene <[EMAIL PROTECTED]> wrote:
How does one get around the side-effect of not allowing broadcasts; i.e.
wouldn't this break ARP functionality?
Not within the subnet
using ethernet arp is only on the local segment and won't traverse the router
no ip directed broadcast stops broadcasts from a different subnet
snipped from
<http://www.cisco.com/en/US/docs/ios/12_3/ipaddr/command/reference/ip1_i1g.html#wp1081245>
An IP directed broadcast is an IP packet whose destination address is
a valid broadcast address for some IP subnet, but which originates
from a node that is not itself part of that destination subnet.
A router that is not directly connected to its destination subnet
forwards an IP directed broadcast in the same way it would forward
unicast IP packets destined to a host on that subnet. When a directed
broadcast packet reaches a router that is directly connected to its
destination subnet, that packet is "exploded" as a broadcast on the
destination subnet. The destination address in the IP header of the
packet is rewritten to the configured IP broadcast address for the
subnet, and the packet is sent as a link-layer broadcast.
mike
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Or to put it another way...
Arp uses a destination IP of 255.255.255.255, which is the 'limited
broadcasts address'. Packets with this destination are never routed
between subnets.
Directed broadcast destination IPs begin with a subnet's network prefix,
so for an interface with IP 192.168.10.1/24 the directed broadcast
address of its attached subnet is 192.168.10.255. These can be routed
between subnets.
Paul.
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