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easy broadcast question
- Thread starter siznad
- Start date
No.. broadcasts are stopped at the router .. unless arrangements have been made like dhcp helper, udp forward, tcp forward and so on..
----LAN1------Router1--------LAN2 -----Host
If the host on LAN2 sends out a broadcast, every station on LAN2 will see it.. including the router. But, the router will not forward it to LAN1 unless it's been configured to do so.
Here is a fun explanation on this.. I prefer the *expert* in black leather but the red does nicely
MikeS
Find me at
"Take advantage of the enemy's unreadiness, make your way by unexpected routes, and attack unguarded spots."
Sun Tzu
----LAN1------Router1--------LAN2 -----Host
If the host on LAN2 sends out a broadcast, every station on LAN2 will see it.. including the router. But, the router will not forward it to LAN1 unless it's been configured to do so.
Here is a fun explanation on this.. I prefer the *expert* in black leather but the red does nicely
MikeS
Find me at
"Take advantage of the enemy's unreadiness, make your way by unexpected routes, and attack unguarded spots."
Sun Tzu
- Thread starter
- #3
Yeah- he does a great job at making some dry stuff very fun to read through.. and it's pretty solid info also.
MikeS
Find me at
"Take advantage of the enemy's unreadiness, make your way by unexpected routes, and attack unguarded spots."
Sun Tzu
MikeS
Find me at
"Take advantage of the enemy's unreadiness, make your way by unexpected routes, and attack unguarded spots."
Sun Tzu
- Thread starter
- #5
A directed boadcast would be used if you were sitting on a different subnet. With a directed boadcast your router will sends the packet to to correct network ex: 192.168.1.x/24. Then every host on the subnet would look at the broadcast. The router will not send the broadcast out to any other networks except the 192.168.1.x/24 network.
- Thread starter
- #7
They dont.. which is why you use a command like IP HELPER which lets the router take the broadcast packet and repackage it to send it across a network to another router.
THis is how you can hand out DHCP across a WAN from corporate to the remote office or enable windows browsing.
Where IP HELPER forwards ten common broadcast based protocols like DHCP for example, you can do the same thing with UDP or TCP FORWARD where a single protoocol is specified to be forwarded instead of ten.
ports forward are:
67
68
69
37
49
53
137
138
(I'll let you figure out the names to the UDP port number)
A directed broadcast is useful for the DHCP server thing.. you can send the packet 192.168.1.255 which means all of the subnet 192.168.1.x will get the broadcast. A cleaner way is to specify which IP should be getting the broadcast.. so you can say 192.168.1.200 where .200 is the DHCP server. It's still a broadcast packet but it's directed to single IP address which in this case is .200
Like this:
!
ip helper-address <address>
!
The address argument specifies a destination broadcast or host address to be used when forwarding such datagrams. You can have more than one helper address per interface.
See this document:
MikeS
Find me at
"Take advantage of the enemy's unreadiness, make your way by unexpected routes, and attack unguarded spots."
Sun Tzu
THis is how you can hand out DHCP across a WAN from corporate to the remote office or enable windows browsing.
Where IP HELPER forwards ten common broadcast based protocols like DHCP for example, you can do the same thing with UDP or TCP FORWARD where a single protoocol is specified to be forwarded instead of ten.
ports forward are:
67
68
69
37
49
53
137
138
(I'll let you figure out the names to the UDP port number)
A directed broadcast is useful for the DHCP server thing.. you can send the packet 192.168.1.255 which means all of the subnet 192.168.1.x will get the broadcast. A cleaner way is to specify which IP should be getting the broadcast.. so you can say 192.168.1.200 where .200 is the DHCP server. It's still a broadcast packet but it's directed to single IP address which in this case is .200
Like this:
!
ip helper-address <address>
!
The address argument specifies a destination broadcast or host address to be used when forwarding such datagrams. You can have more than one helper address per interface.
See this document:
MikeS
Find me at
"Take advantage of the enemy's unreadiness, make your way by unexpected routes, and attack unguarded spots."
Sun Tzu
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