Summarization - forwarding of broadcast addresses, pg 148-149

[Tony]

On page 148 in the text when discussing a summary address of 192.168.144.0/20, it states "A router that has a summary address in the routing table will forward any packet with destination IP addresses of 192.168.144.1 through 192.168.159.254."

But on page 149 under Summarization example 1 when using the exact same summary address, 192.168.144.0/20, it states "The IP addresses that will be forwarded are 192.168.144.1 through 192.168.159.255. (Yes, the broadcast address is forwarded.)"

Why the difference or am I missing something?

Is the broadcast address forwarded by a router when it falls within a summary address?

[aguilera]

Tony, there should be no difference.

192.168.144/20 summarizes addresses 192.168.144.0 - 192.168.159.255

A packet destined to 192.168.144.255 will be forwarded using this summary address.

192.168.144.255 is an example of a directed broadcast. Routers will forward directed broadcast.

Routers will not foward broadcast 255.255.255.255 destin to everyone everywhere.

Ciao,

D. Aguilera

[Tony]

Thanks,

Tony

[stringchopper]

Tony, there should be no difference.

192.168.144/20 summarizes addresses 192.168.144.0 - 192.168.159.255

A packet destined to 192.168.144.255 will be forwarded using this summary address.

192.168.144.255 is an example of a directed broadcast. Routers will forward directed broadcast.

Routers will not foward broadcast 255.255.255.255 destin to everyone everywhere.

Ciao,

D. Aguilera


I know this is an older thread, hopefully it will "bump".

When I set up a packet tracer (virtual) lab, and ping from a device at IP 192.168.1.19 (on 192.168.1.16 /29) to the broadcast address 192.168.1.7 (for the 192.168.1.0 /29 network), the icmp reply comes back to device at 192.168.1.19 from the router that is connected to 192.168.1.0 /29.

But that same router, 192.168.1.1, does not forward the packet to the other devices that are connected to it on the network 192.168.1.0 /29

ie, .2, .3., .4, .5, .6 do not receive the icmp packet sent to 192.168.1.7 /29 ... only the router at .1 receives it.

Is that correct, or maybe I did something wrong?

[lammle]

Do you have all those hosts configured?
Also, that is probably packet tracer. Who knows what they have configured to work or not.
Todd

[stringchopper]

hosts were configured properly, but the router (192.168.1.1) that received the forwarded broadcast packet destined for 192.168.1.7, seemed to think that the IP address in the packet matched an IP address assigned to one of it's interfaces, according to the explanation given in the program when simulating and opening up the frames/packets.

I assume it's a program bug.

The first router (.16/29) did forward the broadcast to the other subnet, though.