ICMP echo request over broadcast subnet

I'm looking at a boson practice test .there's a question that mentions an r1-r4 serial link with a subnet 192.168.7.128.I'm wondering why the question reckons that the icmp request is going over a BROADCAST subnet when it goes over this link? All the other subnets in the question are ZERO subnets, namely 172.30.0.0, 10.0.0.0 and 192.168.5.0 .Why are these last 3 subnets ZERO subnets and why is the first one a BROADCAST one?

Any help would be gratefully received.
thanks,
Andrew

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tim100

Andrew Newman wrote: »

I'm looking at a boson practice test .there's a question that mentions an r1-r4 serial link with a subnet 192.168.7.128.I'm wondering why the question reckons that the icmp request is going over a BROADCAST subnet when it goes over this link? All the other subnets in the question are ZERO subnets, namely 172.30.0.0, 10.0.0.0 and 192.168.5.0 .Why are these last 3 subnets ZERO subnets and why is the first one a BROADCAST one?
Any help would be gratefully received.
thanks,
Andrew

192.168.7.128 is the subnet address. What is the practice test question?

Andrew Newman

Hi, I can give you the question and possible answers, but I can't really copy the network diagram.anyway, here goes;
The figure shows an internetwork with ip addresses and default gateways for some devices.RIP-2 has been configured correctly on all the routers and the ip subnet zero command configured on all the routers.A design goal for this network is for all devices to be able to ping devices on other LANs.Keeping that goal in mind, which of the following statements are true about the internetwork.
a)When PC4 pings PC3, the ICMP echo request passes over 2 zero subnets.
b)When PC3 pings PC4, the ICMP e3cho request flows over abroadcast subnet.
c)When PC3 pings PC1, the ICMP echo request is discarded because a zero subnet is used in the route.
d)When PC1 pings PC2, the ICMP echo request is discarded because a zero subnet is used in the route.

Andrew Newman

actually, am I right in saying that a broadcast subnet is one where all the bits in the subnet part can be 1s? And that, a zero subnet is a subnet where not all of the bits in the subnet part can be 1s?

tim100

Andrew Newman wrote: »

actually, am I right in saying that a broadcast subnet is one where all the bits in the subnet part can be 1s? And that, a zero subnet is a subnet where not all of the bits in the subnet part can be 1s?

If the mask is 255.255.255.128 then subnet 192.168.7.128 would be considered a broadcast subnet also known as the all ones subnet. When "ip subnet-zero" is enabled, which is the default since IOS 12.0, it allows use of the all ones subnet as well as subnet zero.

Andrew Newman

Hi Tim, thanks for that