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TOPIC: Proxy Arp/Subnets

Proxy Arp/Subnets 11 years 9 months ago #22514

I was reading a Proxy ARP paper from Cisco and in the example there were two computers (among others) that were configured as such:

Host A:
Host B:

The paper said "Host A believes that it is directly connected to all of network"

Does this mean that the /16 network can communicate to any 172.16.x.x network? (x.x being numbers). I always thought of network being different from /24. Is this not the case because this addresses is subnetted?

Re: Proxy Arp/Subnets 11 years 9 months ago #22515

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Host A:
Host B:

Subnet /16
having the subnet block from -, so the HostB's subnet also included on this. Hence obviously Host A can communicate with HostB. As well as from HostB's point of view the network Address will be and Bradcast will be so the traffic wont go beyond this.


Re: Proxy Arp/Subnets 11 years 9 months ago #22518

I think what confuses me is why they say the subnet determins which part of the IP address is Network/Subnet and which is host portion.

This to me would put Host A on the network and Host B on the network making them on different networks. I guess the subnet determines which IP range it is in?

Does the communication work in both directions? So, any subnet of can communicate to any other subnet of

I thought the point of subnetting was to get more networks/hosts...

Re: Proxy Arp/Subnets 11 years 9 months ago #22525

It helps to remember that the subnet mask is applied on a node, so if Host A's address is then Host A thinks it is on the network and so, as far as host A is concerned, anything with the address 172.16.x.x is on it's local network. Host B ( ) will have a different opinion because the key is to consider which host you are sitting in and looking out at the world from

Re: Proxy Arp/Subnets 11 years 9 months ago #22528

So, with that being the case, does that mean Host B is on a different network than Host A? and Host B could not communicate to Host A? But, Host A can talk to Host B?

Re: Proxy Arp/Subnets 11 years 9 months ago #22532

Host B is on a different network to Host A from Host B's point of view, but not from Host A's point of view. From Host A's point of view they are on the same network. The outcome all depends on the mask set at each node
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