Answer :
To determine which OSPF network command would advertise only the 10.1.1.0 network to neighbors, we need to understand the format and purpose of the command options provided.
The command format is:
```
router(config-router)# network [network-address] [wildcard-mask] area [area-id]
```
- network-address: This is the network you wish to advertise.
- wildcard-mask: This mask is used to specify the range of addresses being matched. A wildcard mask is the inverse of a subnet mask.
- area: This specifies the OSPF area to which the network belongs.
Let's break down each option given:
1. router(config-router)# network 10.1.1.0 0.0.0.0 area O
- Wildcard mask `0.0.0.0` matches exactly the IP address specified (10.1.1.0), which doesn't cover the entire network. Therefore, it is incorrect as it won't advertise all possible hosts in the network 10.1.1.0/16.
2. router(config-router)# network 10.1.0.0 0.0.15.255 area O
- This matches a very large range of networks, not only 10.1.1.0, but also 10.1.0.0 and 10.1.2.0, so this is incorrect since it exceeds the scope.
3. router(config-router)# network 10.1.1.0 0.0.0.255 area O
- Wildcard mask `0.0.0.255` will correctly match all addresses in the 10.1.1.0/24 network. This is the right command to advertise exactly the 10.1.1.0 network.
4. None of the options listed is correct
- Since we identified option 3 as correct, this choice is not applicable.
5. router(config-router)# network 10.1.1.0 0.0.255.255 area O
- This wildcard mask `0.0.255.255` will include any network from 10.1.0.0 to 10.1.255.255, which means it advertises more networks than just 10.1.1.0.
Therefore, the correct OSPF network command to advertise only the 10.1.1.0 network is:
- Option 3: `router(config-router)# network 10.1.1.0 0.0.0.255 area O`
The command format is:
```
router(config-router)# network [network-address] [wildcard-mask] area [area-id]
```
- network-address: This is the network you wish to advertise.
- wildcard-mask: This mask is used to specify the range of addresses being matched. A wildcard mask is the inverse of a subnet mask.
- area: This specifies the OSPF area to which the network belongs.
Let's break down each option given:
1. router(config-router)# network 10.1.1.0 0.0.0.0 area O
- Wildcard mask `0.0.0.0` matches exactly the IP address specified (10.1.1.0), which doesn't cover the entire network. Therefore, it is incorrect as it won't advertise all possible hosts in the network 10.1.1.0/16.
2. router(config-router)# network 10.1.0.0 0.0.15.255 area O
- This matches a very large range of networks, not only 10.1.1.0, but also 10.1.0.0 and 10.1.2.0, so this is incorrect since it exceeds the scope.
3. router(config-router)# network 10.1.1.0 0.0.0.255 area O
- Wildcard mask `0.0.0.255` will correctly match all addresses in the 10.1.1.0/24 network. This is the right command to advertise exactly the 10.1.1.0 network.
4. None of the options listed is correct
- Since we identified option 3 as correct, this choice is not applicable.
5. router(config-router)# network 10.1.1.0 0.0.255.255 area O
- This wildcard mask `0.0.255.255` will include any network from 10.1.0.0 to 10.1.255.255, which means it advertises more networks than just 10.1.1.0.
Therefore, the correct OSPF network command to advertise only the 10.1.1.0 network is:
- Option 3: `router(config-router)# network 10.1.1.0 0.0.0.255 area O`
