LFS201 Knowledge Check Question 34.3
Question: 192.168.128.255 is a valid IP address for a host on a local network if the mask is configured to 255.255.255.0. True or False?
The answer is given as false, but no further explanation is provided. After googling for more info, I found out that routers use a form of classless IPv4 addressing called CIDR, with the same dotted-decimal notation but followed by forward slash and bit mask. My conclusion is the host IP address in the question above does not conform to the correct format of 192.168.128.255/24 given the bit mask of 255.255.255.0
Please kindly correct me if I am wrong. Thank you
Reference:
Cisco Press - https://www.ciscopress.com/articles/article.asp?p=330807
OpenLearn - https://www.open.edu/openlearn/science-maths-technology/computing-ict/protocols-multi-service-networks/content-section-3.5.1
Answers
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I just found out that the IPv4 address range from 192.168.0.0 to 192.168.255.255 are reserved for private or internal network addresses. Therefore 192.168.128.255 is a private address and not a public address, so obviously the answer should be false
Reading:
Opensource.com - https://opensource.com/article/16/12/cidr-network-notation-configuration-linux
IBM - https://www.ibm.com/docs/en/networkmanager/4.2.0?topic=translation-private-address-ranges0 -
Hi @nghuipen72 ,
I just found out that the IPv4 address range from 192.168.0.0 to 192.168.255.255 are reserved for >private or internal network addresses. Therefore 192.168.128.255 is a private address and not a public >address, so obviously the answer should be false
Yep, that's right. Also you can take a look to RFC1918, which refers to "Address Allocation for Private Internets":
https://datatracker.ietf.org/doc/html/rfc1918
Regards,
Luis.0 -
@luisviveropena said:
Hi @nghuipen72 ,I just found out that the IPv4 address range from 192.168.0.0 to 192.168.255.255 are reserved for >private or internal network addresses. Therefore 192.168.128.255 is a private address and not a public >address, so obviously the answer should be false
Yep, that's right. Also you can take a look to RFC1918, which refers to "Address Allocation for Private Internets":
https://datatracker.ietf.org/doc/html/rfc1918
Regards,
Luis.well the question is if it was a correct address on the local network. And local network should imply private ip addressing.
It is not a correct host address because it is broadcast ip address.
When subneting first (network) and the last (broadcast) addresses can't be used for hosts.
- For example you can see broadcast as bdr field in ip a output:
- wlp0s20f3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group
...
inet 192.168.0.11/24 brd 192.168.0.255 scope global dynamic noprefixroute wlp0s20f3
Some more details on subneting
https://en.wikipedia.org/wiki/SubnetworkAnd an interactive subnet calculator with binary AND to have how different netmasks work
http://jodies.de/ipcalc0 -
Hi @ddespa, yep, we are not supposed to assign the broadcast IP to a host (technically you can do it, but it can/will generate issues on the network). In the same way, we don't use the network address for a host.
Regards,
Luis.0
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