Stupid Question maybe?

Wed Dec 19 16:24:33 UTC 2018

>Why do you think the network portion needs to be contiguous?

Just because some equipment at one time let you configure a non-contiguous mask does not make it correct configuration.  Please come up with any valid use case for a non-contiguous network (note NETWORK, not any other purpose) mask.

>Well, it does now. But that was not always the case.

It has ALWAYS been the only correct way to configure equipment and is a requirement under CIDR.  Here were your commonly used netmasks before CIDR/VLSM :

255.0.0.0
255.255.0.0
255.255.255.0

Which one is not contiguous?

>https://www.quora.com/Why-is-the-subnet-mask-255-255-255-64-invalid/answer/Patrick-W-Gilmore

In this example, the writer used it as a parlor trick to actually break a network.  That's why you don't do it and it was never a good configuration.  It just exploited a UI that did not validate the netmask.

>https://www.quora.com/Why-is-the-subnet-mask-255-255-255-64-invalid

In the second cited link, they are talking about using a non-contiguous mask in an access control function.  That is perfectly valid to do, it just is not a NETmask anymore.  By definition a netmask identifies the network portion of an address.  In the cited example they are defining a group of subnets to an ACL.

Steven Naslund
Chicago IL

>
>--
>TTFN,
>patrick
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.nanog.org/pipermail/nanog/attachments/20181219/22701447/attachment.html>