Unanswered Question
Aug 19th, 2007
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Hi forum,

How do i use a single mask for the below:

site a) 172.30.x.x & 172.30.64.x - can i use 255.255.128.x for the mask? currently this site is using vlsm.

site b and site c) 172.30.128.x and 172.30.192.x each. can i use as the mask?

Thanks much,


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gng4life Sun, 08/19/2007 - 06:14
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Hello PN,

You'll have to make a few changes. For instance, in Site A, you list it as 172.30.x.x and 172.30.64.x with both having a /17 mask. That is overlapping. It would have to look something like this: and

Site B and C: and

But are sure about this? A /17 mask gives over 32,000 host IPs, do you really need that many? The /18 gives you over 16,000 IPs, that's still quite a bit.

How many hosts are you expecting on a subnet? I have worked on some very large networks and I've never used that many hosts on a single subnet.

Also, this looks like it should move to the LAN/Switching/Routing or WAN Routing/Switching forum. Thanks

Let us know...

paulnigel Sun, 08/19/2007 - 16:12
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Hi gng4life,

Thanks much for the clarification.

Actually within site A, I have mask like,, etc. I just want to summarize them together using like the 17/18 bit mask, is this possible?

Thanks much,



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