What is difference in ip scheme of /32 and /24 in router settings

dankyle67
dankyle67 used Ask the Experts™
on
Hi,
was recently trying to set up a new ip mapping on a netscreen 5gt and noticed that in the ip address box you could either use /24 or /32 after the entry for instance of the static ip supplied by the isp.  Didnt want to put incorrect entry so would appreciated an explanation of when to use which number either /24 or /32.  thanks
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Don JohnstonInstructor
Top Expert 2015

Commented:
If you mean the untrust interface, you would use whatever IP address/mask that your ISP has assigned you to use.
JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018

Commented:
you could either use /24 or /32 after the entry for instance of the static ip supplied by the isp



/32 is a subnet mask of 255.255.255.255 and so is one IP address which is all you want for the external IP field in a Juniper 5GT (at least we just use one external IP address in our several client 5GT setups.

Author

Commented:
We have 4 static ip addresses which we have to map to 3 internal servers.  The other static ip we would use for the netscreen itself.  So if i put /29 is that better since we have the 4 addresses or will /32 still work as long as i create the 3 separate ip mappings?  What about /24 is that for the internal client ips?  We only have 22 machines at the office.
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JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018

Commented:
You would have to check your 5GT to see if it can map 3 separate external IP addresses internally. I use internal addresses for multiple servers in my environment.
Business Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018
Commented:
I use /24 to set up the internal range multiple devices (servers or workstations)
Qlemo"Batchelor", Developer and EE Topic Advisor
Top Expert 2015
Commented:
The netmask needs to be as provided by the ISP, as said already. Otherwise you might not be able to reach some other sites, or not allow routing to your additional public IPs.
So, if you have 4 usuable addresses your IP block spans 8 addressses, corresponding to /29. The first and last one are reserved, one is used by the provider as the next hop for your router.
JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018

Commented:
@dankyle67  - Thank you and I was happy to help.

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