I am trying to create a firewall rule to allow Microsoft Teams thru my firewall. I can see here https://docs.microsoft.com/en-us/microsoft-365/enterprise/urls-and-ip-address-ranges?view=o365-worldwide#skype-for-business-online-and-microsoft-teams

that is the address used but the ip that is recorded in my router is

The 89.125 can change from time to time but when I looked it up on https://ipinfo.io/ its 'route' is

I would like to be able to create a fire wall rule for this but I am unsure of what means and how to construct the firewall rule

  • This is not really about firewalls or security. This is really just about IP addressing. as the answer below shows. This would have been better asked on a networking site. – schroeder Nov 26 '20 at 7:51

The is Classless Inter-domain Routing CIDR notation (RFC 4632).

The IP Calculator by Krischan Jodies illustrates this nicely:

Address:            00110100.01110000.00000000.00000000
Netmask: = 14      11111111.11111100.00000000.00000000
Wildcard:           00000000.00000011.11111111.11111111
Network:         00110100.01110000.00000000.00000000
Broadcast:        00110100.01110011.11111111.11111111
HostMin:            00110100.01110000.00000000.00000001
HostMax:        00110100.01110011.11111111.11111110
Hosts/Net: 262142

As has host range, the belongs to it.

But just allowing is not enough, as the site lists several ranges for the service. You would have to add them all in your rules to make it work reliably.

A firewall could be many things: it is impossible to tell how to construct rules for your firewall.

  • thanks..my router allows for Range Address and if covers to could I not just use that range as from start to end ip? – kurasa Nov 26 '20 at 7:08
  • 3
    You could, but CIDR notation is a more compact and easier to remember form. If you work with networks, it's worth learning. It's widely used. – vidarlo Nov 26 '20 at 7:11
  • 1
    CIDR is much more efficient when matching address prefixes. With software-based routers/firewalls it uses less CPU cycles, and with hardware-based devices it uses just a single TCAM entry. – Zac67 Nov 26 '20 at 10:43
  • 1
    @Zac67: Exactly, and sometimes a range is internally converted to CIDR notation anyway. Therefore, by specifying just the host address range instead of the whole i.e. you may actually end up adding,, ...,,, ..., & Which is 34 separate CIDR ranges instead of the one. – Esa Jokinen Nov 26 '20 at 11:14

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