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I am used to seeing ip addresses of the form 10.244.0.1/24. What does an address cidr notation /32 mean ?

$ ip a
...snipped...
4 : flannel.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1410 qdisc noqueue state UNKNOWN group default                                                           
[4/401]
    link/ether 06:fb:8c:da:42:0b brd ff:ff:ff:ff:ff:ff
    inet 10.244.0.0/32 scope global flannel.1
       valid_lft forever preferred_lft forever
    inet6 fe80::4fb:8cff:feda:420b/64 scope link 
       valid_lft forever preferred_lft forever
  • It means the subnet mask is 255.255.255.255 (or that it is the only IP in it's network) – Jesse_b Feb 5 '18 at 3:59
  • It is new to me that an address ending in .0 is a valid IP. I am familiar with class C addresses in which if the last octet is 0, it is used to refer to the network. I'm such an ignoramus. – Bon Ami Feb 5 '18 at 4:07
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    .0 being a valid IP is new to me as well, don't feel bad :p – Jesse_b Feb 5 '18 at 4:12
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    A .0 address isn't always the network address, and the network address doesn't always end in .0 (it's always the first address in the subnet). e.g. in a /23 network, the subnet spans from x.x.x.0 to x.x.x+1.255 - there is a valid .0 address in the middle of that. BTW, address classes have been obsolete for well over 20 years now - obsoleted by Classless Inter-Domain Routing (CIDR), the standard "address/prefix" used everywhere now. – cas Feb 5 '18 at 5:24
  • In the RFC4632 table at the end of section 3.1 a /32 address is called a host route and is defined with a value of n.n.n.n meaning (IMhO) that it can have any value. This is also related. – Isaac Feb 5 '18 at 5:25
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It means all the subnet mask bits are "ON" and the subnet mask for that IP address is 255.255.255.255.

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