| path | title |
|---|---|
/learnings/ops_networking |
Learnings: Ops: Networking |
If network utilizes large L3 IP space the number of neighboring nodes may flood the space of the ARP cache
Knowing that ipv4 addresses are 32 bit integers, thus made up of 4 1 byte chunks like so:
196.168.42.138
C0.A8.2A.8A
OR, in base 2
1100 0100 . 1010 1000 . 0010 1010 . 1000 1010
CIDR annotation allows you to say "I want IPs that match these same prefix of bits, and a wildcard of anything below that limit".
Given that information, a sample CIDR block makes more sense now:
196.168.42.0/23
This means, my prefix of bytes is:
11 00 01 00 . 10 10 10 00 . 00 10 10 10 . 10 00 10 10
I have a 23 bit prefix: that is, I care only about addresses matching the first 23 bytes: only these pass my filter, and the bytes to the left of that marker I do not.
Our sample here:
11 00 01 00 . 10 10 10 00 . 00 10 10 10 . 10 00 10 10
I put a !! on bit 23 here
base 10 196 . 168 . 42 . 138
base 16 C0 . A8 . 2A . 8A
base 2 1100 0100 . 1010 1000 . 0010 10!!10 . 1000 1010
Thus any address of 198.168.40.* , (198.168.0010 !! 1000) , 198.168.41.* ((198.168.0010 !! 1001), 198.168.42.* ((198.168.0010 !! 1010), 198.168.43.* ((198.168.0010 !! 1011), 198.168.44.* ((198.168.0010 !! 1100) ... etc to 198.168.47.* is matched by this CIDR block