Math operations

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nftables includes some interesting math operations generators which can be used to perform advanced operations like Load balancing.

Number generator

The number generator statement has these options:

  • type: inc/random.
  • modulus: maximun number
  • offset: from what value you want to start from

Some examples, distributing marks to packets:

table ip t {
	chain c {
		mark set numgen inc mod 4 offset 3
		mark set numgen random mod 50 offset 20
		mark set numgen inc mod 100
	}
}

The statement numgen inc mod 2 offset 100 will generate numbers in a series like 100, 101, 100, 101...

Hashing

nftables support hashing of any arbitrary key combination:

table ip t {
	chain c {
		mark set jhash ip saddr mod 2
		mark set jhash ip saddr . tcp dport mod 2
		mark set jhash ip saddr . tcp dport . iiftype mod 2
	}
}