path: root/include/numgen.h
diff options
authorPablo Neira Ayuso <>2016-08-26 14:41:41 +0200
committerPablo Neira Ayuso <>2016-08-29 20:30:28 +0200
commit13eeed6ea6f0a5d1353ee5ad14c4322695b4f59b (patch)
treedee935f0f40bb41399b8d5d0c8ab4f23e53fd7d3 /include/numgen.h
parent1ed9a3726c01fda218f37b7f4555c8b7106521ef (diff)
src: add numgen expression
This new expression allows us to generate incremental and random numbers bound to a specified modulus value. The following rule sets the conntrack mark of 0 to the first packet seen, then 1 to second packet, then 0 again to the third packet and so on: # nft add rule x y ct mark set numgen inc mod 2 A more useful example is a simple load balancing scenario, where you can also use maps to set the destination NAT address based on this new numgen expression: # nft add rule nat prerouting \ dnat to numgen inc mod 2 map { 0 :, 1 : } So this is distributing new connections in a round-robin fashion between and Don't forget the special NAT chain semantics: Only the first packet evaluates the rule, follow up packets rely on conntrack to apply the NAT information. You can also emulate flow distribution with different backend weights using intervals: # nft add rule nat prerouting \ dnat to numgen inc mod 10 map { 0-5 :, 6-9 : } So gets 60% of the workload, while gets 40%. We can also be mixed with dynamic sets, thus weight can be updated in runtime. Signed-off-by: Pablo Neira Ayuso <>
Diffstat (limited to 'include/numgen.h')
1 files changed, 7 insertions, 0 deletions
diff --git a/include/numgen.h b/include/numgen.h
new file mode 100644
index 00000000..bec18e5a
--- /dev/null
+++ b/include/numgen.h
@@ -0,0 +1,7 @@
+extern struct expr *numgen_expr_alloc(const struct location *loc,
+ enum nft_ng_types type, uint32_t until);
+#endif /* NFTABLES_NUMGEN_H */