On Sun, 30 Jul 2023 15:30:14 -0500 (CDT)
Tim Mooney <Tim.Mooney@xxxxxxxx> wrote:
>
> All-
>
> I haven't been able to find anywhere in the nftables wiki that talks
> about "Dos and Don'ts" from an efficiency perspective, especially for
> people that may be coming from iptables/ip6tables to nftables. If it's
> there and I've missed it, please point me at it.
>
> I have a mix of 32 iptables and ip6tables rules on a RHEL 7 box that I
> want to convert to nftables for RHEL 9 (kernel 5.14.0 + Red Hat vendor
> sauce, nftables 1.0.4).
>
> The obvious thing to do would be to just directly translate each rule to
> nftables, and have 32 nftables rules.
>
> However, the iptables rules are all pairs of
>
> -A ports_allow -p tcp -m tcp -s X.Y.0.0/16 --dport 80 -j ACCEPT
> -A ports_allow -p tcp -m tcp -s X.Y.0.0/16 --dport 443 -j ACCEPT
>
> -A ports_allow -p tcp -m tcp -s A.B.C.D/32 --dport 80 -j ACCEPT
> -A ports_allow -p tcp -m tcp -s A.B.C.D/32 --dport 443 -j ACCEPT
>
> So I could cut the number of ntables rules in half just by using
>
> dport { 80, 443 }
>
> in the translated rule.
>
> The question is, *is it more efficient*, from a packet processing
> perspective, to do that? My guess is that it is, but can anyone with
> expertise confirm? If it is more efficient, what type of efficiency
> improvement are we talking about, roughly?
# nft -d netlink -c -f - <<<'table ip t { chain c { ip saddr 10.0.0.0/16 tcp dport { 80, 443 } accept; }; }'
ip (null) (null) use 0
__set%d t 3 size 2
__set%d t 0
element 00005000 : 0 [end] element 0000bb01 : 0 [end]
ip t c
[ payload load 2b @ network header + 12 => reg 1 ]
[ cmp eq reg 1 0x0000000a ]
[ meta load l4proto => reg 1 ]
[ cmp eq reg 1 0x00000006 ]
[ payload load 2b @ transport header + 2 => reg 1 ]
[ lookup reg 1 set __set%d ]
[ immediate reg 0 accept ]
Unsurprisingly, repeating the rule can be shown to demonstrate twice the number of instructions. You may find it difficult to measure the difference, however.
>
> Similarly, all of the rules list CIDR ranges or individual IPs, though
> there are a mix of IPv4 and IPv6 ranges. I therefore could greatly reduce
> the number of rules by creating a couple of named sets, one for IPv4 and
> one for IPv6, and match the 'ip saddr' against the sets.
You are definitely on the right track. Maps and/or verdict maps incorporating concatenations of the form "ipv4_addr . inet_service" and "ipv6_addr . inet_service" might also prove useful, depending on your exact requirements.
--
Kerin Millar
