![]() This normally is not such an issue with stateful firewalls since the first packet to create a new session would need to be fully evaluated anyway and the rest of the traffic would immediately match the existing established session.īroadcom, MediaTek, Marvell/Cavium all have their own similar implementations (all proprietary) in their SoCs. Note that cut-through-forwarding on routers with firewalls also will bypass firewall evaluation. It is still the routing evaluation that is the most intensive, by far. This is why much of the processing is skipped since this lookup is done very early. What most routing acceleration (hardware offloading) does is to perform the full routing evaluation for the first packet in a session, save the destination MAC and exit interface (with other details), then for remaining traffic in that session skip the routing evaluation and use the saved entry in the table. This is routing and is computationally expensive. You can also run 'nvram show'.Īs a NAT accelerator for IPV4 I am surprised at how much overhead netfilter actually takes for packet processing and the successful offload of ctf.ko.CTF (and similar technologies) don't really have anything to do with NAT specificallyĪny host that needs to transmit an IP packet must determine:ģ) The interface through which that packet should be sent (exit interface) To see if you have CTF enabled you should be able to run 'lsmod' and see 'ctf' in the results. # as well as a mark rule in the mangle chain. # already used by Advanced Tomato in the mangle chain for same-RFC1918 intravlan. The below ports are marked for no accelerated CTF for NAT loopback. # Using CTF (Cut-Through Forwarding) drops the load on the router CPU almost entirely but breaks NAT loopback, usr/sbin/iptables -w -I FORWARD 1 -i br2 -o br0 -p tcp -d 192.168.1.1 -dport 993 -j ACCEPT usr/sbin/iptables -w -I FORWARD 1 -i br2 -o br0 -p tcp -d 192.168.1.1 -dport 465 -j ACCEPT usr/sbin/iptables -w -I FORWARD 1 -i br2 -o br0 -p tcp -d 192.168.1.1 -dport 443 -j ACCEPT The work-around for NAT loopback/hairpinning on interVLAN forwarding. Those using Tomato and it's variants as well as others such as DD-WRT, Merlin, etc may want to consider enabling CTF. Note the use of -j MARK in the -t mangle chain. Using this for inter-VLAN allowing an intrusted VLAN on br2 access to the trusted VLAN's specific resources on a host on that VLAN on br0. CTF kills loopback/hair-pinned NAT so for port forwarding and internal access without DNS changes to reflect RFC 1918 instead of the WAN IP you have to use -j MARK to connmark the packets to avoid CTF. Speed changes includes processing all the ACLs. Most of the CPU usage was IRQ handling I assume as packets moved towards Linux's slower netfilter handling. Dropped CPU load on the router from 80% to 0.8% during 230Mbit of bandwidth to the WAN. So yesterday I enabled Cut-Through Forwarding, evidently it's a Broadcom kernel module that offloads netfilter via association of L2/3 switching via 元/L4 params. ![]()
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