From mboxrd@z Thu Jan 1 00:00:00 1970 From: Simon Kirby Subject: Re: Inability to IPVS DR with nft dnat since 9971a514ed26 Date: Wed, 27 Mar 2019 08:34:23 -0700 Message-ID: <20190327153422.GA1161@hostway.ca> References: <20190327062650.GA10700@hostway.ca> <20190327093027.gmflo27icuhr326p@breakpoint.cc> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20190327093027.gmflo27icuhr326p@breakpoint.cc> Sender: netdev-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Florian Westphal Cc: netdev@vger.kernel.org, netfilter-devel@vger.kernel.org, lvs-devel@vger.kernel.org On Wed, Mar 27, 2019 at 10:30:27AM +0100, Florian Westphal wrote: > > I bisected this to 9971a514ed2697e542f3984a6162eac54bb1da98 ("netfilter: > > nf_nat: add nat type hooks to nat core"). > > > > It should be pretty easy to see this with a minimal setup: > > > > /etc/nftables.conf: > > > > table ip nat { > > chain prerouting { > > type nat hook prerouting priority 0; > > > > ip daddr $ext_ip dnat to $vip > > } > > chain postrouting { > > type nat hook postrouting priority 100; > > > > # In theory this hook no longer needed since this commit, > > # but we also need to do some unrelated snatting. > > } > > } > > > > /etc/sysctl.conf: > > > > net.ipv4.conf.all.accept_local = 1 > > net.ipv4.vs.conntrack = 1 > > > > IPVS DR setup: > > > > ipvsadm -A -t $vip:80 -s wrr > > ipvsadm -a -t $vip:80 -r $real_ip:80 -g -w 100 > > I have a hard time figuring out how to expand $ext_ip, $vip and $real_ip, > and where to place those addresses on the nft machine. $ext_ip is something reachable from the "outside"; it just has to be something which can get to the nft box that isn't the real server or the same host. We have a public IP in this case. $vip is something that is on the local LAN "behind" the nft box. In our case this is an rfc1918 IP address. $real_ip is on the same subnet as the $vip and is just a way for IPVS to resolve the neighbor of one of the real servers in order to forward the packet. With this example configuration, IPVS is basically equivalent to: ip route add $vip via $real_ip Except that it hooks the input path because $vip is expected to be bound locally...and normally you have multiple real servers and some algorithm selected for balancing. So, I guess I didn't mention that, and you also need to bind $vip to the nft box, and also to the real server if you want it to actually be able to respond. "LVS-HOWTO" has info on how to set up LVS-DR. The only difference here is that we're using it in a relatively new (2009) configuration where "DR" (Direct Return) mode is actually symmetric and replying back to the nft box (symmetric) instead of directly to a separate router. This lets NAT actually work since it can see traffic in both directions. Simon-