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Hello,
On Tue, 20 Oct 2020, Damien Claisse wrote:
> I'm trying to understand a limitation in ipvlan/netfilter that prevents doing
> routed IPVS with source NAT inside a namespace.
>
> Setup is the following: there is an "lvs" namespace, with an ipvlan interface
> (in l3 mode) moved to this namespace, linked to physical interface. Goal is
> to isolate load balanced traffic in a separate namespace.
> This setup is working flawlessly with l3 routed IPIP encapsulation, but I
> also have a use case for applications that don't support encapsulation, hence
> the need to do l3 routed load balancing with source NAT.
> Issue is that if I put iptables NAT rule in namespace using ipvs module,
> nothing happens, packet is forwarded but source IP is not translated. It
> seems like netfilter is blind to ipvlan l3 traffic. I also tried using "l3s"
> mode that should to go through netfilter, but in that case, packets for
> virtual IPs are rejected with a TCP reset. Virtual IPs in namespace seem not
> visible to this mode.
>
> I'm wondering what would be the best way to make it happen:
> - patch ipvlan to lookup for VIPs in namespaces
> - patch netfilter ipvs NAT module to translate in root namespace
> - any other better idea is welcome
>
> Please find below commands to reproduce the issue. In this example physical
> load balancer interface is enp4s0, virtual IP is 192.168.42.1 (to be exported
> by a routing protocol, or route manually added to a client in same subnet as
> load balancer for testing), load balancer IP is 192.168.10.10, and real
> server IP is 192.168.20.20
>
> - In root namespace:
> ip netns add lvs
> ip link add ipvlan0 link enp4s0 type ipvlan mode l3s
> ip link set ipvlan0 up
> ip link set ipvlan0 netns lvs
>
> - In lvs namespace (ip netns exec lvs bash):
> ip addr add 192.168.42.1/32 dev ipvlan0
> ip route add default via 192.168.10.10 dev ipvlan0 onlink
> ipvsadm -A -t 192.168.42.1:80 -s rr
> ipvsadm -a -t 192.168.42.1:80 -r 192.168.20.20:80 -m
> iptables -t nat -A POSTROUTING -m ipvs --vaddr 192.168.42.1/24 --vport 80 -j
> SNAT --to-source 192.168.10.10
Make sure /proc/sys/net/ipv4/vs/conntrack is set to 1
to allow IPVS to keep the netfilter conntracks for its
packets. This is supported with the CONFIG_IP_VS_NFCT=y
kernel option.
> What I'd expect: a packet outgoing from enp4s0 with source IP 192.168.10.10
> and destination IP 192.168.20.20
> What I see from a test client:
> - in l3 mode: a packet outgoing from enp4s0 with source client IP address and
> destination 192.168.20.20 (hence missing source NAT). I also don't see any
> conntrack event when doing conntrack -E
> - in l3s mode: connection reset sent to client. While reading l3s
> implementation, I wonder where route lookup is done in ipvlan_l3_rcv, it
> seems that namespaces' virtual IP addresses are not visible during this
> lookup, hence the TCP RST.
Regards
--
Julian Anastasov <ja@xxxxxx>
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