[ovs-dev] [PATCH ovn] northd: Provide the Gateway router option 'lb_force_snat_ip' to take router port ips.

Numan Siddique numans at ovn.org
Thu Feb 18 14:30:50 UTC 2021


On Wed, Feb 17, 2021 at 7:37 PM Mark Gray <mark.d.gray at redhat.com> wrote:
>
> Thanks Numan, some suggestions below!

Hi Mark G,

Thanks for the review.

PSB for a few comments.

>
> On 09/02/2021 18:44, numans at ovn.org wrote:
> > From: Numan Siddique <numans at ovn.org>
> >
> > When a Gateway router is configured with a load balancer
> > and it is also configured with options:lb_force_snat_ip=<IP>,
> > OVN after load balancing the destination IP to one of the
> > backend also does a NAT on the source ip with the
> > lb_force_snat_ip if the packet is destined to a load balancer
> > VIP.
> >
> > There is a problem with the snat of source ip to 'lb_force_snat_ip'
> > in one particular usecase.  When the packet enters the Gateway router
> > from a provider logical switch destined to the load balancer VIP,
> > then it is first load balanced to one of the backend and then
> > the source ip is snatted to 'lb_force_snat_ip'.  If the chosen
> > backend is reachable via the provider logical switch, then the
> > packet is hairpinned back and it may hit the wire with
> > the source ip 'lb_force_snat_ip'.  If 'lb_force_snat_ip' happens
> > to be an OVN internal IP then the packet may be dropped.
> >
> > This patch addresses this issue by providing the option to
> > set the option - 'lb_force_snat_ip=router_ip'.  If 'router_ip'
> > is set, then OVN will snat the load balanced packet to the
> > router ip of the logical router port which chosen as 'outport'
> > in lr_in_ip_routing stage.
>
> It almost feels like this should be the default behaviour?


Can you please elaborate more ? You mean ideally CMS should set
- router_ip ?


> >
> > Example.
> >
> > If the gateway router is
> >
> > ovn-nbctl show lr0
> > router 68f20092-5563-44b8-9ccb-b11de3e3a66c (lr0)
> >     port lr0-sw0
> >         mac: "00:00:00:00:ff:01"
> >         networks: ["10.0.0.1/24"]
> >     port lr0-public
> >         mac: "00:00:20:20:12:13"
> >         networks: ["172.168.0.100/24"]
> >
> > Then the below logical flows are added if 'lb_force_snat_ip'
> > is configured to 'router_ip'.
> >
> > table=1 (lr_out_snat), priority=110
> >    match=(flags.force_snat_for_lb == 1 && ip4 && outport == "lr0-public"),
> >    action=(ct_snat(172.168.0.100);)
> >
> > table=1 (lr_out_snat), priority=110
> >    match=(flags.force_snat_for_lb == 1 && ip4 && outport == "lr0-sw0")
> >    action=(ct_snat(10.0.0.1);)
> >
> > For the above described scenario, the packet will have source ip as
> > 172.168.0.100 which belongs to the provider logical switch CIDR.
> >
> > Reported-by: Tim Rozet <trozet at redhat.com>
> > Signed-off-by: Numan Siddique <numans at ovn.org>
> > ---
> >  northd/ovn-northd.8.xml | 35 ++++++++++++++++++
> >  northd/ovn-northd.c     | 66 ++++++++++++++++++++++++++++++++--
> >  tests/ovn-northd.at     | 79 +++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 177 insertions(+), 3 deletions(-)
> >
> > diff --git a/northd/ovn-northd.8.xml b/northd/ovn-northd.8.xml
> > index 70065a36d9..27b28aff93 100644
> > --- a/northd/ovn-northd.8.xml
> > +++ b/northd/ovn-northd.8.xml
>
> Should 'ovn-nb.xml' also be updated?

Great catch. I totally missed it.

>
> > @@ -3653,6 +3653,32 @@ nd_ns {
> >            <code>flags.force_snat_for_dnat == 1 && ip</code> with an
> >            action <code>ct_snat(<var>B</var>);</code>.
> >          </p>
> > +      </li>
> > +
> > +      <li>
> > +        <p>
> > +          If the Gateway router in the OVN Northbound database has been
> > +          configured to force SNAT a packet (that has been previously
> > +          load-balanced) using router IP (i.e <ref column="options"
> > +          table="Logical_Router"/>:lb_force_snat_ip=router_ip), then for
> > +          each logical router port <var>P</var> attached to the Gateway
> > +          router, a priority-110 flow matches
> > +          <code>flags.force_snat_for_lb == 1 && outport == <var>P</var>
> > +          </code> with an action <code>ct_snat(<var>R</var>);</code>
> > +          where <var>R</var> is the router port IP configured.
>
> maybe rephrase to "is the IP configured on the router port."

Ack. done

>
> > +          If <code>R</code> is an IPv4 address then the match will also
> > +          include <code>ip4</code> and if it is an IPv6 address, then the
> > +          match will also include <code>ip6</code>.
> > +        </p>
> > +
> > +        <p>
> > +          If the logical router port <var>P</var> is configured with multiple
> > +          IPv4 and multiple IPv6 addresses, only the first IPv4 and first IPv6
> > +          address is considered.
>
> Should we log this condition?

Ack. I have added the log for this in v2.


>
> > +        </p>
> > +      </li>
> > +
> > +      <li>
> >          <p>
> >            If the Gateway router in the OVN Northbound database has been
> >            configured to force SNAT a packet (that has been previously
> > @@ -3660,6 +3686,9 @@ nd_ns {
> >            <code>flags.force_snat_for_lb == 1 && ip</code> with an
> >            action <code>ct_snat(<var>B</var>);</code>.
> >          </p>
> > +      </li>
> > +
> > +      <li>
> >          <p>
> >            For each configuration in the OVN Northbound database, that asks
> >            to change the source IP address of a packet from an IP address of
> > @@ -3673,14 +3702,18 @@ nd_ns {
> >            options, then the action would be <code>ip4/6.src=
> >            (<var>B</var>)</code>.
> >          </p>
> > +      </li>
> >
> > +      <li>
> >          <p>
> >            If the NAT rule has <code>allowed_ext_ips</code> configured, then
> >            there is an additional match <code>ip4.dst == <var>allowed_ext_ips
> >            </var></code>. Similarly, for IPV6, match would be <code>ip6.dst ==
> >            <var>allowed_ext_ips</var></code>.
> >          </p>
> > +      </li>
> >
> > +      <li>
> >          <p>
> >            If the NAT rule has <code>exempted_ext_ips</code> set, then
> >            there is an additional flow configured at the priority + 1 of
> > @@ -3689,7 +3722,9 @@ nd_ns {
> >            </code>. This flow is used to bypass the ct_snat action for a packet
> >            which is destinted to <code>exempted_ext_ips</code>.
> >          </p>
> > +      </li>
> >
> > +      <li>
> >          <p>
> >            A priority-0 logical flow with match <code>1</code> has actions
> >            <code>next;</code>.
> > diff --git a/northd/ovn-northd.c b/northd/ovn-northd.c
> > index db6572a62b..ece158b71e 100644
> > --- a/northd/ovn-northd.c
> > +++ b/northd/ovn-northd.c
> > @@ -622,6 +622,7 @@ struct ovn_datapath {
> >
> >      struct lport_addresses dnat_force_snat_addrs;
> >      struct lport_addresses lb_force_snat_addrs;
> > +    bool lb_force_snat_router_ip;
> >
> >      struct ovn_port **localnet_ports;
> >      size_t n_localnet_ports;
> > @@ -721,6 +722,17 @@ init_nat_entries(struct ovn_datapath *od)
> >              snat_ip_add(od, od->lb_force_snat_addrs.ipv6_addrs[0].addr_s,
> >                          NULL);
> >          }
> > +    } else {
> > +        const char *lb_force_snat =
> > +            smap_get(&od->nbr->options, "lb_force_snat_ip");
> > +        if (lb_force_snat && !strcmp(lb_force_snat, "router_ip")
> > +                && smap_get(&od->nbr->options, "chassis")) {
> > +            /* Set it to true only if its gateway router and
> > +             * options:lb_force_snat_ip=router_ip. */
> > +            od->lb_force_snat_router_ip = true;
> > +        } else {
> > +            od->lb_force_snat_router_ip = false;
> > +        }
> >      }
> >
> >      if (!od->nbr->n_nat) {
> > @@ -8365,9 +8377,12 @@ get_force_snat_ip(struct ovn_datapath *od, const char *key_type,
> >      }
> >
> >      if (!extract_ip_address(addresses, laddrs)) {
> > -        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 1);
> > -        VLOG_WARN_RL(&rl, "bad ip %s in options of router "UUID_FMT"",
> > -                     addresses, UUID_ARGS(&od->key));
> > +        if (strcmp(addresses, "router_ip") || strcmp(key_type, "lb")) {
>
> Also, probably good to check or assert 'key_type' for NULL even though,
> currently, all callers of get_force_snat_ip() cant pass a NULL value.

In v2, (which I'll submit now), I'm not modifying this function at all.

Also if "key_type' is NULL, then the code above this , which is
----
char *key = xasprintf("%s_force_snat_ip", key_type);
const char *addresses = smap_get(&od->nbr->options, key);
-----
'addresses' will be NULL and hence we will not hit this condition.


> > +            static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 1);
> > +            VLOG_WARN_RL(&rl, "bad ip %s in options of router "UUID_FMT"",
> > +                         addresses, UUID_ARGS(&od->key));
> > +        }
> > +
> >          return false;
>
> I think finding an IP or 'router_ip' should be the successful case and
> not finding them should be unsuccessful. However, this would change the
> logic for callers. Or maybe the name of this function could change and
> another function to check for router_ip could be added. What do you think?

Ok. I get your point. My only reason to modify the function -
get_force_snat_ip()
was not to not log a warning if 'router_ip' is set. Ideally this
function should be called
if the option is a set of IP address(es).

So in v2, I've not modified this function. But instead I first check
if lb_force_snat_ip
is configured with 'router_ip' or not. I felt there is probably no
need for a function just
for that.

>
> >      }
> >
> > @@ -8943,6 +8958,48 @@ build_lrouter_force_snat_flows(struct hmap *lflows, struct ovn_datapath *od,
> >      ds_destroy(&actions);
> >  }
> >
> > +static void
> > +build_lrouter_force_snat_flows_op(struct ovn_port *op,
> > +                                  struct hmap *lflows,
> > +                                  struct ds *match, struct ds *actions)
> > +{
> > +    if (!op->nbrp || !op->peer || !op->od->lb_force_snat_router_ip) {
> > +        return;
> > +    }
> > +
> > +    if (op->lrp_networks.n_ipv4_addrs) {
> > +        ds_clear(match);
> > +        ds_clear(actions);
> > +
> > +        /* Higher priority rules to force SNAT with the router port ip.
> > +         * This only takes effect when the packet has already been
> > +         * load balanced once. */
> > +        ds_put_format(match, "flags.force_snat_for_lb == 1 && ip4 && "
> > +                      "outport == %s", op->json_key);
> > +        ds_put_format(actions, "ct_snat(%s);",
> > +                      op->lrp_networks.ipv4_addrs[0].addr_s);
> > +        ovn_lflow_add(lflows, op->od, S_ROUTER_OUT_SNAT, 110,
>
> General musing that doesn't need to be addressed here. I wonder should
> we have a macro definition for priorities for logical flows?

I'm not too sure. I think we could. But we will end up with lots of macros.

Please check out the v2.

Thanks
Numan

>
> > +                      ds_cstr(match), ds_cstr(actions));
> > +    }
> > +
> > +    /* op->lrp_networks.ipv6_addrs will always have LLA and that will be
> > +     * last in the list. So add the flows only if n_ipv6_addrs > 1. */
> > +    if (op->lrp_networks.n_ipv6_addrs > 1) {
> > +        ds_clear(match);
> > +        ds_clear(actions);
> > +
> > +        /* Higher priority rules to force SNAT with the router port ip.
> > +         * This only takes effect when the packet has already been
> > +         * load balanced once. */
> > +        ds_put_format(match, "flags.force_snat_for_lb == 1 && ip6 && "
> > +                      "outport == %s", op->json_key);
> > +        ds_put_format(actions, "ct_snat(%s);",
> > +                      op->lrp_networks.ipv6_addrs[0].addr_s);
> > +        ovn_lflow_add(lflows, op->od, S_ROUTER_OUT_SNAT, 110,
> > +                      ds_cstr(match), ds_cstr(actions));
> > +    }
> > +}
> > +
> >  static void
> >  build_lrouter_bfd_flows(struct hmap *lflows, struct ovn_port *op)
> >  {
> > @@ -11278,6 +11335,7 @@ build_lrouter_nat_defrag_and_lb(struct ovn_datapath *od,
> >                          "dnat");
> >                  }
> >              }
> > +
> >              if (lb_force_snat_ip) {
> >                  if (od->lb_force_snat_addrs.n_ipv4_addrs) {
> >                      build_lrouter_force_snat_flows(lflows, od, "4",
> > @@ -11490,6 +11548,8 @@ build_lswitch_and_lrouter_iterate_by_op(struct ovn_port *op,
> >                                              &lsi->match, &lsi->actions);
> >      build_lrouter_ipv4_ip_input(op, lsi->lflows,
> >                                  &lsi->match, &lsi->actions);
> > +    build_lrouter_force_snat_flows_op(op, lsi->lflows, &lsi->match,
> > +                                      &lsi->actions);
> >  }
> >
> >  static void
> > diff --git a/tests/ovn-northd.at b/tests/ovn-northd.at
> > index 7240e22baf..fd03b1fb66 100644
> > --- a/tests/ovn-northd.at
> > +++ b/tests/ovn-northd.at
> > @@ -2443,3 +2443,82 @@ check ovn-sbctl set chassis hv1 other_config:port-up-notif=true
> >  wait_row_count nb:Logical_Switch_Port 1 up=false name=lsp1
> >
> >  AT_CLEANUP
> > +
> > +AT_SETUP([ovn -- lb_force_snat_ip for Gateway Routers])
> > +ovn_start
> > +
> > +check ovn-nbctl ls-add sw0
> > +check ovn-nbctl ls-add sw1
> > +
> > +# Create a logical router and attach both logical switches
> > +check ovn-nbctl lr-add lr0
> > +check ovn-nbctl lrp-add lr0 lr0-sw0 00:00:00:00:ff:01 10.0.0.1/24
> > +check ovn-nbctl lsp-add sw0 sw0-lr0
> > +check ovn-nbctl lsp-set-type sw0-lr0 router
> > +check ovn-nbctl lsp-set-addresses sw0-lr0 00:00:00:00:ff:01
> > +check ovn-nbctl lsp-set-options sw0-lr0 router-port=lr0-sw0
> > +
> > +check ovn-nbctl lrp-add lr0 lr0-sw1 00:00:00:00:ff:02 20.0.0.1/24
> > +check ovn-nbctl lsp-add sw1 sw1-lr0
> > +check ovn-nbctl lsp-set-type sw1-lr0 router
> > +check ovn-nbctl lsp-set-addresses sw1-lr0 00:00:00:00:ff:02
> > +check ovn-nbctl lsp-set-options sw1-lr0 router-port=lr0-sw1
> > +
> > +check ovn-nbctl ls-add public
> > +check ovn-nbctl lrp-add lr0 lr0-public 00:00:20:20:12:13 172.168.0.100/24
> > +check ovn-nbctl lsp-add public public-lr0
> > +check ovn-nbctl lsp-set-type public-lr0 router
> > +check ovn-nbctl lsp-set-addresses public-lr0 router
> > +check ovn-nbctl lsp-set-options public-lr0 router-port=lr0-public
> > +
> > +check ovn-nbctl set logical_router lr0 options:chassis=ch1
> > +
> > +ovn-sbctl dump-flows lr0 > lr0flows
> > +AT_CAPTURE_FILE([lr0flows])
> > +
> > +AT_CHECK([grep "lr_out_snat" lr0flows | grep force_snat_for_lb | sort], [0], [dnl
> > +])
> > +
> > +check ovn-nbctl --wait=sb set logical_router lr0 options:lb_force_snat_ip="20.0.0.4 aef0::4"
> > +
> > +ovn-sbctl dump-flows lr0 > lr0flows
> > +AT_CAPTURE_FILE([lr0flows])
> > +
> > +AT_CHECK([grep "lr_out_snat" lr0flows | grep force_snat_for_lb | sort], [0], [dnl
> > +  table=1 (lr_out_snat        ), priority=100  , match=(flags.force_snat_for_lb == 1 && ip4), action=(ct_snat(20.0.0.4);)
> > +  table=1 (lr_out_snat        ), priority=100  , match=(flags.force_snat_for_lb == 1 && ip6), action=(ct_snat(aef0::4);)
> > +])
> > +
> > +check ovn-nbctl --wait=sb set logical_router lr0 options:lb_force_snat_ip="router_ip"
> > +
> > +ovn-sbctl dump-flows lr0 > lr0flows
> > +AT_CAPTURE_FILE([lr0flows])
> > +
> > +AT_CHECK([grep "lr_out_snat" lr0flows | grep force_snat_for_lb | sort], [0], [dnl
> > +  table=1 (lr_out_snat        ), priority=110  , match=(flags.force_snat_for_lb == 1 && ip4 && outport == "lr0-public"), action=(ct_snat(172.168.0.100);)
> > +  table=1 (lr_out_snat        ), priority=110  , match=(flags.force_snat_for_lb == 1 && ip4 && outport == "lr0-sw0"), action=(ct_snat(10.0.0.1);)
> > +  table=1 (lr_out_snat        ), priority=110  , match=(flags.force_snat_for_lb == 1 && ip4 && outport == "lr0-sw1"), action=(ct_snat(20.0.0.1);)
> > +])
> > +
> > +check ovn-nbctl --wait=sb remove logical_router lr0 options chassis
> > +
> > +ovn-sbctl dump-flows lr0 > lr0flows
> > +AT_CAPTURE_FILE([lr0flows])
> > +
> > +AT_CHECK([grep "lr_out_snat" lr0flows | grep force_snat_for_lb | sort], [0], [dnl
> > +])
> > +
> > +check ovn-nbctl set logical_router lr0 options:chassis=ch1
> > +check ovn-nbctl --wait=sb add logical_router_port lr0-sw1 networks "bef0\:\:1/64"
> > +
> > +ovn-sbctl dump-flows lr0 > lr0flows
> > +AT_CAPTURE_FILE([lr0flows])
> > +
> > +AT_CHECK([grep "lr_out_snat" lr0flows | grep force_snat_for_lb | sort], [0], [dnl
> > +  table=1 (lr_out_snat        ), priority=110  , match=(flags.force_snat_for_lb == 1 && ip4 && outport == "lr0-public"), action=(ct_snat(172.168.0.100);)
> > +  table=1 (lr_out_snat        ), priority=110  , match=(flags.force_snat_for_lb == 1 && ip4 && outport == "lr0-sw0"), action=(ct_snat(10.0.0.1);)
> > +  table=1 (lr_out_snat        ), priority=110  , match=(flags.force_snat_for_lb == 1 && ip4 && outport == "lr0-sw1"), action=(ct_snat(20.0.0.1);)
> > +  table=1 (lr_out_snat        ), priority=110  , match=(flags.force_snat_for_lb == 1 && ip6 && outport == "lr0-sw1"), action=(ct_snat(bef0::1);)
> > +])
> > +
> > +AT_CLEANUP
> >
>
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