chassis: Deprecate support for STT encapsulation.

STT tunnel support will be deprecated in upcoming OVS 3.5 release and planned for removal in OVS 3.6. The main reasons are: STT tunnel implementation was rejected in the upstream Linux kernel long time ago and will probably never be there, because it is not considered safe for use, as it can confuse parts of the network mistaking it for normal TCP. The only available implementation for Linux is an OOT openvswitch kernel module shipped with OVS 2.17. This module is deprecated and 2.17 reaches EoL in Feb 2025. At that point there will be no supported implementation for Linux. The standard draft for the protocol itself is also expired and archived with the latest update made in 2016: https://datatracker.ietf.org/doc/draft-davie-stt/ Modern network interface cards support various hardware offload features with UDP tunnels, diminishing the main selling point of STT - the ability to reuse hardware offload features meant for TCP. Deprecate the STT encapsulation type in OVN as well, so support can be removed in 25.09. Signed-off-by: Ilya Maximets <[email protected]> Acked-by: Ales Musil <[email protected]> Signed-off-by: Dumitru Ceara <[email protected]>
ovn-org · Dec 11, 2024 · 8a3981e · 8a3981e
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diff --git a/Documentation/faq/general.rst b/Documentation/faq/general.rst
@@ -88,6 +88,9 @@ Q: Why does OVN use STT and Geneve instead of VLANs or VXLAN (or GRE)?
 
     See ``ovn-architecture(7)``, under "Tunnel Encapsulations", for details.
 
+    Note: Support for STT tunnels is deprecated and will be removed in OVN
+    25.09 release.
+
     Together, these metadata require 24 + 15 + 16 = 55 bits.  GRE provides 32
     bits, VXLAN provides 24, and VLAN only provides 12.  Most notably, if
     logical egress pipelines do not match on the logical ingress port, thereby

diff --git a/NEWS b/NEWS
@@ -4,6 +4,8 @@ Post v24.09.0
      hash (with specified hash fields) for ECMP routes
      while choosing nexthop.
    - ovn-ic: Add support for route tag to prevent route learning.
+   - Support for STT tunnels in ovn-encap-type is deprecated and will be
+     removed in the next release.
 
 OVN v24.09.0 - 13 Sep 2024
 --------------------------

diff --git a/controller/chassis.c b/controller/chassis.c
@@ -243,12 +243,16 @@ chassis_parse_ovs_encap_type(const char *encap_type,
 {
     sset_from_delimited_string(encap_type_set, encap_type, ",");
 
+    static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
     const char *type;
 
     SSET_FOR_EACH (type, encap_type_set) {
-        if (!get_tunnel_type(type)) {
-            static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
+        uint32_t tun_type = get_tunnel_type(type);
+
+        if (!tun_type) {
             VLOG_INFO_RL(&rl, "Unknown tunnel type: %s", type);
+        } else if (tun_type == STT) {
+            VLOG_WARN_RL(&rl, "STT encapsulation type is deprecated");
         }
     }
 }

diff --git a/controller/ovn-controller.8.xml b/controller/ovn-controller.8.xml
@@ -168,6 +168,10 @@
           are <code>geneve</code>, <code>vxlan</code>, and <code>stt</code>.
         </p>
 
+        <p>
+          <code>stt</code> tunnel type is deprecated.
+        </p>
+
         <p>
           Due to the limited amount of metadata in <code>vxlan</code>,
           the capabilities and performance of connected gateways and

diff --git a/lib/ovn-util.h b/lib/ovn-util.h
@@ -332,7 +332,8 @@ hash_add_in6_addr(uint32_t hash, const struct in6_addr *addr)
  * least-preferred (lower number). */
 enum chassis_tunnel_type {
     GENEVE = 1 << 2,
-    STT    = 1 << 1,
+    STT    = 1 << 1,  /* NOTE: STT support is deprecated and will be removed
+                       *       in an upcoming release. */
     VXLAN  = 1 << 0
 };
 

diff --git a/ovn-architecture.7.xml b/ovn-architecture.7.xml
@@ -2897,10 +2897,9 @@
   </diagram>
 
   <p>
-    Environments whose NICs lack Geneve offload may prefer STT encapsulation
-    for performance reasons.  For STT encapsulation, OVN encodes all three
-    pieces of logical metadata in the STT 64-bit tunnel ID as follows, from MSB
-    to LSB:
+    Support for STT encapsulation is deprecated.  While using STT on setups
+    that didn't migrate to Geneve yet, OVN encodes all three pieces of logical
+    metadata in the STT 64-bit tunnel ID as follows, from MSB to LSB:
   </p>
 
   <diagram>

diff --git a/ovn-sb.xml b/ovn-sb.xml
@@ -479,7 +479,8 @@
     <column name="type">
       The encapsulation to use to transmit packets to this chassis.
       Hypervisors and gateways must use one of: <code>geneve</code>,
-      <code>vxlan</code>, or <code>stt</code>.
+      <code>vxlan</code>, or <code>stt</code>.  <code>stt</code> is
+      deprecated.
     </column>
 
     <column name="options">

diff --git a/tests/ovn-ic.at b/tests/ovn-ic.at
@@ -333,7 +333,7 @@ OVS_WAIT_UNTIL([ovn_as az2 ovn-sbctl show | grep "192.168.0.2"])
 ovs-vsctl set open . external_ids:ovn-encap-type="geneve,stt"
 OVS_WAIT_UNTIL([ovn_as az2 ovn-sbctl show | grep stt])
 
-OVN_CLEANUP_SBOX(gw2)
+OVN_CLEANUP_SBOX([gw2], ["/STT encapsulation type is deprecated/d"])
 OVN_CLEANUP_IC([az1], [az2])
 
 AT_CLEANUP