ofproto-dpif: Do not mirror L2 multicast switch protocols to VLANs.

Mirroring certain protocols interpreted by switches to a VLAN can deceive
the switch that receives it.  Drop such packets instead of mirroring them.

CC: David Tsai <dtsai@nicira.com>
NIC-401.

2 files changed, 73 insertions, 1 deletions

diff --git a/vswitchd/bridge.c b/vswitchd/bridge.c
index 928d03ce3..86c50407e 100644
--- a/vswitchd/bridge.c
+++ b/vswitchd/bridge.c
@@ -2702,6 +2702,47 @@ port_is_floodable(const struct port *port)
     return true;
 }
 
+/* Returns true if a packet with Ethernet destination MAC 'dst' may be mirrored
+ * to a VLAN.  In general most packets may be mirrored but we want to drop
+ * protocols that may confuse switches. */
+static bool
+eth_dst_may_rspan(const uint8_t dst[ETH_ADDR_LEN])
+{
+    /* If you change this function's behavior, please update corresponding
+     * documentation in vswitch.xml at the same time. */
+    if (dst[0] != 0x01) {
+        /* All the currently banned MACs happen to start with 01 currently, so
+         * this is a quick way to eliminate most of the good ones. */
+    } else {
+        if (eth_addr_is_reserved(dst)) {
+            /* Drop STP, IEEE pause frames, and other reserved protocols
+             * (01-80-c2-00-00-0x). */
+            return false;
+        }
+
+        if (dst[0] == 0x01 && dst[1] == 0x00 && dst[2] == 0x0c) {
+            /* Cisco OUI. */
+            if ((dst[3] & 0xfe) == 0xcc &&
+                (dst[4] & 0xfe) == 0xcc &&
+                (dst[5] & 0xfe) == 0xcc) {
+                /* Drop the following protocols plus others following the same
+                   pattern:
+
+                   CDP, VTP, DTP, PAgP  (01-00-0c-cc-cc-cc)
+                   Spanning Tree PVSTP+ (01-00-0c-cc-cc-cd)
+                   STP Uplink Fast      (01-00-0c-cd-cd-cd) */
+                return false;
+            }
+
+            if (!(dst[3] | dst[4] | dst[5])) {
+                /* Drop Inter Switch Link packets (01-00-0c-00-00-00). */
+                return false;
+            }
+        }
+    }
+    return true;
+}
+
 static void
 compose_dsts(const struct bridge *br, const struct flow *flow, uint16_t vlan,
              const struct port *in_port, const struct port *out_port,
@@ -2744,7 +2785,7 @@ compose_dsts(const struct bridge *br, const struct flow *flow, uint16_t vlan,
                     && !dst_is_duplicate(set, &dst)) {
                     dst_set_add(set, &dst);
                 }
-            } else {
+            } else if (eth_dst_may_rspan(flow->dl_dst)) {
                 for (i = 0; i < br->n_ports; i++) {
                     struct port *port = br->ports[i];
                     if (port_includes_vlan(port, m->out_vlan)
diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
index 5c532e56f..2f7766918 100644
--- a/vswitchd/vswitch.xml
+++ b/vswitchd/vswitch.xml
@@ -1586,6 +1586,37 @@
           <ref column="output_vlan"/>, replacing any existing tag; when it is
           sent out an implicit VLAN port, the frame will not be tagged.  This
           type of mirroring is sometimes called RSPAN.</p>
+        <p>
+          The following destination MAC addresses will not be mirrored to a
+          VLAN to avoid confusing switches that interpret the protocols that
+          they represent:
+        </p>
+        <dl>
+          <dt><code>01:80:c2:00:00:00</code></dt>
+          <dd>IEEE 802.1D Spanning Tree Protocol (STP).</dd>
+
+          <dt><code>01:80:c2:00:00:01</code></dt>
+          <dd>IEEE Pause frame.</dd>
+
+          <dt><code>01:80:c2:00:00:0<var>x</var></code></dt>
+          <dd>Other reserved protocols.</dd>
+
+          <dt><code>01:00:0c:cc:cc:cc</code></dt>
+          <dd>
+            Cisco Discovery Protocol (CDP), VLAN Trunking Protocol (VTP),
+            Dynamic Trunking Protocol (DTP), Port Aggregation Protocol (PAgP),
+            and others.
+          </dd>
+
+          <dt><code>01:00:0c:cc:cc:cd</code></dt>
+          <dd>Cisco Shared Spanning Tree Protocol PVSTP+.</dd>
+
+          <dt><code>01:00:0c:cd:cd:cd</code></dt>
+          <dd>Cisco STP Uplink Fast.</dd>
+
+          <dt><code>01:00:0c:00:00:00</code></dt>
+          <dd>Cisco Inter Switch Link.</dd>
+        </dl>
         <p><em>Please note:</em> Mirroring to a VLAN can disrupt a network that
           contains unmanaged switches.  Consider an unmanaged physical switch
           with two ports: port 1, connected to an end host, and port 2,