Use ethernet tag as label if encapsulation is VXLAN

Note that we still encode/decode the label as a 20-bit value
in this release.

This provides backward compatibility with older 2.0 releases
and forward compatibility with 2.20 and newer releases. Note
that all releases set the VNI as the ethernet tag.

Change-Id: I60cdae79cf4a8b60ebb9ed271ccafca4193d4a91
Closes-Bug: 1464781

src/bgp/bgp_attr_base.cc

@@ -12,16 +12,32 @@ const size_t BgpProtoPrefix::kLabelSize = 3;
 BgpProtoPrefix::BgpProtoPrefix() : prefixlen(0), type(0) {
 }
 
-uint32_t BgpProtoPrefix::ReadLabel(size_t label_offset) const {
+//
+// Extract the label from the BgpProtorefix.
+// EVPN extensions for VXLAN use the label to convey a 24-bit VNI.
+//
+uint32_t BgpProtoPrefix::ReadLabel(size_t label_offset, bool is_vni) const {
     assert((label_offset + kLabelSize) <= prefix.size());
+    if (is_vni)
+        return get_value(&prefix[label_offset], kLabelSize);
     uint32_t label = (prefix[label_offset] << 16 |
         prefix[label_offset + 1] << 8 |
         prefix[label_offset + 2]) >> 4;
     return label;
 }
 
-void BgpProtoPrefix::WriteLabel(size_t label_offset, uint32_t label) {
+//
+// Write the label to the BgpProtorefix.
+// EVPN extensions for VXLAN use the label to convey a 24-bit VNI.
+//
+void BgpProtoPrefix::WriteLabel(size_t label_offset, uint32_t label,
+    bool is_vni) {
     assert((label_offset + kLabelSize) <= prefix.size());
+    if (is_vni) {
+        assert(label <= 0xFFFFFF);
+        put_value(&prefix[label_offset], kLabelSize, label);
+        return;
+    }
     assert(label <= 0xFFFFF);
     uint32_t tmp = (label << 4 | 0x1);
     for (size_t idx = 0; idx < kLabelSize; ++idx) {

src/bgp/bgp_attr_base.h

@@ -94,8 +94,8 @@ struct BgpProtoPrefix : public ParseObject {
 
     BgpProtoPrefix();
 
-    uint32_t ReadLabel(size_t label_offset) const;
-    void WriteLabel(size_t label_offset, uint32_t label);
+    uint32_t ReadLabel(size_t label_offset, bool is_vni = false) const;
+    void WriteLabel(size_t label_offset, uint32_t label, bool is_vni = false);
 
     std::vector<uint8_t> prefix;
     int prefixlen;

src/bgp/community.cc

@@ -212,6 +212,20 @@ vector<string> ExtCommunity::GetTunnelEncap() const {
     return encap_list;
 }
 
+bool ExtCommunity::ContainsTunnelEncapVxlan() const {
+    for (ExtCommunityList::const_iterator iter = communities_.begin();
+         iter != communities_.end(); ++iter) {
+        if (!ExtCommunity::is_tunnel_encap(*iter))
+            continue;
+        TunnelEncap encap(*iter);
+        if (encap.tunnel_encap() == TunnelEncapType::VXLAN)
+            return true;
+        if (encap.tunnel_encap() == TunnelEncapType::VXLAN_CONTRAIL)
+            return true;
+    }
+    return false;
+}
+
 ExtCommunity::ExtCommunity(ExtCommunityDB *extcomm_db,
         const ExtCommunitySpec spec) : extcomm_db_(extcomm_db) {
     refcount_ = 0;

src/bgp/community.h

@@ -163,6 +163,7 @@ class ExtCommunity {
     }
 
     std::vector<std::string> GetTunnelEncap() const;
+    bool ContainsTunnelEncapVxlan() const;
 
     static bool is_origin_vn(const ExtCommunityValue &val) {
         //

src/bgp/evpn/evpn_route.cc

@@ -34,6 +34,33 @@ const size_t EvpnPrefix::kMinInclusiveMulticastRouteSize =
 const size_t EvpnPrefix::kMinSegmentRouteSize =
     kRdSize + kEsiSize + 1;
 
+//
+// Read label from the BgpProtoPrefix.
+// If the encapsulation is VXLAN and ethernet tag is non-zero use that as
+// the label for backward compatibility with older JUNOS code and forward
+// compatibility with newer JUNOS and Contrail code which encodes/decodes
+// the label as a 24-bit value.
+//
+static uint32_t ReadLabel(const BgpProtoPrefix &proto_prefix,
+    const BgpAttr *attr, size_t offset, uint32_t tag) {
+    if (!attr)
+        return 0;
+    const ExtCommunity *extcomm = attr->ext_community();
+    if (extcomm && extcomm->ContainsTunnelEncapVxlan()) {
+        return (tag ? tag : proto_prefix.ReadLabel(offset, false));
+    } else {
+        return proto_prefix.ReadLabel(offset, false);
+    }
+}
+
+//
+// Write label to the BgpProtoPrefix.
+//
+static void WriteLabel(BgpProtoPrefix *proto_prefix,
+    const BgpAttr *attr, size_t offset, uint32_t label) {
+    proto_prefix->WriteLabel(offset, label, false);
+}
+
 EvpnPrefix::EvpnPrefix()
     : type_(Unspecified), tag_(EvpnPrefix::kNullTag), family_(Address::UNSPEC) {
 }
@@ -111,10 +138,8 @@ int EvpnPrefix::FromProtoPrefix(BgpServer *server,
         prefix->esi_ = EthernetSegmentId(&proto_prefix.prefix[esi_offset]);
         size_t tag_offset = esi_offset + kEsiSize;
         prefix->tag_ = get_value(&proto_prefix.prefix[tag_offset], kTagSize);
-        if (attr) {
-            size_t label_offset = tag_offset + kTagSize;
-            *label = proto_prefix.ReadLabel(label_offset);
-        }
+        size_t label_offset = tag_offset + kTagSize;
+        *label = ReadLabel(proto_prefix, attr, label_offset, prefix->tag_);
         break;
     }
     case MacAdvertisementRoute: {
@@ -146,10 +171,8 @@ int EvpnPrefix::FromProtoPrefix(BgpServer *server,
             return -1;
         size_t ip_offset = ip_len_offset + 1;
         prefix->ReadIpAddress(proto_prefix, ip_offset, ip_size);
-        if (attr) {
-            size_t label_offset = ip_offset + ip_size;
-            *label = proto_prefix.ReadLabel(label_offset);
-        }
+        size_t label_offset = ip_offset + ip_size;
+        *label = ReadLabel(proto_prefix, attr, label_offset, prefix->tag_);
         break;
     }
     case InclusiveMulticastRoute: {
@@ -229,7 +252,7 @@ void EvpnPrefix::BuildProtoPrefix(const BgpAttr *attr, uint32_t label,
         size_t tag_offset = esi_offset + kEsiSize;
         put_value(&proto_prefix->prefix[tag_offset], kTagSize, tag_);
         size_t label_offset = tag_offset + kTagSize;
-        proto_prefix->WriteLabel(label_offset, label);
+        WriteLabel(proto_prefix, attr, label_offset, label);
         break;
     }
     case MacAdvertisementRoute: {
@@ -258,7 +281,7 @@ void EvpnPrefix::BuildProtoPrefix(const BgpAttr *attr, uint32_t label,
         size_t ip_offset = ip_len_offset + 1;
         WriteIpAddress(proto_prefix, ip_offset);
         size_t label_offset = ip_offset + ip_size;
-        proto_prefix->WriteLabel(label_offset, label);
+        WriteLabel(proto_prefix, attr, label_offset, label);
         break;
     }
     case InclusiveMulticastRoute: {