From f77e84806724b7f1bb6874c98a8827f1f50911c7 Mon Sep 17 00:00:00 2001
From: Nischal Sheth <nsheth@juniper.net>
Date: Sun, 18 Oct 2015 17:05:20 -0700
Subject: [PATCH] Retain MED when advertising XMPP originated routes to eBGP
 peers

Change-Id: I8ce50449f1f4d2b4d5fe8548856501e8bac9e4d4
Closes-Bug: 1501412
---
 src/bgp/bgp_table.cc                  |  9 +++-
 src/bgp/test/bgp_table_export_test.cc | 73 +++++++++++++++++++++++++--
 2 files changed, 75 insertions(+), 7 deletions(-)

diff --git a/src/bgp/bgp_table.cc b/src/bgp/bgp_table.cc
index 707578df3fd..d8f6a666386 100644
--- a/src/bgp/bgp_table.cc
+++ b/src/bgp/bgp_table.cc
@@ -213,9 +213,14 @@ UpdateInfo *BgpTable::GetUpdateInfo(RibOut *ribout, BgpRoute *route,
             if (attr->local_pref())
                 clone->set_local_pref(0);
 
-            // Reset Med if the path was not learnt from XMPP.
-            if (attr->med() && (!peer || peer->PeerType() != BgpProto::XMPP))
+            // Reset Med if the path did not originate from an xmpp peer.
+            // The AS path is NULL if the originating xmpp peer is locally
+            // connected. It's non-NULL but empty if the originating xmpp
+            // peer is connected to another bgp speaker in the iBGP mesh.
+            if (attr->med() && attr->as_path() &&
+                !attr->as_path()->path().path_segments.empty()) {
                 clone->set_med(0);
+            }
 
             // Prepend the local AS to AsPath.
             as_t local_as =
diff --git a/src/bgp/test/bgp_table_export_test.cc b/src/bgp/test/bgp_table_export_test.cc
index b7a41d4003b..67c17394114 100644
--- a/src/bgp/test/bgp_table_export_test.cc
+++ b/src/bgp/test/bgp_table_export_test.cc
@@ -191,6 +191,7 @@ class BgpTableExportTest : public ::testing::Test {
         if (internal_) {
             attr_spec.push_back(&path_spec);
             attr_spec.push_back(&local_pref);
+            attr_spec.push_back(&med);
         } else {
             AsPathSpec::PathSegment *path_seg = new AsPathSpec::PathSegment;
             path_seg->path_segment_type = AsPathSpec::PathSegment::AS_SEQUENCE;
@@ -462,15 +463,14 @@ TEST_P(BgpTableExportParamTest1, CommunityNoExportSubconfed) {
 // Table : inet.0, bgp.l3vpn.0
 // Source: eBGP, iBGP
 // RibOut: eBGP
-// Intent: LocalPref and Med are cleared for eBGP.
+// Intent: LocalPref is cleared for eBGP.
 //
-TEST_P(BgpTableExportParamTest1, EBgpNoLocalPrefMed) {
+TEST_P(BgpTableExportParamTest1, EBgpNoLocalPref) {
     CreateRibOut(BgpProto::EBGP, RibExportPolicy::BGP, 300);
     AddPath();
     RunExport();
     VerifyExportAccept();
     VerifyAttrLocalPref(0);
-    VerifyAttrMed(0);
 }
 
 //
@@ -486,7 +486,6 @@ TEST_P(BgpTableExportParamTest1, EBgpAsPrepend1) {
     RunExport();
     VerifyExportAccept();
     VerifyAttrLocalPref(0);
-    VerifyAttrMed(0);
     VerifyAttrAsPrepend();
 }
 
@@ -504,7 +503,6 @@ TEST_P(BgpTableExportParamTest1, EBgpAsPrepend2) {
     RunExport();
     VerifyExportAccept();
     VerifyAttrLocalPref(0);
-    VerifyAttrMed(0);
     VerifyAttrAsPrepend();
 }
 
@@ -558,6 +556,55 @@ TEST_P(BgpTableExportParamTest2, IBgpSplitHorizon) {
     VerifyExportReject();
 }
 
+//
+// Table : inet.0, bgp.l3vpn.0
+// Source: iBGP (effectively XMPP since AsPath is NULL)
+// RibOut: eBGP
+// Intent: Med is retained if AsPath is NULL.
+//
+TEST_P(BgpTableExportParamTest2, EBgpRetainMed1) {
+    CreateRibOut(BgpProto::EBGP, RibExportPolicy::BGP, 300);
+    ResetAttrAsPath();
+    AddPath();
+    RunExport();
+    VerifyExportAccept();
+    VerifyAttrLocalPref(0);
+    VerifyAttrMed(100);
+    VerifyAttrAsPrepend();
+}
+//
+// Table : inet.0, bgp.l3vpn.0
+// Source: iBGP
+// RibOut: eBGP
+// Intent: Med is retained if AsPath is non-NULL but empty.
+//
+TEST_P(BgpTableExportParamTest2, EBgpRetainMed2) {
+    CreateRibOut(BgpProto::EBGP, RibExportPolicy::BGP, 300);
+    AddPath();
+    RunExport();
+    VerifyExportAccept();
+    VerifyAttrLocalPref(0);
+    VerifyAttrMed(100);
+    VerifyAttrAsPrepend();
+}
+
+//
+// Table : inet.0, bgp.l3vpn.0
+// Source: iBGP
+// RibOut: eBGP
+// Intent: Med is not retained since AsPath is non-empty.
+//
+TEST_P(BgpTableExportParamTest2, EBgpNoRetainMed) {
+    CreateRibOut(BgpProto::EBGP, RibExportPolicy::BGP, 300);
+    SetAttrAsPath(100);
+    AddPath();
+    RunExport();
+    VerifyExportAccept();
+    VerifyAttrLocalPref(0);
+    VerifyAttrMed(0);
+    VerifyAttrAsPrepend();
+}
+
 INSTANTIATE_TEST_CASE_P(Instance, BgpTableExportParamTest2,
     ::testing::Values("inet.0", "bgp.l3vpn.0"));
 
@@ -688,6 +735,22 @@ TEST_P(BgpTableExportParamTest3, IBgpNoOverwriteMed) {
     VerifyAttrMed(100);
 }
 
+//
+// Table : inet.0, bgp.l3vpn.0
+// Source: eBGP
+// RibOut: eBGP
+// Intent: Med is not retained since AsPath is non-empty.
+//
+TEST_P(BgpTableExportParamTest3, EBgpNoRetainMed) {
+    CreateRibOut(BgpProto::EBGP, RibExportPolicy::BGP, 300);
+    AddPath();
+    RunExport();
+    VerifyExportAccept();
+    VerifyAttrLocalPref(0);
+    VerifyAttrMed(0);
+    VerifyAttrAsPrepend();
+}
+
 INSTANTIATE_TEST_CASE_P(Instance, BgpTableExportParamTest3,
     ::testing::Combine(
         ::testing::Values("inet.0", "bgp.l3vpn.0"),