Align IP selection behavior with kernel

pkg/node/address_linux.go

@@ -6,7 +6,6 @@
 package node
 
 import (
-	"bytes"
 	"fmt"
 	"net"
 	"sort"
@@ -47,28 +46,37 @@ retryInterface:
 	}
 
 retryScope:
-	ipsPublic := []net.IP{}
-	ipsPrivate := []net.IP{}
+	ipsPublic := []netlink.Addr{}
+	ipsPrivate := []netlink.Addr{}
 	hasPreferred := false
 
 	for _, a := range addr {
-		if a.Scope <= linkScopeMax {
-			if ip.ListContainsIP(ipsToExclude, a.IP) {
-				continue
-			}
-			if len(a.IP) >= ipLen {
-				if ip.IsPublicAddr(a.IP) {
-					ipsPublic = append(ipsPublic, a.IP)
-				} else {
-					ipsPrivate = append(ipsPrivate, a.IP)
-				}
-				// If the IP is the same as the preferredIP, that
-				// means that maybe it is restored from node_config.h,
-				// so if it is present we prefer this one.
-				if a.IP.Equal(preferredIP) {
-					hasPreferred = true
-				}
-			}
+		if a.Scope > linkScopeMax {
+			continue
+		}
+		if ip.ListContainsIP(ipsToExclude, a.IP) {
+			continue
+		}
+		if len(a.IP) < ipLen {
+			continue
+		}
+		isPreferredIP := a.IP.Equal(preferredIP)
+		if a.Flags&unix.IFA_F_SECONDARY > 0 && !isPreferredIP {
+			// Skip secondary addresses if they're not the preferredIP
+			continue
+		}
+
+		if ip.IsPublicAddr(a.IP) {
+			ipsPublic = append(ipsPublic, a)
+		} else {
+			ipsPrivate = append(ipsPrivate, a)
+		}
+		// If the IP is the same as the preferredIP, that
+		// means that maybe it is restored from node_config.h,
+		// so if it is present we prefer this one, even if it
+		// is a secondary address.
+		if isPreferredIP {
+			hasPreferred = true
 		}
 	}
 
@@ -83,11 +91,11 @@ retryScope:
 
 		// Just make sure that we always return the same one and not a
 		// random one. More info in the issue GH-7637.
-		sort.Slice(ipsPublic, func(i, j int) bool {
-			return bytes.Compare(ipsPublic[i], ipsPublic[j]) < 0
+		sort.SliceStable(ipsPublic, func(i, j int) bool {
+			return ipsPublic[i].LinkIndex < ipsPublic[j].LinkIndex
 		})
 
-		return ipsPublic[0], nil
+		return ipsPublic[0].IP, nil
 	}
 
 	if len(ipsPrivate) != 0 {
@@ -96,11 +104,11 @@ retryScope:
 		}
 
 		// Same stable order, see above ipsPublic.
-		sort.Slice(ipsPrivate, func(i, j int) bool {
-			return bytes.Compare(ipsPrivate[i], ipsPrivate[j]) < 0
+		sort.SliceStable(ipsPrivate, func(i, j int) bool {
+			return ipsPrivate[i].LinkIndex < ipsPrivate[j].LinkIndex
 		})
 
-		return ipsPrivate[0], nil
+		return ipsPrivate[0].IP, nil
 	}
 
 	// First, if a device is specified, fall back to anything wider
@@ -123,7 +131,9 @@ retryScope:
 }
 
 // firstGlobalV4Addr returns the first IPv4 global IP of an interface,
-// where the IPs are sorted in ascending order.
+// where the IPs are sorted in creation order (oldest to newest).
+//
+// All secondary IPs, except the preferredIP, are filtered out.
 //
 // Public IPs are preferred over private ones. When intf is defined only
 // IPs belonging to that interface are considered.

pkg/node/address_linux_test.go

@@ -55,6 +55,11 @@ func (s *NodePrivilegedSuite) Test_firstGlobalV4Addr(c *C) {
 			preferredIP:    "192.168.0.1",
 			want:           "21.0.0.1",
 		},
+		{
+			name:           "primary IP preferred by default",
+			ipsOnInterface: []string{"192.168.0.2", "192.168.0.1"},
+			want:           "192.168.0.2",
+		},
 	}
 	const ifName = "dummy_iface"
 	for _, tc := range testCases {