Announce all IP addresses on error

Don't let the first error shortcut the announcement of subsequent
addresses. Loop over all addresses, and return the joined errors. Note
that the caller anyway ignores the error and only uses it for debug
logging.

pkg/utils/packet.go

@@ -3,6 +3,7 @@ package utils
 import (
 	"bytes"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"net"
 	"syscall"
@@ -164,7 +165,11 @@ func SendUnsolicitedNeighborAdvertisement(srcIP net.IP, linkObj netlink.Link) er
 	return nil
 }
 
-// AnnounceIPs sends either a GARP or Unsolicited NA depending on the IP address type (IPv4 vs. IPv6 respectively) configured on the interface.
+// AnnounceIPs sends IPv4 GARP and IPv6 Unsolicited NA for the addresses on the
+// interfaces.  If ifName is not found or has no MAC address, an error is
+// returned. If sending of announcements fail, the returned error is a combined
+// errors.Join() of each failed announcement. Despite such errors, remaining
+// addresses are still attempted to be announced.
 func AnnounceIPs(ifName string, ipConfigs []*current.IPConfig) error {
 	// Retrieve the interface name in the container.
 	linkObj, err := netLinkLib.LinkByName(ifName)
@@ -175,26 +180,27 @@ func AnnounceIPs(ifName string, ipConfigs []*current.IPConfig) error {
 		return fmt.Errorf("invalid Ethernet MAC address: %q", linkObj.Attrs().HardwareAddr)
 	}
 
+	var errResult error
+
 	// For all the IP addresses assigned by IPAM, we will send either a GARP (IPv4) or Unsolicited NA (IPv6).
 	for _, ipc := range ipConfigs {
-		var err error
-		if IsIPv6(ipc.Address.IP) {
+		if IsIPv4(ipc.Address.IP) {
+			err := SendGratuitousArp(ipc.Address.IP, linkObj)
+			if err != nil {
+				errResult = errors.Join(errResult, fmt.Errorf("failed to send GARP message for ip %s on interface %q: %v", ipc.Address.IP.String(), ifName, err))
+			}
+		} else if IsIPv6(ipc.Address.IP) {
 			/* As per RFC 4861, sending unsolicited neighbor advertisements should be considered as a performance
 			* optimization. It does not reliably update caches in all nodes. The Neighbor Unreachability Detection
 			* algorithm is more reliable although it may take slightly longer to update.
 			 */
-			err = SendUnsolicitedNeighborAdvertisement(ipc.Address.IP, linkObj)
-		} else if IsIPv4(ipc.Address.IP) {
-			err = SendGratuitousArp(ipc.Address.IP, linkObj)
-		} else {
-			return fmt.Errorf("the IP %s on interface %q is neither IPv4 or IPv6", ipc.Address.IP.String(), ifName)
-		}
-
-		if err != nil {
-			return fmt.Errorf("failed to send GARP/NA message for ip %s on interface %q: %v", ipc.Address.IP.String(), ifName, err)
+			err := SendUnsolicitedNeighborAdvertisement(ipc.Address.IP, linkObj)
+			if err != nil {
+				errResult = errors.Join(errResult, fmt.Errorf("failed to send NA message for ip %s on interface %q: %v", ipc.Address.IP.String(), ifName, err))
+			}
 		}
 	}
-	return nil
+	return errResult
 }
 
 // Blocking wait for interface ifName to have carrier (!NO_CARRIER flag).