Index: sys/dev/hyperv/netvsc/hv_netvsc_drv_freebsd.c
===================================================================
--- sys/dev/hyperv/netvsc/hv_netvsc_drv_freebsd.c
+++ sys/dev/hyperv/netvsc/hv_netvsc_drv_freebsd.c
@@ -128,6 +128,9 @@
 #define HV_NV_SC_PTR_OFFSET_IN_BUF         0
 #define HV_NV_PACKET_OFFSET_IN_BUF         16
 
+#define CSUM_FOR_OUTBOUND \
+    (CSUM_IP|CSUM_IP_UDP|CSUM_IP_TCP|CSUM_IP_SCTP|CSUM_IP_TSO|CSUM_IP_ISCSI| \
+     CSUM_IP6_UDP|CSUM_IP6_TCP|CSUM_IP6_SCTP|CSUM_IP6_TSO|CSUM_IP6_ISCSI)
 
 /*
  * Data types
@@ -570,7 +573,8 @@
 			    packet->vlan_tci & 0xfff;
 		}
 
-		if (0 == m_head->m_pkthdr.csum_flags) {
+		/* Ignore flags for checksum already calculated or valid */
+		if (0 == (m_head->m_pkthdr.csum_flags & CSUM_FOR_OUTBOUND)) {
 			goto pre_send;
 		}