diff --git a/share/man/man4/epair.4 b/share/man/man4/epair.4
--- a/share/man/man4/epair.4
+++ b/share/man/man4/epair.4
@@ -25,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd March 18, 2015
+.Dd July 30, 2025
 .Dt EPAIR 4
 .Os
 .Sh NAME
@@ -96,6 +96,21 @@
 can have a
 .Xr vlan 4
 configured on top of it.
+.Pp
+The
+.Nm
+supports TXCSUM and TXCSUM6 for TCP and UDP,
+but only by forwarding the order to compute the checksum.
+Thus, when using an
+.Nm
+interface, a TCP or UDP sender can offload checksum computation
+to a physical interface.
+Note that, in case the packet does not leave the host, the checksum is
+unnecessary and will be ignored if offloaded.
+TXCSUM and TXCSUM6 are synchronized between the
+.Nm
+interface pair (i.e., enabling/disabling the capability on one end
+enables/disables it on the other end).
 .Sh SEE ALSO
 .Xr ioctl 2 ,
 .Xr altq 4 ,
diff --git a/sys/net/if_epair.c b/sys/net/if_epair.c
--- a/sys/net/if_epair.c
+++ b/sys/net/if_epair.c
@@ -66,9 +66,9 @@
 #include <net/if_var.h>
 #include <net/if_clone.h>
 #include <net/if_media.h>
-#include <net/if_var.h>
 #include <net/if_private.h>
 #include <net/if_types.h>
+#include <net/if_vlan_var.h>
 #include <net/netisr.h>
 #ifdef RSS
 #include <net/rss_config.h>
@@ -96,6 +96,7 @@
 #define	EPAIR_LOCK_DESTROY()		mtx_destroy(&epair_n_index_mtx)
 #define	EPAIR_LOCK()			mtx_lock(&epair_n_index_mtx)
 #define	EPAIR_UNLOCK()			mtx_unlock(&epair_n_index_mtx)
+#define	EPAIR_LOCK_ASSERT()		mtx_assert(&epair_n_index_mtx, MA_OWNED);
 
 struct epair_softc;
 struct epair_queue {
@@ -425,6 +426,23 @@
 	imr->ifm_active = IFM_ETHER | IFM_10G_T | IFM_FDX;
 }
 
+/*
+ * To be called under EPAIR_LOCK. Update ifp->if_hwassist according to the
+ * current value of ifp->if_capenable.
+ */
+static void
+epair_caps_changed(struct ifnet *ifp)
+{
+	uint64_t hwassist = 0;
+
+	EPAIR_LOCK_ASSERT();
+	if (ifp->if_capenable & IFCAP_TXCSUM)
+		hwassist |= CSUM_IP_TCP | CSUM_IP_UDP;
+	if (ifp->if_capenable & IFCAP_TXCSUM_IPV6)
+		hwassist |= CSUM_IP6_TCP | CSUM_IP6_UDP;
+	ifp->if_hwassist = hwassist;
+}
+
 static int
 epair_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 {
@@ -452,6 +470,33 @@
 		error = 0;
 		break;
 
+	case SIOCGIFCAP:
+		ifr->ifr_reqcap = ifp->if_capabilities;
+		ifr->ifr_curcap = ifp->if_capenable;
+		error = 0;
+		break;
+	case SIOCSIFCAP:
+		sc = ifp->if_softc;
+		EPAIR_LOCK();
+		ifp->if_capenable = ifr->ifr_reqcap;
+		epair_caps_changed(ifp);
+		/*
+		 * If IFCAP_TXCSUM(_IPV6) has been changed, change it on the
+		 * other epair interface as well.
+		 */
+		if ((ifp->if_capenable ^ sc->oifp->if_capenable) &
+		    (IFCAP_TXCSUM | IFCAP_TXCSUM_IPV6)) {
+			sc->oifp->if_capenable &=
+			    ~(IFCAP_TXCSUM | IFCAP_TXCSUM_IPV6);
+			sc->oifp->if_capenable |= ifp->if_capenable &
+			    (IFCAP_TXCSUM | IFCAP_TXCSUM_IPV6);
+			epair_caps_changed(sc->oifp);
+		}
+		EPAIR_UNLOCK();
+		VLAN_CAPABILITIES(ifp);
+		error = 0;
+		break;
+
 	default:
 		/* Let the common ethernet handler process this. */
 		error = ether_ioctl(ifp, cmd, data);
@@ -549,8 +594,12 @@
 	ifp->if_dname = epairname;
 	ifp->if_dunit = unit;
 	ifp->if_flags = IFF_BROADCAST | IFF_SIMPLEX | IFF_MULTICAST;
-	ifp->if_capabilities = IFCAP_VLAN_MTU;
+	EPAIR_LOCK();
+	ifp->if_capabilities = IFCAP_VLAN_MTU | IFCAP_TXCSUM |
+	    IFCAP_TXCSUM_IPV6 | IFCAP_RXCSUM | IFCAP_RXCSUM_IPV6;
 	ifp->if_capenable = IFCAP_VLAN_MTU;
+	epair_caps_changed(ifp);
+	EPAIR_UNLOCK();
 	ifp->if_transmit = epair_transmit;
 	ifp->if_qflush = epair_qflush;
 	ifp->if_start = epair_start;