Index: net-mgmt/net-snmp/Makefile
===================================================================
--- net-mgmt/net-snmp/Makefile
+++ net-mgmt/net-snmp/Makefile
@@ -139,6 +139,7 @@
 # --with-transport="UDPIPv6 TCPIPv6" --with-modules=mibII/ipv6"
 PLIST_SUB+=	WITH_IPV6=""
 .else
+CONFIGURE_ARGS+=--disable-ipv6
 PLIST_SUB+=	WITH_IPV6="@comment "
 .endif
 
Index: net-mgmt/net-snmp/files/patch-agent_mibgroup_udp-mib_data_access_udp_endpoint_freebsd4.c
===================================================================
--- /dev/null
+++ net-mgmt/net-snmp/files/patch-agent_mibgroup_udp-mib_data_access_udp_endpoint_freebsd4.c
@@ -0,0 +1,11 @@
+--- agent/mibgroup/udp-mib/data_access/udp_endpoint_freebsd4.c.orig	2020-12-23 13:33:48.723817000 +0000
++++ agent/mibgroup/udp-mib/data_access/udp_endpoint_freebsd4.c	2020-12-23 19:20:39.910144000 +0000
+@@ -155,6 +155,8 @@
+ #if !defined(NETSNMP_ENABLE_IPV6)
+ #ifdef INP_ISIPV6
+         if (INP_ISIPV6(&pcb.xi_inp))
++#elif __FreeBSD_version >= 1200026
++	if (pcb.inp_vflag & INP_IPV6)
+ #else
+         if (pcb.xi_inp.inp_vflag & INP_IPV6)
+ #endif