*** src/sys/netinet/ip_fil.c    Sat May 27 12:40:44 2000
--- /tmp/ip_fil.c       Sat Aug 19 18:56:16 2000
***************
*** 1185,1190 ****
--- 1185,1194 ----
icmp->icmp_type = type;
icmp->icmp_code = fin->fin_icode;
icmp->icmp_cksum = 0;
+       if (type == ICMP_UNREACH &&
+               fin->fin_icode == ICMP_UNREACH_NEEDFRAG && ifp)
+               icmp->icmp_nextmtu = htons(((struct ifnet *) ifp)->if_mtu);
+ 
        if (avail) {
                bcopy((char *)oip, (char *)&icmp->icmp_ip, MIN(ohlen, avail));
                avail -= MIN(ohlen, avail);