The wavelan/prism hardware can handle larger packets ..  And if you
are using IPsec to secure a wireless network, it's nice not to have
the overhead get in the way.  My scenario is like this:

Network/PC <-> Soekris <--802.11--> Soekris <-> T1

Only the 802.11 section is encrypted with IPsec, between the Soekris boxes,
everything else is unencrypted (unless the client Network/PC negotiaties
encryption on its own).  With a higher MTU on the 802.11 link, it can
handle IPsec encapsulation and still give the user a standard 1500 byte
mtu end-to-end.

Index: if_wi.c
===================================================================
RCS file: /cvs/src/sys/dev/ic/if_wi.c,v
retrieving revision 1.94
diff -u -r1.94 if_wi.c
--- if_wi.c     10 Mar 2003 00:59:54 -0000      1.94
+++ if_wi.c     22 Apr 2003 17:31:44 -0000
@@ -1541,10 +1541,15 @@
                break;
 
        case SIOCSIFMTU:
-               if (ifr->ifr_mtu > ETHERMTU || ifr->ifr_mtu < ETHERMIN) {
+               if (ifr->ifr_mtu > WI_DEFAULT_DATALEN || ifr->ifr_mtu <
+                   ETHERMIN) {
                        error = EINVAL;
                } else if (ifp->if_mtu != ifr->ifr_mtu) {
                        ifp->if_mtu = ifr->ifr_mtu;
+               }
+               if (ifr->ifr_mtu > sc->wi_max_data_len) {
+                       sc->wi_max_data_len = ifr->ifr_mtu;
+                       WI_SETVAL(WI_RID_MAX_DATALEN, sc->wi_max_data_len);
                }
                break;