Teach pppoe(4) about RFC 4638. This allows negotiating increased MTU with

compatible equipment provided that the physical interface and other layer 2
devices involved support and are configured to use jumbo frames.

Manpage to follow; typical use is to request 1500 MTU for pppoe, this
requires 1508+ MTU on the physical interface, e.g. "ifconfig em0 mtu 1508;
ifconfig pppoe0 mtu 1500". Known to be usable in the UK with some ISPs
(e.g. aaisp) using BT FTTC backhaul.

From Matt Dainty, originally based on support in NetBSD, changed to
decouple pppoe from physical interface MTU. Tested with UK FTTC by Matt,
no regressions on my standard UK ADSL setup or yasuoka@'s setup (in Japan,
NTT uses 1452 byte MTU for PPPoE and 1500 byte MTU for IPv6 on the same
network).

ok yasuoka@

1 files changed, 25 insertions, 14 deletions

diff --git a/sys/net/if_spppsubr.c b/sys/net/if_spppsubr.c
index 35cdad33106..210b4ceb62c 100644
--- a/sys/net/if_spppsubr.c
+++ b/sys/net/if_spppsubr.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: if_spppsubr.c,v 1.94 2011/07/07 00:08:04 henning Exp $	*/
+/*	$OpenBSD: if_spppsubr.c,v 1.95 2012/01/19 01:13:20 sthen Exp $	*/
 /*
  * Synchronous PPP/Cisco link level subroutines.
  * Keepalive protocol implemented in both Cisco and PPP modes.
@@ -1118,7 +1118,9 @@ sppp_ioctl(struct ifnet *ifp, u_long cmd, void *data)
 
 #ifdef SIOCSIFMTU
 	case SIOCSIFMTU:
-		if (ifr->ifr_mtu < 128 || ifr->ifr_mtu > sp->lcp.their_mru) {
+		if (ifr->ifr_mtu < 128 ||
+		    (sp->lcp.their_mru > 0 &&
+		     ifr->ifr_mtu > sp->lcp.their_mru)) {
 			splx(s);
 			return (EINVAL);
 		}
@@ -1127,7 +1129,9 @@ sppp_ioctl(struct ifnet *ifp, u_long cmd, void *data)
 #endif
 #ifdef SLIOCSETMTU
 	case SLIOCSETMTU:
-		if (*(short*)data < 128 || *(short*)data > sp->lcp.their_mru) {
+		if (*(short*)data < 128 ||
+		    (sp->lcp.their_mru > 0 &&
+		     *(short*)data > sp->lcp.their_mru)) {
 			splx(s);
 			return (EINVAL);
 		}
@@ -1710,7 +1714,7 @@ sppp_cp_input(const struct cp *cp, struct sppp *sp, struct mbuf *m)
 			/* Line loopback mode detected. */
 			log(LOG_INFO, SPP_FMT "loopback\n", SPP_ARGS(ifp));
 			/* Shut down the PPP link. */
- 			lcp.Close(sp);
+			lcp.Close(sp);
 			break;
 		}
 
@@ -2027,7 +2031,8 @@ sppp_lcp_init(struct sppp *sp)
 	sp->state[IDX_LCP] = STATE_INITIAL;
 	sp->fail_counter[IDX_LCP] = 0;
 	sp->lcp.protos = 0;
-	sp->lcp.mru = sp->lcp.their_mru = sp->pp_if.if_mtu;
+	sp->lcp.mru = sp->pp_if.if_mtu;
+	sp->lcp.their_mru = 0;
 
 	/*
 	 * Initialize counters and timeout values.  Note that we don't
@@ -2059,11 +2064,16 @@ sppp_lcp_up(struct sppp *sp)
 		return;
 	}
 
- 	sp->pp_alivecnt = 0;
- 	sp->lcp.opts = (1 << LCP_OPT_MAGIC);
- 	sp->lcp.magic = 0;
- 	sp->lcp.protos = 0;
- 	sp->lcp.mru = sp->lcp.their_mru = sp->pp_if.if_mtu;
+	sp->pp_alivecnt = 0;
+	sp->lcp.opts = (1 << LCP_OPT_MAGIC);
+	sp->lcp.magic = 0;
+	sp->lcp.protos = 0;
+	if (sp->pp_if.if_mtu != PP_MTU) {
+		sp->lcp.mru = sp->pp_if.if_mtu;
+		sp->lcp.opts |= (1 << LCP_OPT_MRU);
+	} else
+		sp->lcp.mru = PP_MTU;
+	sp->lcp.their_mru = PP_MTU;
 
 	getmicrouptime(&tv);
 	sp->pp_last_receive = sp->pp_last_activity = tv.tv_sec;
@@ -2129,9 +2139,10 @@ sppp_lcp_down(struct sppp *sp)
 
 	if (sp->state[IDX_LCP] != STATE_INITIAL)
 		lcp.Close(sp);
- 	sp->pp_flags &= ~PP_CALLIN;
+	sp->lcp.their_mru = 0;
+	sp->pp_flags &= ~PP_CALLIN;
 	ifp->if_flags &= ~IFF_RUNNING;
- 	sppp_flush(ifp);
+	sppp_flush(ifp);
 }
 
 HIDE void
@@ -4710,8 +4721,8 @@ sppp_set_ip_addrs(void *arg1, void *arg2)
 	u_int32_t hisaddr = args->hisaddr;
 	struct ifnet *ifp = &sp->pp_if;
 	int debug = ifp->if_flags & IFF_DEBUG;
- 	struct ifaddr *ifa;
- 	struct sockaddr_in *si;
+	struct ifaddr *ifa;
+	struct sockaddr_in *si;
 	struct sockaddr_in *dest;
 	int s;