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, 48 insertions, 8 deletions

diff --git a/sys/net/if_pppoe.c b/sys/net/if_pppoe.c
index a84c0682c7f..ff685077e71 100644
--- a/sys/net/if_pppoe.c
+++ b/sys/net/if_pppoe.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: if_pppoe.c,v 1.33 2011/07/06 02:42:28 henning Exp $ */
+/* $OpenBSD: if_pppoe.c,v 1.34 2012/01/19 01:13:20 sthen Exp $ */
 /* $NetBSD: if_pppoe.c,v 1.51 2003/11/28 08:56:48 keihan Exp $ */
 
 /*
@@ -86,9 +86,10 @@ struct pppoetag {
 #define	PPPOE_TAG_ACCOOKIE	0x0104		/* AC cookie */
 #define	PPPOE_TAG_VENDOR	0x0105		/* vendor specific */
 #define	PPPOE_TAG_RELAYSID	0x0110		/* relay session id */
+#define	PPPOE_TAG_MAX_PAYLOAD	0x0120		/* RFC 4638 max payload */
 #define	PPPOE_TAG_SNAME_ERR	0x0201		/* service name error */
 #define	PPPOE_TAG_ACSYS_ERR	0x0202		/* AC system error */
-#define	PPPOE_TAG_GENERIC_ERR	0x0203		/* gerneric error */
+#define	PPPOE_TAG_GENERIC_ERR	0x0203		/* generic error */
 
 #define	PPPOE_CODE_PADI		0x09		/* Active Discovery Initiation */
 #define	PPPOE_CODE_PADO		0x07		/* Active Discovery Offer */
@@ -97,7 +98,8 @@ struct pppoetag {
 #define	PPPOE_CODE_PADT		0xA7		/* Active Discovery Terminate */
 
 /* two byte PPP protocol discriminator, then IP data */
-#define	PPPOE_MAXMTU	(ETHERMTU - PPPOE_OVERHEAD)
+#define	PPPOE_MTU	(ETHERMTU - PPPOE_OVERHEAD)
+#define	PPPOE_MAXMTU	PP_MAX_MRU
 
 /* Add a 16 bit unsigned value to a buffer pointed to by PTR */
 #define	PPPOE_ADD_16(PTR, VAL)			\
@@ -225,7 +227,7 @@ pppoe_clone_create(struct if_clone *ifc, int unit)
 		 sizeof(sc->sc_sppp.pp_if.if_xname), 
 		 "pppoe%d", unit);
 	sc->sc_sppp.pp_if.if_softc = sc;
-	sc->sc_sppp.pp_if.if_mtu = PPPOE_MAXMTU;
+	sc->sc_sppp.pp_if.if_mtu = PPPOE_MTU;
 	sc->sc_sppp.pp_if.if_flags = IFF_SIMPLEX | IFF_POINTOPOINT | IFF_MULTICAST;
 	sc->sc_sppp.pp_if.if_type = IFT_PPP;
 	sc->sc_sppp.pp_if.if_hdrlen = sizeof(struct ether_header) + PPPOE_HEADERLEN;
@@ -398,6 +400,7 @@ static void pppoe_dispatch_disc_pkt(struct mbuf *m, int off)
 	size_t ac_cookie_len;
 	size_t relay_sid_len;
 	int noff, err, errortag;
+	u_int16_t *max_payload;
 	u_int16_t tag, len;
 	u_int16_t session, plen;
 	u_int8_t *ac_cookie;
@@ -424,6 +427,7 @@ static void pppoe_dispatch_disc_pkt(struct mbuf *m, int off)
 	ac_cookie_len = 0;
 	relay_sid = NULL;
 	relay_sid_len = 0;
+	max_payload = NULL;
 #ifdef PPPOE_SERVER
 	hunique = NULL;
 	hunique_len = 0;
@@ -531,6 +535,18 @@ static void pppoe_dispatch_disc_pkt(struct mbuf *m, int off)
 				relay_sid_len = len;
 			}
 			break;
+		case PPPOE_TAG_MAX_PAYLOAD:
+			if (max_payload == NULL) {
+				n = m_pulldown(m, off, len,
+				    &noff);
+				if (n == NULL || len != 2) {
+					err_msg = "TAG MAX_PAYLOAD ERROR";
+					m = NULL;
+					break;
+				}
+				max_payload = (u_int16_t *)(mtod(n, caddr_t) + noff);
+			}
+			break;
 		case PPPOE_TAG_SNAME_ERR:
 			err_msg = "SERVICE NAME ERROR";
 			errortag = 1;
@@ -679,6 +695,13 @@ breakbreak:
 			sc->sc_relay_sid_len = relay_sid_len;
 			memcpy(sc->sc_relay_sid, relay_sid, relay_sid_len);
 		}
+		if (sc->sc_sppp.pp_if.if_mtu > PPPOE_MTU &&
+		    (max_payload == NULL ||
+		     ntohs(*max_payload) != sc->sc_sppp.pp_if.if_mtu)) {
+			printf("%s: No valid PPP-Max-Payload tag received in PADO\n",
+			    sc->sc_sppp.pp_if.if_xname);
+			sc->sc_sppp.pp_if.if_mtu = PPPOE_MTU;
+		}
 		
 		memcpy(&sc->sc_dest, eh->ether_shost, sizeof(sc->sc_dest));
 		sc->sc_padr_retried = 0;
@@ -1008,8 +1031,9 @@ pppoe_ioctl(struct ifnet *ifp, unsigned long cmd, caddr_t data)
 	{
 		struct ifreq *ifr = (struct ifreq *)data;
 
-		if (ifr->ifr_mtu > (sc->sc_eth_if == NULL ?
-		    PPPOE_MAXMTU : (sc->sc_eth_if->if_mtu - PPPOE_OVERHEAD)))
+		if (ifr->ifr_mtu > MIN(PPPOE_MAXMTU,
+		    (sc->sc_eth_if == NULL ? PPPOE_MAXMTU :
+		    (sc->sc_eth_if->if_mtu - PPPOE_OVERHEAD))))
 			return (EINVAL);
 		return (sppp_ioctl(ifp, cmd, data));
 	}
@@ -1068,6 +1092,8 @@ pppoe_send_padi(struct pppoe_softc *sc)
 		l2 = strlen(sc->sc_concentrator_name);
 		len += 2 + 2 + l2;
 	}
+	if (sc->sc_sppp.pp_if.if_mtu > PPPOE_MTU)
+		len += 2 + 2 + 2;
 
 	/* allocate a buffer */
 	m0 = pppoe_get_mbuf(len + PPPOE_HEADERLEN);	/* header len + payload len */
@@ -1094,9 +1120,15 @@ pppoe_send_padi(struct pppoe_softc *sc)
 	PPPOE_ADD_16(p, PPPOE_TAG_HUNIQUE);
 	PPPOE_ADD_16(p, sizeof(sc->sc_unique));
 	memcpy(p, &sc->sc_unique, sizeof(sc->sc_unique));
+	p += sizeof(sc->sc_unique);
+
+	if (sc->sc_sppp.pp_if.if_mtu > PPPOE_MTU) {
+		PPPOE_ADD_16(p, PPPOE_TAG_MAX_PAYLOAD);
+		PPPOE_ADD_16(p, 2);
+		PPPOE_ADD_16(p, (u_int16_t)sc->sc_sppp.pp_if.if_mtu);
+	}
 
 #ifdef PPPOE_DEBUG
-	p += sizeof(sc->sc_unique);
 	if (p - mtod(m0, u_int8_t *) != len + PPPOE_HEADERLEN)
 		panic("pppoe_send_padi: garbled output len, should be %ld, is %ld",
 		    (long)(len + PPPOE_HEADERLEN), (long)(p - mtod(m0, u_int8_t *)));
@@ -1298,6 +1330,8 @@ pppoe_send_padr(struct pppoe_softc *sc)
 		len += 2 + 2 + sc->sc_ac_cookie_len;	/* AC cookie */
 	if (sc->sc_relay_sid_len > 0)
 		len += 2 + 2 + sc->sc_relay_sid_len;	/* Relay SID */
+	if (sc->sc_sppp.pp_if.if_mtu > PPPOE_MTU)
+		len += 2 + 2 + 2;
 
 	m0 = pppoe_get_mbuf(len + PPPOE_HEADERLEN);
 	if (m0 == NULL)
@@ -1329,9 +1363,15 @@ pppoe_send_padr(struct pppoe_softc *sc)
 	PPPOE_ADD_16(p, PPPOE_TAG_HUNIQUE);
 	PPPOE_ADD_16(p, sizeof(sc->sc_unique));
 	memcpy(p, &sc->sc_unique, sizeof(sc->sc_unique));
+	p += sizeof(sc->sc_unique);
+
+	if (sc->sc_sppp.pp_if.if_mtu > PPPOE_MTU) {
+		PPPOE_ADD_16(p, PPPOE_TAG_MAX_PAYLOAD);
+		PPPOE_ADD_16(p, 2);
+		PPPOE_ADD_16(p, (u_int16_t)sc->sc_sppp.pp_if.if_mtu);
+	}
 
 #ifdef PPPOE_DEBUG
-	p += sizeof(sc->sc_unique);
 	if (p - mtod(m0, u_int8_t *) != len + PPPOE_HEADERLEN)
 		panic("pppoe_send_padr: garbled output len, should be %ld, is %ld",
 			(long)(len + PPPOE_HEADERLEN), (long)(p - mtod(m0, u_int8_t *)));