Handle hardware-imposed MTU/MRU limitations. PPPoE will no longer

allow MRU/MTU negotiations to exceed 1492.

Add an optional ``max'' specifier to ``set m[rt]u'', ie.

	set mtu max 1480

Bump the ppp version number.

Sponsored by:	Monzoon Networks AG and FreeBSD Services Limited

21 files changed, 246 insertions, 80 deletions

diff --git a/usr.sbin/ppp/atm.c b/usr.sbin/ppp/atm.c
index 30ce98a..6d6aba9 100644
--- a/usr.sbin/ppp/atm.c
+++ b/usr.sbin/ppp/atm.c
@@ -122,6 +122,7 @@ atm_device2iov(struct device *d, struct iovec *iov, int *niov,
 static const struct device baseatmdevice = {
   ATM_DEVICE,
   "atm",
+  0,
   { CD_NOTREQUIRED, 0 },
   NULL,
   NULL,
diff --git a/usr.sbin/ppp/bundle.c b/usr.sbin/ppp/bundle.c
index f8d8ad6..7e48499 100644
--- a/usr.sbin/ppp/bundle.c
+++ b/usr.sbin/ppp/bundle.c
@@ -802,7 +802,6 @@ bundle_Create(const char *prefix, int type, int unit)
   log_Printf(LogPHASE, "Using interface: %s\n", ifname);
 
   bundle.bandwidth = 0;
-  bundle.mtu = 1500;
   bundle.routing_seq = 0;
   bundle.phase = PHASE_DEAD;
   bundle.CleaningUp = 0;
@@ -821,7 +820,6 @@ bundle_Create(const char *prefix, int type, int unit)
   bundle.cfg.opt = OPT_SROUTES | OPT_IDCHECK | OPT_LOOPBACK | OPT_TCPMSSFIXUP |
                    OPT_THROUGHPUT | OPT_UTMP;
   *bundle.cfg.label = '\0';
-  bundle.cfg.mtu = DEF_MTU;
   bundle.cfg.ifqueue = DEF_IFQUEUE;
   bundle.cfg.choked.timeout = CHOKED_TIMEOUT;
   bundle.phys_type.all = type;
@@ -1096,11 +1094,6 @@ bundle_ShowStatus(struct cmdargs const *arg)
     prompt_Printf(arg->prompt, "\n");
   } else
     prompt_Printf(arg->prompt, "disabled\n");
-  prompt_Printf(arg->prompt, " MTU:               ");
-  if (arg->bundle->cfg.mtu)
-    prompt_Printf(arg->prompt, "%d\n", arg->bundle->cfg.mtu);
-  else
-    prompt_Printf(arg->prompt, "unspecified\n");
 
   prompt_Printf(arg->prompt, " sendpipe:          ");
   if (arg->bundle->ncp.ipcp.cfg.sendpipe > 0)
@@ -1826,7 +1819,7 @@ bundle_CalculateBandwidth(struct bundle *bundle)
   int sp;
 
   bundle->bandwidth = 0;
-  bundle->mtu = 0;
+  bundle->iface->mtu = 0;
   for (dl = bundle->links; dl; dl = dl->next)
     if (dl->state == DATALINK_OPEN) {
       if ((sp = dl->mp.bandwidth) == 0 &&
@@ -1836,7 +1829,7 @@ bundle_CalculateBandwidth(struct bundle *bundle)
       else
         bundle->bandwidth += sp;
       if (!bundle->ncp.mp.active) {
-        bundle->mtu = dl->physical->link.lcp.his_mru;
+        bundle->iface->mtu = dl->physical->link.lcp.his_mru;
         break;
       }
     }
@@ -1845,16 +1838,16 @@ bundle_CalculateBandwidth(struct bundle *bundle)
     bundle->bandwidth = 115200;		/* Shrug */
 
   if (bundle->ncp.mp.active)
-    bundle->mtu = bundle->ncp.mp.peer_mrru;
-  else if (!bundle->mtu)
-    bundle->mtu = 1500;
+    bundle->iface->mtu = bundle->ncp.mp.peer_mrru;
+  else if (!bundle->iface->mtu)
+    bundle->iface->mtu = DEF_MRU;
 
 #ifndef NORADIUS
   if (bundle->radius.valid && bundle->radius.mtu &&
-      bundle->radius.mtu < bundle->mtu) {
+      bundle->radius.mtu < bundle->iface->mtu) {
     log_Printf(LogLCP, "Reducing MTU to radius value %lu\n",
                bundle->radius.mtu);
-    bundle->mtu = bundle->radius.mtu;
+    bundle->iface->mtu = bundle->radius.mtu;
   }
 #endif
 
diff --git a/usr.sbin/ppp/bundle.h b/usr.sbin/ppp/bundle.h
index 2953631..de8cb13 100644
--- a/usr.sbin/ppp/bundle.h
+++ b/usr.sbin/ppp/bundle.h
@@ -73,7 +73,6 @@ struct bundle {
   } dev;
 
   u_long bandwidth;           /* struct tuninfo speed */
-  int mtu;                    /* struct tuninfo MTU */
   struct iface *iface;        /* Interface information */
 
   int routing_seq;            /* The current routing sequence number */
@@ -103,7 +102,6 @@ struct bundle {
     } auth;
     unsigned opt;             /* Uses OPT_ bits from above */
     char label[50];           /* last thing `load'ed */
-    u_short mtu;              /* Required interface MTU */
     u_short ifqueue;          /* Interface queue size */
 
     struct {
diff --git a/usr.sbin/ppp/command.c b/usr.sbin/ppp/command.c
index 4f205f5..62415b1 100644
--- a/usr.sbin/ppp/command.c
+++ b/usr.sbin/ppp/command.c
@@ -159,7 +159,7 @@
 #define NEG_MPPE	54
 #define NEG_CHAP81	55
 
-const char Version[] = "2.3.1";
+const char Version[] = "2.3.2";
 
 static int ShowCommand(struct cmdargs const *);
 static int TerminalCommand(struct cmdargs const *);
@@ -1489,6 +1489,7 @@ SetVariable(struct cmdargs const *arg)
 {
   long long_val, param = (long)arg->cmd->args;
   int mode, dummyint, f, first;
+  u_short *change;
   const char *argp;
   struct datalink *cx = arg->cx;	/* LOCAL_CX uses this */
   const char *err = NULL;
@@ -1678,9 +1679,36 @@ SetVariable(struct cmdargs const *arg)
     break;
 
   case VAR_MRU:
-    long_val = atol(argp);
+    switch(arg->argc - arg->argn) {
+    case 1:
+      if (argp[strspn(argp, "0123456789")] != '\0')
+        return -1;
+    case 0:
+      long_val = atol(argp);
+      change = &l->lcp.cfg.mru;
+      if (long_val > l->lcp.cfg.max_mru) {
+        log_Printf(LogWARN, "MRU %ld: too large - max set to %d\n", long_val,
+                   l->lcp.cfg.max_mru);
+        return 1;
+      }
+      break;
+    case 2:
+      if (strcasecmp(argp, "max") && strcasecmp(argp, "maximum"))
+        return -1;
+      long_val = atol(arg->argv[arg->argn + 1]);
+      change = &l->lcp.cfg.max_mru;
+      if (long_val > MAX_MRU) {
+        log_Printf(LogWARN, "MRU %ld: too large - maximum is %d\n", long_val,
+                   MAX_MRU);
+        return 1;
+      }
+      break;
+    default:
+      return -1;
+    }
+
     if (long_val == 0)
-      l->lcp.cfg.mru = DEF_MRU;
+      *change = DEF_MRU;
     else if (long_val < MIN_MRU) {
       log_Printf(LogWARN, "MRU %ld: too small - min %d\n", long_val, MIN_MRU);
       return 1;
@@ -1688,11 +1716,40 @@ SetVariable(struct cmdargs const *arg)
       log_Printf(LogWARN, "MRU %ld: too big - max %d\n", long_val, MAX_MRU);
       return 1;
     } else
-      l->lcp.cfg.mru = long_val;
+      *change = long_val;
+    if (l->lcp.cfg.mru > *change)
+      l->lcp.cfg.mru = *change;
     break;
 
   case VAR_MTU:
-    long_val = atol(argp);
+    switch(arg->argc - arg->argn) {
+    case 1:
+      if (argp[strspn(argp, "0123456789")] != '\0')
+        return -1;
+    case 0:
+      long_val = atol(argp);
+      change = &l->lcp.cfg.mtu;
+      if (long_val > l->lcp.cfg.max_mtu) {
+        log_Printf(LogWARN, "MTU %ld: too large - max set to %d\n", long_val,
+                   l->lcp.cfg.max_mtu);
+        return 1;
+      }
+      break;
+    case 2:
+      if (strcasecmp(argp, "max") && strcasecmp(argp, "maximum"))
+        return -1;
+      long_val = atol(arg->argv[arg->argn + 1]);
+      change = &l->lcp.cfg.max_mtu;
+      if (long_val > MAX_MTU) {
+        log_Printf(LogWARN, "MTU %ld: too large - maximum is %d\n", long_val,
+                   MAX_MTU);
+        return 1;
+      }
+      break;
+    default:
+      return -1;
+    }
+
     if (long_val && long_val < MIN_MTU) {
       log_Printf(LogWARN, "MTU %ld: too small - min %d\n", long_val, MIN_MTU);
       return 1;
@@ -1700,7 +1757,9 @@ SetVariable(struct cmdargs const *arg)
       log_Printf(LogWARN, "MTU %ld: too big - max %d\n", long_val, MAX_MTU);
       return 1;
     } else
-      arg->bundle->cfg.mtu = long_val;
+      *change = long_val;
+    if (l->lcp.cfg.mtu > *change)
+      l->lcp.cfg.mtu = *change;
     break;
 
   case VAR_OPENMODE:
@@ -2064,9 +2123,9 @@ static struct cmdtab const SetCommands[] = {
   {"mrru", NULL, SetVariable, LOCAL_AUTH, "MRRU value",
   "set mrru value", (const void *)VAR_MRRU},
   {"mru", NULL, SetVariable, LOCAL_AUTH | LOCAL_CX_OPT,
-  "MRU value", "set mru value", (const void *)VAR_MRU},
-  {"mtu", NULL, SetVariable, LOCAL_AUTH,
-  "interface MTU value", "set mtu value", (const void *)VAR_MTU},
+  "MRU value", "set mru [max[imum]] [value]", (const void *)VAR_MRU},
+  {"mtu", NULL, SetVariable, LOCAL_AUTH | LOCAL_CX,
+  "interface MTU value", "set mtu [max[imum]] [value]", (const void *)VAR_MTU},
   {"nbns", NULL, SetVariable, LOCAL_AUTH, "NetBIOS Name Server",
   "set nbns pri-addr [sec-addr]", (const void *)VAR_NBNS},
   {"openmode", NULL, SetVariable, LOCAL_AUTH | LOCAL_CX, "open mode",
diff --git a/usr.sbin/ppp/ether.c b/usr.sbin/ppp/ether.c
index 0af8ff5..1e8d53c 100644
--- a/usr.sbin/ppp/ether.c
+++ b/usr.sbin/ppp/ether.c
@@ -285,6 +285,7 @@ ether_AwaitCarrier(struct physical *p)
 static const struct device baseetherdevice = {
   ETHER_DEVICE,
   "ether",
+  1492,
   { CD_REQUIRED, DEF_ETHERCDDELAY },
   ether_AwaitCarrier,
   ether_RemoveFromSet,
@@ -675,16 +676,6 @@ ether_Create(struct physical *p)
   if (dev) {
     physical_SetupStack(p, dev->dev.name, PHYSICAL_FORCE_SYNCNOACF);
 
-    /* Moan about (and fix) invalid LCP configurations */
-    if (p->link.lcp.cfg.mru > 1492) {
-      log_Printf(LogWARN, "%s: Reducing MRU to 1492\n", p->link.name);
-      p->link.lcp.cfg.mru = 1492;
-    }
-    if (p->dl->bundle->cfg.mtu > 1492) {
-      log_Printf(LogWARN, "%s: Reducing MTU to 1492\n", p->link.name);
-      p->dl->bundle->cfg.mtu = 1492;
-    }
-
     if (path != NULL) {
       /* Mark the interface as UP if it's not already */
 
diff --git a/usr.sbin/ppp/exec.c b/usr.sbin/ppp/exec.c
index 1ca9665..2522653 100644
--- a/usr.sbin/ppp/exec.c
+++ b/usr.sbin/ppp/exec.c
@@ -68,6 +68,7 @@
 static struct device execdevice = {
   EXEC_DEVICE,
   "exec",
+  0,
   { CD_NOTREQUIRED, 0 },
   NULL,
   NULL,
diff --git a/usr.sbin/ppp/i4b.c b/usr.sbin/ppp/i4b.c
index fe82fae..855bfce 100644
--- a/usr.sbin/ppp/i4b.c
+++ b/usr.sbin/ppp/i4b.c
@@ -293,6 +293,7 @@ i4b_device2iov(struct device *d, struct iovec *iov, int *niov,
 static struct device basei4bdevice = {
   I4B_DEVICE,
   "i4b",
+  0,
   { CD_REQUIRED, DEF_I4BCDDELAY },
   i4b_AwaitCarrier,
   NULL,
diff --git a/usr.sbin/ppp/iface.c b/usr.sbin/ppp/iface.c
index 5384340..9676b38 100644
--- a/usr.sbin/ppp/iface.c
+++ b/usr.sbin/ppp/iface.c
@@ -163,8 +163,9 @@ iface_Create(const char *name)
         return NULL;
       }
       iface->name = strdup(name);
-      iface->flags = ifm->ifm_flags;
       iface->index = ifm->ifm_index;
+      iface->flags = ifm->ifm_flags;
+      iface->mtu = 0;
       iface->in_addrs = 0;
       iface->in_addr = NULL;
     }
@@ -540,7 +541,7 @@ iface_Show(struct cmdargs const *arg)
                     if_flags[f].value);
       flags &= ~if_flags[f].flag;
     }
-  prompt_Printf(arg->prompt, "> mtu %d has %d address%s:\n", arg->bundle->mtu,
+  prompt_Printf(arg->prompt, "> mtu %d has %d address%s:\n", iface->mtu,
                 iface->in_addrs, iface->in_addrs == 1 ? "" : "es");
 
   for (f = 0; f < iface->in_addrs; f++) {
diff --git a/usr.sbin/ppp/iface.h b/usr.sbin/ppp/iface.h
index 6de1b50..d520e84 100644
--- a/usr.sbin/ppp/iface.h
+++ b/usr.sbin/ppp/iface.h
@@ -39,6 +39,7 @@ struct iface {
   char *name;			/* Interface name (malloc'd) */
   int index;			/* Interface index */
   int flags;			/* Interface flags (IFF_*) */
+  int mtu;			/* struct tuninfo MTU */
 
   int in_addrs;			/* How many in_addr's */
   struct iface_addr *in_addr;	/* Array of addresses (malloc'd) */
diff --git a/usr.sbin/ppp/lcp.c b/usr.sbin/ppp/lcp.c
index f4bfee4..25c893b 100644
--- a/usr.sbin/ppp/lcp.c
+++ b/usr.sbin/ppp/lcp.c
@@ -177,7 +177,13 @@ lcp_ReportStatus(struct cmdargs const *arg)
                 (u_long)lcp->want_magic, lcp->want_mrru,
                 lcp->want_shortseq ? "on" : "off", lcp->my_reject);
 
-  prompt_Printf(arg->prompt, "\n Defaults: MRU = %d, ", lcp->cfg.mru);
+  prompt_Printf(arg->prompt, "\n Defaults: MRU = %d (max %d), ",
+                lcp->cfg.mru, lcp->cfg.max_mru);
+  if (lcp->cfg.mtu)
+    prompt_Printf(arg->prompt, "MTU = %d (max %d), ",
+                  lcp->cfg.mtu, lcp->cfg.max_mtu);
+  else
+    prompt_Printf(arg->prompt, "MTU = any (max %d), ", lcp->cfg.max_mtu);
   prompt_Printf(arg->prompt, "ACCMAP = %08lx\n", (u_long)lcp->cfg.accmap);
   prompt_Printf(arg->prompt, "           LQR period = %us, ",
                 lcp->cfg.lqrperiod);
@@ -241,6 +247,9 @@ lcp_Init(struct lcp *lcp, struct bundle *bundle, struct link *l,
            bundle, l, parent, &lcp_Callbacks, lcp_TimerNames);
 
   lcp->cfg.mru = DEF_MRU;
+  lcp->cfg.max_mru = MAX_MRU;
+  lcp->cfg.mtu = 0;
+  lcp->cfg.max_mtu = MAX_MTU;
   lcp->cfg.accmap = 0;
   lcp->cfg.openmode = 1;
   lcp->cfg.lqrperiod = DEF_LQRPERIOD;
@@ -266,11 +275,12 @@ lcp_Init(struct lcp *lcp, struct bundle *bundle, struct link *l,
 void
 lcp_Setup(struct lcp *lcp, int openmode)
 {
+  struct physical *p = link2physical(lcp->fsm.link);
+  int phmtu = p ? physical_DeviceMTU(p) : 0;
+
   lcp->fsm.open_mode = openmode;
 
-  lcp->his_mru = lcp->fsm.bundle->cfg.mtu;
-  if (!lcp->his_mru || lcp->his_mru > DEF_MRU)
-    lcp->his_mru = DEF_MRU;
+  lcp->his_mru = DEF_MRU;
   lcp->his_mrru = 0;
   lcp->his_magic = 0;
   lcp->his_lqrperiod = 0;
@@ -281,13 +291,13 @@ lcp_Setup(struct lcp *lcp, int openmode)
   lcp->his_shortseq = 0;
 
   lcp->want_mru = lcp->cfg.mru;
+  if (phmtu && lcp->want_mru > phmtu)
+    lcp->want_mru = phmtu;
   lcp->want_mrru = lcp->fsm.bundle->ncp.mp.cfg.mrru;
   lcp->want_shortseq = IsEnabled(lcp->fsm.bundle->ncp.mp.cfg.shortseq) ? 1 : 0;
   lcp->want_acfcomp = IsEnabled(lcp->cfg.acfcomp) ? 1 : 0;
 
   if (lcp->fsm.parent) {
-    struct physical *p = link2physical(lcp->fsm.link);
-
     lcp->his_accmap = 0xffffffff;
     lcp->want_accmap = lcp->cfg.accmap;
     lcp->his_protocomp = 0;
@@ -592,15 +602,15 @@ LcpDecodeConfig(struct fsm *fp, u_char *cp, int plen, int mode_type,
 {
   /* Deal with incoming PROTO_LCP */
   struct lcp *lcp = fsm2lcp(fp);
-  int type, length, sz, pos, op, callback_req;
+  int type, length, sz, pos, op, callback_req, mru_req;
   u_int32_t magic, accmap;
-  u_short mtu, mru, proto;
+  u_short mru, phmtu, proto;
   struct lqrreq *req;
   char request[20], desc[22];
   struct mp *mp;
   struct physical *p = link2physical(fp->link);
 
-  sz = op = callback_req = 0;
+  sz = op = callback_req = mru_req = 0;
 
   while (plen >= sizeof(struct fsmconfig)) {
     type = *cp;
@@ -626,7 +636,13 @@ LcpDecodeConfig(struct fsm *fp, u_char *cp, int plen, int mode_type,
             /* Ignore his previous reject so that we REQ next time */
 	    lcp->his_reject &= ~(1 << type);
 
-          if (mru < MIN_MRU) {
+          if (mru > MAX_MRU) {
+            /* Push him down to MAX_MRU */
+            lcp->his_mrru = MAX_MRU;
+	    memcpy(dec->nakend, cp, 2);
+            ua_htons(&lcp->his_mrru, dec->nakend + 2);
+	    dec->nakend += 4;
+          } else if (mru < MIN_MRU) {
             /* Push him up to MIN_MRU */
             lcp->his_mrru = MIN_MRU;
 	    memcpy(dec->nakend, cp, 2);
@@ -664,28 +680,41 @@ LcpDecodeConfig(struct fsm *fp, u_char *cp, int plen, int mode_type,
       break;
 
     case TY_MRU:
+      mru_req = 1;
       ua_ntohs(cp + 2, &mru);
       log_Printf(LogLCP, "%s %d\n", request, mru);
 
       switch (mode_type) {
       case MODE_REQ:
-        mtu = lcp->fsm.bundle->cfg.mtu;
-        if (mru < MIN_MRU || (!lcp->want_mrru && mru < mtu)) {
+        phmtu = p ? physical_DeviceMTU(p) : 0;
+        if (phmtu && mru > phmtu) {
+          lcp->his_mru = lcp->cfg.mtu ? lcp->cfg.mtu : phmtu;
+          memcpy(dec->nakend, cp, 2);
+          ua_htons(&lcp->his_mru, dec->nakend + 2);
+          dec->nakend += 4;
+        } if (mru > lcp->cfg.max_mtu) {
+          lcp->his_mru = lcp->cfg.mtu ? lcp->cfg.mtu : lcp->cfg.max_mtu;
+          memcpy(dec->nakend, cp, 2);
+          ua_htons(&lcp->his_mru, dec->nakend + 2);
+          dec->nakend += 4;
+        } else if (mru < MIN_MRU || mru < lcp->cfg.mtu) {
           /* Push him up to MTU or MIN_MRU */
-          lcp->his_mru = mru < mtu ? mtu : MIN_MRU;
+          lcp->his_mru = mru < lcp->cfg.mtu ? lcp->cfg.mtu : MIN_MRU;
           memcpy(dec->nakend, cp, 2);
           ua_htons(&lcp->his_mru, dec->nakend + 2);
           dec->nakend += 4;
         } else {
-          lcp->his_mru = mtu ? mtu : mru;
+          lcp->his_mru = lcp->cfg.mtu ? lcp->cfg.mtu : mru;
           memcpy(dec->ackend, cp, 4);
           dec->ackend += 4;
         }
 	break;
       case MODE_NAK:
-        if (mru > MAX_MRU)
-          lcp->want_mru = MAX_MRU;
-        else if (mru < MIN_MRU)
+        if (mru > lcp->cfg.max_mru) {
+          lcp->want_mru = lcp->cfg.max_mru;
+          if (p && lcp->want_mru > physical_DeviceMTU(p))
+            lcp->want_mru = physical_DeviceMTU(p);
+        } else if (mru < MIN_MRU)
           lcp->want_mru = MIN_MRU;
         else
           lcp->want_mru = mru;
@@ -1217,6 +1246,22 @@ reqreject:
         dec->nakend[-1] = 2;	/* XXX: Silly ! */
       }
     }
+    if (mode_type == MODE_REQ && !mru_req) {
+      mru = DEF_MRU;
+      phmtu = p ? physical_DeviceMTU(p) : 0;
+      if (phmtu && mru > phmtu)
+        mru = phmtu;
+      if (mru > lcp->cfg.max_mtu)
+        mru = lcp->cfg.max_mtu;
+      if (mru < DEF_MRU) {
+        /* Don't let the peer use the default MRU */
+        lcp->his_mru = lcp->cfg.mtu && lcp->cfg.mtu < mru ? lcp->cfg.mtu : mru;
+        *dec->nakend++ = TY_MRU;
+        *dec->nakend++ = 4;
+        ua_htons(&lcp->his_mru, dec->nakend);
+        dec->nakend += 2;
+      }
+    }
     if (dec->rejend != dec->rej) {
       /* rejects are preferred */
       dec->ackend = dec->ack;
diff --git a/usr.sbin/ppp/lcp.h b/usr.sbin/ppp/lcp.h
index e86e3be..3e0e8b2 100644
--- a/usr.sbin/ppp/lcp.h
+++ b/usr.sbin/ppp/lcp.h
@@ -82,6 +82,9 @@ struct lcp {
 
   struct {
     u_short mru;		/* Preferred MRU value */
+    u_short max_mru;		/* Preferred MRU value */
+    u_short mtu;		/* Preferred MTU */
+    u_short max_mtu;		/* Preferred MTU */
     u_int32_t accmap;		/* Initial ACCMAP value */
     int openmode;		/* when to start CFG REQs */
     u_int32_t lqrperiod;	/* LQR frequency (seconds) */
diff --git a/usr.sbin/ppp/physical.c b/usr.sbin/ppp/physical.c
index e426890..76937e7 100644
--- a/usr.sbin/ppp/physical.c
+++ b/usr.sbin/ppp/physical.c
@@ -758,6 +758,12 @@ physical_IsSync(struct physical *p)
    return p->cfg.speed == 0;
 }
 
+u_short
+physical_DeviceMTU(struct physical *p)
+{
+  return p->handler ? p->handler->mtu : 0;
+}
+
 const char *physical_GetDevice(struct physical *p)
 {
    return p->name.full;
diff --git a/usr.sbin/ppp/physical.h b/usr.sbin/ppp/physical.h
index 90b8e7f..988b730 100644
--- a/usr.sbin/ppp/physical.h
+++ b/usr.sbin/ppp/physical.h
@@ -56,6 +56,7 @@ struct cd {
 struct device {
   int type;
   const char *name;
+  u_short mtu;
   struct cd cd;
 
   int (*awaitcarrier)(struct physical *);
@@ -143,6 +144,7 @@ extern const char *physical_LockedDevice(struct physical *);
 extern void physical_ChangedPid(struct physical *, pid_t);
 
 extern int physical_IsSync(struct physical *);
+extern u_short physical_DeviceMTU(struct physical *);
 extern const char *physical_GetDevice(struct physical *);
 extern void physical_SetDeviceList(struct physical *, int, const char *const *);
 extern void physical_SetDevice(struct physical *, const char *);
diff --git a/usr.sbin/ppp/ppp.8 b/usr.sbin/ppp/ppp.8
index acfd8fc..42743be 100644
--- a/usr.sbin/ppp/ppp.8
+++ b/usr.sbin/ppp/ppp.8
@@ -4917,32 +4917,60 @@ Setting this option enables Multi-link PPP negotiations, also known as
 Multi-link Protocol or MP.
 There is no default MRRU (Maximum Reconstructed Receive Unit) value.
 If no argument is given, multi-link mode is disabled.
-.It set mru Op Ar value
+.It set mru Oo max Ns Oo imum Oc Oc Op Ar value
 The default MRU (Maximum Receive Unit) is 1500.
 If it is increased, the other side *may* increase its MTU.
-There is no point in decreasing the MRU to below the default as the
+In theory there is no point in decreasing the MRU to below the default as the
 .Em PPP
-protocol *must* be able to accept packets of at least 1500 octets.
+protocol says implementations *must* be able to accept packets of at
+least 1500 octets.
+.Pp
+If the
+.Dq maximum
+keyword is used,
+.Nm
+will refuse to negotiate a higher value.
+The maximum MRU can be set to 2048 at most.
+Setting a maximum of less than 1500 violates the
+.Em PPP
+rfc, but may sometimes be necessary.
+For example,
+.Em PPPoE
+imposes a maximum of 1492 due to hardware limitations.
+.Pp
 If no argument is given, 1500 is assumed.
-.It set mtu Op Ar value
+A value must be given when
+.Dq maximum
+is specified.
+.It set mtu Oo max Ns Oo imum Oc Oc Op Ar value
 The default MTU is 1500.
 At negotiation time,
 .Nm
-will accept whatever MRU or MRRU that the peer wants (assuming it's
-not less than 296 bytes).
+will accept whatever MRU the peer requests (assuming it's
+not less than 296 bytes or greater than the assigned maximum).
 If the MTU is set,
 .Nm
-will not accept MRU/MRRU values less than
+will not accept MRU values less than
 .Ar value .
-When negotiations are complete, the MTU is assigned to the interface, even
-if the peer requested a higher value MRU/MRRU.
+When negotiations are complete, the MTU is used when writing to the
+interface, even if the peer requested a higher value MRU.
 This can be useful for
 limiting your packet size (giving better bandwidth sharing at the expense
 of more header data).
 .Pp
+If the
+.Dq maximum
+keyword is used,
+.Nm
+will refuse to negotiate a higher value.
+The maximum MTU can be set to 2048 at most.
+.Pp
 If no
 .Ar value
 is given, 1500, or whatever the peer asks for is used.
+A value must be given when
+.Dq maximum
+is specified.
 .It set nbns Op Ar x.x.x.x Op Ar y.y.y.y
 This option allows the setting of the Microsoft NetBIOS name server
 values to be returned at the peers request.
diff --git a/usr.sbin/ppp/ppp.8.m4 b/usr.sbin/ppp/ppp.8.m4
index acfd8fc..42743be 100644
--- a/usr.sbin/ppp/ppp.8.m4
+++ b/usr.sbin/ppp/ppp.8.m4
@@ -4917,32 +4917,60 @@ Setting this option enables Multi-link PPP negotiations, also known as
 Multi-link Protocol or MP.
 There is no default MRRU (Maximum Reconstructed Receive Unit) value.
 If no argument is given, multi-link mode is disabled.
-.It set mru Op Ar value
+.It set mru Oo max Ns Oo imum Oc Oc Op Ar value
 The default MRU (Maximum Receive Unit) is 1500.
 If it is increased, the other side *may* increase its MTU.
-There is no point in decreasing the MRU to below the default as the
+In theory there is no point in decreasing the MRU to below the default as the
 .Em PPP
-protocol *must* be able to accept packets of at least 1500 octets.
+protocol says implementations *must* be able to accept packets of at
+least 1500 octets.
+.Pp
+If the
+.Dq maximum
+keyword is used,
+.Nm
+will refuse to negotiate a higher value.
+The maximum MRU can be set to 2048 at most.
+Setting a maximum of less than 1500 violates the
+.Em PPP
+rfc, but may sometimes be necessary.
+For example,
+.Em PPPoE
+imposes a maximum of 1492 due to hardware limitations.
+.Pp
 If no argument is given, 1500 is assumed.
-.It set mtu Op Ar value
+A value must be given when
+.Dq maximum
+is specified.
+.It set mtu Oo max Ns Oo imum Oc Oc Op Ar value
 The default MTU is 1500.
 At negotiation time,
 .Nm
-will accept whatever MRU or MRRU that the peer wants (assuming it's
-not less than 296 bytes).
+will accept whatever MRU the peer requests (assuming it's
+not less than 296 bytes or greater than the assigned maximum).
 If the MTU is set,
 .Nm
-will not accept MRU/MRRU values less than
+will not accept MRU values less than
 .Ar value .
-When negotiations are complete, the MTU is assigned to the interface, even
-if the peer requested a higher value MRU/MRRU.
+When negotiations are complete, the MTU is used when writing to the
+interface, even if the peer requested a higher value MRU.
 This can be useful for
 limiting your packet size (giving better bandwidth sharing at the expense
 of more header data).
 .Pp
+If the
+.Dq maximum
+keyword is used,
+.Nm
+will refuse to negotiate a higher value.
+The maximum MTU can be set to 2048 at most.
+.Pp
 If no
 .Ar value
 is given, 1500, or whatever the peer asks for is used.
+A value must be given when
+.Dq maximum
+is specified.
 .It set nbns Op Ar x.x.x.x Op Ar y.y.y.y
 This option allows the setting of the Microsoft NetBIOS name server
 values to be returned at the peers request.
diff --git a/usr.sbin/ppp/route.c b/usr.sbin/ppp/route.c
index 2b63253..54f585a 100644
--- a/usr.sbin/ppp/route.c
+++ b/usr.sbin/ppp/route.c
@@ -577,9 +577,8 @@ route_UpdateMTU(struct bundle *bundle)
       log_Printf(LogTCPIP, "route_UpdateMTU: Netif: %d (%s), dst %s, mtu %d\n",
                  rtm->rtm_index, Index2Nam(rtm->rtm_index),
                  inet_ntoa(((struct sockaddr_in *)sa[RTAX_DST])->sin_addr),
-                 bundle->mtu);
-      rt_Update(bundle, in[RTAX_DST]->sin_addr,
-                         in[RTAX_GATEWAY]->sin_addr);
+                 bundle->iface->mtu);
+      rt_Update(bundle, in[RTAX_DST]->sin_addr, in[RTAX_GATEWAY]->sin_addr);
     }
   }
 
@@ -890,7 +889,7 @@ rt_Update(struct bundle *bundle, struct in_addr dst, struct in_addr gw)
     rtmes.m_rtm.rtm_inits |= RTV_RPIPE;
   }
 
-  rtmes.m_rtm.rtm_rmx.rmx_mtu = bundle->mtu;
+  rtmes.m_rtm.rtm_rmx.rmx_mtu = bundle->iface->mtu;
   rtmes.m_rtm.rtm_inits |= RTV_MTU;
 
   memset(&rtdata, '\0', sizeof rtdata);
diff --git a/usr.sbin/ppp/tcp.c b/usr.sbin/ppp/tcp.c
index b7482d1..567072a 100644
--- a/usr.sbin/ppp/tcp.c
+++ b/usr.sbin/ppp/tcp.c
@@ -100,6 +100,7 @@ tcp_OpenConnection(const char *name, char *host, char *port)
 static struct device tcpdevice = {
   TCP_DEVICE,
   "tcp",
+  0,
   { CD_NOTREQUIRED, 0 },
   NULL,
   NULL,
diff --git a/usr.sbin/ppp/tcpmss.c b/usr.sbin/ppp/tcpmss.c
index ed7ef46..f8debc8 100644
--- a/usr.sbin/ppp/tcpmss.c
+++ b/usr.sbin/ppp/tcpmss.c
@@ -28,6 +28,8 @@
 
 #include <sys/param.h>
 
+#include <sys/socket.h>
+#include <net/route.h>
 #include <netinet/in_systm.h>
 #include <netinet/in.h>
 #include <netinet/ip.h>
@@ -54,6 +56,7 @@
 #include "filter.h"
 #include "descriptor.h"
 #include "mp.h"
+#include "iface.h"
 #ifndef NORADIUS
 #include "radius.h"
 #endif
@@ -93,7 +96,7 @@ tcpmss_LayerPush(struct bundle *bundle, struct link *l, struct mbuf *bp,
       ntohs(pip->ip_len) == plen && hlen <= plen &&
       plen - hlen >= sizeof(struct tcphdr))
     MSSFixup((struct tcphdr *)(MBUF_CTOP(bp) + hlen), plen - hlen,
-             MAXMSS(bundle->mtu));
+             MAXMSS(bundle->iface->mtu));
 
   return bp;
 }
diff --git a/usr.sbin/ppp/tty.c b/usr.sbin/ppp/tty.c
index 2727fec..773525c 100644
--- a/usr.sbin/ppp/tty.c
+++ b/usr.sbin/ppp/tty.c
@@ -333,6 +333,7 @@ tty_device2iov(struct device *d, struct iovec *iov, int *niov,
 static struct device basettydevice = {
   TTY_DEVICE,
   "tty",
+  0,
   { CD_VARIABLE, DEF_TTYCDDELAY },
   tty_AwaitCarrier,
   NULL,
diff --git a/usr.sbin/ppp/tun.c b/usr.sbin/ppp/tun.c
index f61f1f2..480e6c2 100644
--- a/usr.sbin/ppp/tun.c
+++ b/usr.sbin/ppp/tun.c
@@ -27,10 +27,12 @@
  */
 
 #include <sys/param.h>
-#ifndef __FreeBSD__
+
 #include <sys/socket.h>		/* For IFF_ defines */
+#ifndef __FreeBSD__
 #include <net/if.h>		/* For IFF_ defines */
 #endif
+#include <net/route.h>
 #include <netinet/in.h>
 #include <net/if_types.h>
 #include <net/if_tun.h>
@@ -68,6 +70,7 @@
 #include "ccp.h"
 #include "link.h"
 #include "mp.h"
+#include "iface.h"
 #ifndef NORADIUS
 #include "radius.h"
 #endif
@@ -89,7 +92,7 @@ tun_configure(struct bundle *bundle)
   }
 
   sprintf(ifr.ifr_name, "tun%d", bundle->unit);
-  ifr.ifr_mtu = bundle->mtu;
+  ifr.ifr_mtu = bundle->iface->mtu;
   if (ioctl(s, SIOCSIFMTU, &ifr) < 0)
       log_Printf(LogERROR, "tun_configure: ioctl(SIOCSIFMTU): %s\n",
              strerror(errno));
@@ -100,7 +103,7 @@ tun_configure(struct bundle *bundle)
 
   memset(&info, '\0', sizeof info);
   info.type = IFT_PPP;
-  info.mtu = bundle->mtu;
+  info.mtu = bundle->iface->mtu;
   
   info.baudrate = bundle->bandwidth;
 #ifdef __OpenBSD__
diff --git a/usr.sbin/ppp/udp.c b/usr.sbin/ppp/udp.c
index 6894e1e..8307a4a 100644
--- a/usr.sbin/ppp/udp.c
+++ b/usr.sbin/ppp/udp.c
@@ -154,6 +154,7 @@ udp_device2iov(struct device *d, struct iovec *iov, int *niov,
 static const struct device baseudpdevice = {
   UDP_DEVICE,
   "udp",
+  0,
   { CD_NOTREQUIRED, 0 },
   NULL,
   NULL,