Changes devether's Max Trans Unit to 1500 From 1514. Linux drivers track it as 1500, and add on the header as needed. Plan 9 uses 1514, and includes the header. I don't particularly care one way or another. This way is a little easier for porting, but have no problem with changing it back (given a port to bnx2x's MTU code).

diff --git a/kern/drivers/dev/ether.c b/kern/drivers/dev/ether.c
index 9da3f38..b774889 100644
--- a/kern/drivers/dev/ether.c
+++ b/kern/drivers/dev/ether.c

@@ -447,7 +447,7 @@
 		error(Ebadctl);
 	}
 
-	if (n > ether->maxmtu)
+	if (n > ether->maxmtu + ETHERHDRSIZE)
 		error(Etoobig);
 	bp = allocb(n);
 	if (waserror()) {
@@ -489,7 +489,7 @@
 		runlock(&ether->rwlock);
 		nexterror();
 	}
-	if (n > ether->maxmtu && (bp->flag & Btso) == 0) {
+	if (n > ether->maxmtu + ETHERHDRSIZE && (bp->flag & Btso) == 0) {
 		freeb(bp);
 		error(Etoobig);
 	}

diff --git a/kern/drivers/net/bnx2x/bnx2x_dev.c b/kern/drivers/net/bnx2x/bnx2x_dev.c
index 8a3c8f9..9c9303a 100644
--- a/kern/drivers/net/bnx2x/bnx2x_dev.c
+++ b/kern/drivers/net/bnx2x/bnx2x_dev.c

@@ -480,15 +480,6 @@
 	edev->promiscuous = bnx2x_promiscuous;
 	edev->multicast = bnx2x_multicast;
 
-	/* Plan 9's MTU includes the header (e.g. 1514, instead of 1500).  Linux
-	 * drivers expect just the payload and not the header, and will add in the
-	 * 14 whenever it is needed.
-	 *
-	 * There might be issues when plan 9 code accesses maxmtu, now that it's
-	 * 1500 instead of 1514.  Keep a lookout for Etoobig in etherwrite.  What a
-	 * mess. */
-	edev->maxmtu -= ETHERHDRSIZE;
-
 	bnx2x_reset(ctlr);
 
 	return 0;

diff --git a/kern/drivers/net/ether82563.c b/kern/drivers/net/ether82563.c
index 93a65e2..8ce14da 100644
--- a/kern/drivers/net/ether82563.c
+++ b/kern/drivers/net/ether82563.c

@@ -1924,7 +1924,7 @@
 	edev->irq = ctlr->pcidev->irqline;
 	edev->tbdf = pci_to_tbdf(ctlr->pcidev);
 	edev->mbps = 1000;
-	edev->maxmtu = ctlr->rbsz;
+	edev->maxmtu = ctlr->rbsz - ETHERHDRSIZE;	/* MTU doesn't include header */
 	memmove(edev->ea, ctlr->ra, Eaddrlen);
 
 	/*

diff --git a/kern/include/ip.h b/kern/include/ip.h
index ea40e01..b779371 100644
--- a/kern/include/ip.h
+++ b/kern/include/ip.h

@@ -1006,7 +1006,7 @@
 enum {
 	Eaddrlen = 6,
 	ETHERMINTU = 60,	/* minimum transmit size */
-	ETHERMAXTU = 1514,	/* maximum transmit size */
+	ETHERMAXTU = 1500,	/* maximum transmit size */
 	ETHERHDRSIZE = 14,	/* size of an ethernet header */
 };