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Date: Mon, 25 Jun 2001 23:02:55 +0400
From: Yar Tikhiy <yar@freebsd.org>
To: audit@freebsd.org, net@freebsd.org
Subject: Long ether frames & MTU
Message-ID: <20010625230255.A11496@comp.chem.msu.su>
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Hi there,

While more and more Ethernet NIC drivers start supporting long
frames (>1518 bytes), the user/admin still cannot raise MTU on an
Ethernet interface above the 1500 byte limit due to outdated code
in net/if_ethersubr.c

Please review the following patch that removes the limitation, and
also substitutes predefined symbolic names for some numeric constants.

-- 
Yar

--- if_ethersubr.c	Wed Mar 14 01:00:32 2001
+++ /home/yar/if_ethersubr.c	Mon Jun 25 22:45:25 2001
@@ -677,8 +677,8 @@
 
 	if_attach(ifp);
 	ifp->if_type = IFT_ETHER;
-	ifp->if_addrlen = 6;
-	ifp->if_hdrlen = 14;
+	ifp->if_addrlen = ETHER_ADDR_LEN;
+	ifp->if_hdrlen = ETHER_HDR_LEN;
 	ifp->if_mtu = ETHERMTU;
 	ifp->if_resolvemulti = ether_resolvemulti;
 	if (ifp->if_baudrate == 0)
@@ -805,7 +805,7 @@
 		/*
 		 * Set the interface MTU.
 		 */
-		if (ifr->ifr_mtu > ETHERMTU) {
+		if (ifr->ifr_mtu > ETHERMTU + ifp->if_hdrlen - ETHER_HDR_LEN) {
 			error = EINVAL;
 		} else {
 			ifp->if_mtu = ifr->ifr_mtu;

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