[Bridge] [BUG] Dropping fragmented IP packets within VLAN frames on bridge

Adam Osuchowski adwol at zonk.pl
Fri May 25 01:17:50 PDT 2007

There is a problem with fragmented IP packet sent within 802.1Q tagged
ethernet frame through bridge. Problem exists when conntrack is enabled
(i.e. nf_conntrack_ipv4 module is loaded). Then, such packets are not
fragmented again (after prior reassembling on bridge device) during
passing it to bridge enslaved NIC. It cause MTU exceeding and as a result
dropping packet.

Problem exists from kernel version 2.6.17 to inclusive.

Below, there is a patch to fix it.


--- linux-	2007-05-25 09:56:15.000000000 +0200
+++ linux-	2007-05-25 10:11:42.000000000 +0200
@@ -731,7 +731,7 @@
 static int br_nf_dev_queue_xmit(struct sk_buff *skb)
-	if (skb->protocol == htons(ETH_P_IP) &&
+	if ((skb->protocol == htons(ETH_P_IP) || IS_VLAN_IP(skb)) &&
 	    skb->len > skb->dev->mtu &&
 		return ip_fragment(skb, br_dev_queue_push_xmit);

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