Hi Jesse,
I just came across this:
http://www.mail-archive.com/[email protected]/msg14547.html
I'm seeing a problem with this currently under Xen's bridging
configuration.
Basically, with the patch, packets are being dropped at this point in
net/bridge/br_forward.c:
---
int br_dev_queue_push_xmit(struct sk_buff *skb)
{
/* drop mtu oversized packets except gso */
if (packet_length(skb) > skb->dev->mtu && !skb_is_gso(skb)) {
kfree_skb(skb);
--
What's happening that a 1500 byte packet comes in from e1000, onto the
bridge and is to be forwarded to a device whose mtu is 1500. Because the
CRC hasn't been stripped, skb->len is 1504 and the packet is dropped.
One option is to fix this specific problem is to subtract the CRC
length from skb->len in e1000, another is to raise the MTU on the
receive side of Xen's loopback interface. I've attached a patch for the
latter, but I've no real opinion on which is more correct.
Cheers,
Mark.
--- ./xen/netback/loopback.c.jumbo-mtu-on-vif 2006-07-20 16:21:52.000000000 +0100
+++ ./xen/netback/loopback.c 2006-07-20 16:23:08.000000000 +0100
@@ -161,16 +161,6 @@
NETIF_F_IP_CSUM);
SET_ETHTOOL_OPS(dev, &network_ethtool_ops);
-
- /*
- * We do not set a jumbo MTU on the interface. Otherwise the network
- * stack will try to send large packets that will get dropped by the
- * Ethernet bridge (unless the physical Ethernet interface is
- * configured to transfer jumbo packets). If a larger MTU is desired
- * then the system administrator can specify it using the 'ifconfig'
- * command.
- */
- /*dev->mtu = 16*1024;*/
}
static int __init make_loopback(int i)
@@ -193,6 +183,16 @@
loopback_construct(dev2, dev1);
/*
+ * We only set a jumbo MTU on vif0.0. Otherwise the network
+ * stack will try to send large packets that will get dropped by the
+ * Ethernet bridge (unless the physical Ethernet interface is
+ * configured to transfer jumbo packets). If a larger MTU is desired
+ * then the system administrator can specify it using the 'ifconfig'
+ * command.
+ */
+ dev1->mtu = 16*1024;
+
+ /*
* Initialise a dummy MAC address for the 'dummy backend' interface. We
* choose the numerically largest non-broadcast address to prevent the
* address getting stolen by an Ethernet bridge for STP purposes.
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