Gergely Madarasz wrote:
On Mon, Jan 10, 2005 at 10:05:56AM -0500, Neil Horman wrote:
Gergely Madarasz wrote:
Hello,
I've got a very strange problem. Lately I've been setting up my linux
servers for network (layer2) redundancy with a bridge interface containing
two ethernet interfaces connecting to two switches. So far I didn't have
any problems with it, but now a very strange thing happens with a new
server I'm installing. The server is an ibm x346 having two onboard
BCM5721 cards, the switches are cisco 3550, and I've tested with kernel
versions 2.6.10 and 2.4.28.
The bpdu's from the cisco switches simply cannot be seen on the server,
causing loops in l2 traffic. I've tested with sticking a hub between the
c3550 and the server, the switch sends out the bpdu's, but they are not
seen by linux (running tethereal). This happens only on eth0, on eth1
everything seems fine. Any IP traffic on eth0 goes through, no packet
loss, no errors.
And something even more strange: if I do an
ifconfig eth0 0 up; brctl addif br0 eth0;
it seems to be working fine, if I do it the other way
round, then the bpdu's sent by the switches are lost somewhere.
Considering all these, the problem seems to me a strange interaction
between the bridge driver, the tg3 driver and the hardware in question.
It looks to me like either order should work just fine, as long as the
IFF_PROMISC flag isn't cleared when you bring up the interface. Is
IF_PROMISC clear in ifconfig after you issue your ifconfig eth0 up command?
ifconfig has never showed PROMISC on either of my bridged servers.
ip shows it though. I noticed this before but couldn't find the reason and
didn't seem important.
This is on a machine with working bridge:
# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:09:6B:49:89:80
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
...
# ip link list eth0
2: eth0: <BROADCAST,MULTICAST,PROMISC,UP> mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:09:6b:49:89:80 brd ff:ff:ff:ff:ff:ff
And this is on the problematic machine:
# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0D:60:55:3B:02
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
....
# ip addr list eth0
2: eth0: <BROADCAST,MULTICAST,PROMISC,UP> mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:0d:60:55:3b:02 brd ff:ff:ff:ff:ff:ff
Strange. My concern was that the tg3 interface has its hardware reset
whenever its set to be up, and part of that is a resetting of its
receive mode. If for some reason IFF_PROMISC was cleared after you set
it using brctl, the interface might be taken out of promisc mode. Do
you have any iptables rules running that might drop bpdus?
And even if didn't get promisc, tcpdump or tethereal would have made it
so, when I was looking for the bpdu packets. Tethereal shows only this:
Thats not entirely true. ethereal/tcpdump/etc use the PF_PACKET
interface, which talks directly to the driver to set the receive list,
and doesn't always go through the device layer, which is where
IFF_PROMISC gets asserted. Agruably it should set promisc, but not
doing so doesn't prevent ethereal and friends from capturing in
promiscuous mode.
0.000000 00:0d:60:55:3b:02 -> 01:80:c2:00:00:00 STP Conf. Root =
65535/00:0d:60:55:3b:02 Cost = 0 Port = 0x8001
Greg
--
/***************************************************
*Neil Horman
*Software Engineer
*Red Hat, Inc.
[EMAIL PROTECTED]
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*http://pgp.mit.edu
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