On 3/22/2010 11:14 PM, Ray Van Dolson wrote:
On Mon, Mar 22, 2010 at 08:04:10PM -0700, Jay Hennigan wrote:
On 3/22/10 7:03 PM, Ray Van Dolson wrote:
We have two Dell PowerConnect M6220 switches (A1 and B1). They are not
cross-connected, but both have uplinks to the same subnet:
zfs1
/
+----+
| A1 |---------|
+----+ +-------+
| Cisco |------- linux1
+----+ +-------+
| B1 |---------|
+----+
/ \
esx1 esx2
There's a host hanging off of A1 (zfs1) and several ESX hosts hanging
off of B1 (esx1, esx2, etc). There's a host linux1 hanging off the
Cisco as well (actually many hosts, but for the sake of description
What's happening is, esx1/2 beging talking to zfs1. All is well for a
while... but at some point, zfs1's MAC address expires from the CAM on
the switch (I guess that is what is happening).
At that point, the Cisco begins forwarding the unicast packets to all
its ports. The result -- linux1, and all other hosts see the packets.
Occasionally, when we're dealing with a lot of traffic, this seriously
impacts performance.
Is the Cisco a router or a layer 2 switch? All hosts in the same IP
subnet? Subnet masks all match? Nothing doing proxy-arp?
My question here is.. what is the _right_ way to deal with this? This
"flooding" can continue for many minutes at a time.. it isn't until an
ARP reply eminates from zfs1 that the CAM table is populated again and
the broadcasting stops.
If these are layer 2 switches, ARP won't have anything to do with it.
If zfs1's MAC expires from the MAC address table on the cisco, it will
flood the next packet for that MAC. A1 will forward it to zfs1 or flood
if it too has expired the MAC.
When zfs1 replies, A1 forwards the reply to the cisco. At that point,
the cisco should re-install the MAC into its address table and the
flooding cease.
This should happen with a single packet.
Does this happen with any other hosts behind A1? Any interface errors
on any of the devices?
I wonder if zfs1 would send back an ARP response quicker were it not
behind an additional switch (the PowerConnect)...
If layer 2 switches, ARP doesn't have anything to do with it.
I'll have to find out how the Cisco's are configured. I wouldn't be
surprised if they're doing some Layer 3 though as I know some VLAN
routing is going on...
The Dell switches both seem to have "Routing Mode" enabled as well (but
proxy arp disabled).
There currently aren't any other hosts behind A1, but that would be a
good test. No interface errors currently.
Firmware is old on A1, so at this point I'm a little suspicious it's to
blame.
Just wanted to try and wrap my head around this first.
Thanks,
Ray
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In other multivendor LAN setups, We've noticed similar behavior and
enjoyed some success by synching the arp timers. That's worth a look if
you haven't already followed that line of investigation.
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