Re: Connectivity Problem with WS-C3750G-24TS and Broadcom BCM5708C SLB

Hi Torsten,

I have a problem with Broadcom Smart Loadbalancing and Cisco WS-
C3750G-24TS.

We have a stack consisting of two Cisco WS-C3750G-24TS.
A Dell PowerEdge Server with two Broadcom BCM5708C Cards was
connected to the Stack; one Card per Switch. The two Cards were teamed
with Broadcom Smart Load Balancing, using the Broadcom Advanced
Control Suite.

I have been involved in a similar setup (in our case using a stack of
2 x 3750 48 port switches and MS Teaming on the Servers), and seen
something very similar, IE periods where things just "go to sleep"...
switch wide! It all depended on the MODE of teaming being used on the
Server. Now I am NOT a Server person, but was discovered a
configuration change had been applied on the Server end and was able
to come up with a work-around that did what we wanted for our setup
using the following.

If I understand it correctly, MS Teaming seems to provide about 4
possible configuration modes for Teaming operation (all using just 1
IP address on the server) -
1. Load balancing using Single MAC sharing.
2. Path Redundancy using Single MAC sharing.
3. Load balancing using 2 MAC's.
4. Path Redundancy using 2 MAC's.

When configured for Mode 1, we had an almost identical situation to
you, except in our case the switch just dumped its entire MAC address
table and refreshed (very slowly), which seemed to take quite a bit of
time, so it used to stop ALL traffic on the switch stack (IE all 96
ports) until something was done to sort out the issue.

My theory was that Mode 1 was presenting an IDENTICAL MAC on 2
different Switch ports, causing an issue for the 3750's MAC table.

We found that Mode 2 worked fine, which gave us what we really needed,
a backup or alternate path. Only 1 real path was ever active at any
one time, the other path NEVER saw the MAC of the server on it until
the first PATH had died.

The down side of this is that it also means you are vulnerable to the
Server not doing something stupid that re-enables path sharing (highly
possible with an MS environment).

Modes 3 & 4 should be fine as only 1 MAC per port was ever seen by the
3750.

So if you use Teaming for redundancy purposes, and your version of
Teaming allows this, and works the same as the MS way, then it should
be possible to get it to work.

Every about 20 minutes or so, the Dell Server was able to ping e.g.,
machines A, B and C, but not D, E and F.

Ours was a failure about every 20 minutes or so as well, except it
would knock down the entire stack and take 5-10 minutes to recover.

There is no log entry in the Cisco or in the Windows event log
correlating to the problem.

Nope, not a squeak anywhere on what was going on. Our only clue was
that Network access to the 3750 stack completely died until the MAC
table had been re-built, but by then everything looked fine again.


We upgraded the NIC Drivers, changed cables, without any result.
When we remove one of the Broadcom NIC connections, the connection
remains stable.

Exactly... its my guess you are getting a single MAC appearing on 2
different switch ports, and this is causing the switch to choke..

The strange thing is that we have a lot of similar configurations
(3750 Stack connected to Dell Servers with teamed Broadcom NICs)
running without any Problems.

How is the Teaming configured on these? We also had a set of Servers
using MS Teaming running fine for abut a year, but it was only when
new Servers were added in a different MODE of Teaming that the new
problem emerged.


IOS Version is 12.2(25)SEE2

Pretty much identical I Think , except we were at SEE3.


I believe that
the above configuration was running on that switch as well without
problems for months (I don't get always informed what our Serveradmins
are doing :-( )

Let me guess, they were "tweaking the way things were configured" to
get it to run better?.....;-)

Good luck.........................pk.


--
Peter from Auckland.
.

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