Troubleshooting Network slow Issues
Case 1: The switchports had an extremely high collision count
Looked at the Cisco switches connecting between
the guardhouse and main building.
Show interface shows the switchports had an extremely high collision
count. Looked at the
configuration of the ports and they were only set to half duplex.
Changed both ends to full duplex forced.
Traffic was flowing without errors.
The connection was faster.
Case 2: Cisco switch logs flapping
Symptoms: 1. Clients keeps receiving time out message when they access
Microsoft SQL server.
2. TM Vista program freezes or gets Error testing for active program
3. Ping gets time out randomly.
telnet to the switch that the server is connecting to.
Use show loggings to check any errors>
We found numerous errors:
008276: *May 22 13:21:19: %SW_MATM-4-MACFLAP_NOTIF: Host 0008.02a2.414d in
vlan 1 is flapping between port Po3 and port Gi0/9
008277: *May 22 13:22:12: %SW_MATM-4-MACFLAP_NOTIF: Host 0023.7dea.fe76 in
vlan 1 is flapping between port Po4 and port Po3
008279: *May 22 13:22:43: %SW_MATM-4-MACFLAP_NOTIF: Host 000d.939d.d87c in
vlan 1 is flapping between port Po3 and port Gi0/18
Investigated and found that the servers had two NICs in two separate
switches that were not joined via port aggregation.
Removed the secondary teamed NIC and half the errors went away.
The other errors that remained only had a single NIC in the network.
Continued troubleshooting and unable to find anything unusual.
Decided to get Cisco TAC involved and opened case.
Spoke with multiple techs about the situation.
Took debugs of spanning tree and found that there was multiple
convergences occurring on the network at the same time.
Was unable to see through the CLI without the debug because it was
occurring so fast. Traced it
down to the switches and found switch 3560_7 to have a device plugged into
gi0/1 that is running BPDU (stand for bridge protocol data unit. BPDUs are
data messages that are exchanged across the switches within an extended LAN
that uses a spanning tree protocol topology. BPDU packets contain
information on ports, addresses, priorities and costs and ensure that the
data ends up where it was intended to go. BPDU messages are exchanged across
bridges to detect loops in a network topology. The loops are then removed by
shutting down selected bridge interfaces and placing redundant switch ports
in a backup, or blocked, state) and rebroadcasting MAC addresses on the
network, causing the mac-address table to update with the wrong routing
information. Traced down what
was in port gi0/1 in switch 3560_7.
A Crestron system was plugged into the port.
As soon as the port was disabled, the network became stable again and
the errors and timeouts went away.
When the port was enabled, the issues started occurring again.
Tried to turn bpdugaurd on but it kept disabling the port.
Enabled bpdufilter but the mac-address table was learning outside of
BPDU. Finally, we moved the
system to a VLAN of its own so it doesn't interfere with the rest of the
network. Accessing SQL, Vista
program works as normal. Ping gets 0 lost.
Pano broadcasts a lot ARP requests
client complained the network is too slow. We used Wireshark and capture
found that over 60% of the packets in both files were from the same source,
a Pano server. It appears that
host is broadcasting ARP request out for everything in the local data
subnet. This generally doesn't
happen unless that machine is trying to communicate with everyone on the
local subnet (not a typical behavior).
There are 4 Pano devices (VMware VMs) in the Library and they are
turned off every night. When they are off, the server tries to wake up them
by sending packets. Keeping those devices on reduces the broadcasts.
Machines infected with viruses or worms often having a scanning mechanism
looking for other machines to infect which causes a high volume of ARP
Case 4: It could be a bad cable. Please check this page for more
Server uses over 75% bandwidth of the switch
Post your questions, comments, feedbacks and suggestions
Contact a consultant
Domain PC is taking too long to boot up