GigabitEthernet Testbed over Dark Fiber

3. Monitoring Gigabit Interfaces
Monitoring the Gigabit interface.
To monitor with SNMP a highly loaded gigabit
interface in a Cisco Catalyst 3550 it is necessary to
take in consideration that they have just 32 Bit
SNMP counters. If the interface is fully loaded with
1 Gigabit/s traffic the counter resets every 34
seconds.
(2^32 * 8) / 10 9 = 34.35 second
In consequence it is necessary to poll the
interface at least every 30 seconds. Taking in
consideration that when the switch is heavily loaded
the switch can't respond to the SNMP request in
time we have decided to poll the interface every 20
seconds.
The monitoring machine was a RedHat Linux
2.4.19, using UCD-SNMP version 4.2.4 to fetch the
data, and RRD-tool 1.0.40 to store and graph the bit
rates and packet rates. Because in CRONTAB we
can't setup to run the data fetching script every 20
seconds we used the following script:
#!/bin/bash
while true; do
/var/local/flows/giga-test/scripts/snmp-datastore
sleep 20
done
The snmp-data-store script pools the gigabit
interface and store the data in rrd's.
IN=$(snmpget 217.73.171.3 public 2.2.1.10.26 |
awk "{print \$4 ;}")
OUT=$(snmpget 217.73.171.3 public
2.2.1.16.26 | awk "{print \$4 ;}")
INpk=$(snmpget 217.73.171.3 public
interfaces.ifTable.ifEntry.ifInUcastPkts.26 | awk
"{print \$4 ;}")
OUTpk=$(snmpget 217.73.171.3 public
interfaces.ifTable.ifEntry.ifOutUcastPkts.26 |
awk "{print \$4 ;}")
DATA=`date +%s`
rrdtool update /var/local/flows/gigatest/rrds/c3550.rrd
$DATA:$IN:$OUT:$INpk:$OUTpk
Every 5 minute one script create the graphic in
the form of a GIF picture.
To visualize the bit rates we use the following
rrdtool command:
rrdtool graph gigabits20.gif \
--start -86400 -t "Giga 20 sec" \
-w 600 -h 400 --base 1000 \
DEF:i=c3550.rrd:in:AVERAGE \
CDEF:inb=i,8,* \
DEF:o=c3550.rrd:out:AVERAGE \
CDEF:outb=o,8,* \
CDEF:outbn=outb,-1,* \
AREA:inb#00ff88:"IN traf" \
COMMENT:Min \
GPRINT:inb:MIN:%lf%s COMMENT:bps
\
COMMENT:Average \
GPRINT:inb:AVERAGE:%lf%S
COMMENT:bps \
COMMENT:Max \
GPRINT:inb:MAX:%lf%s
COMMENT:bps \
AREA:outbn#ff8800:"Out traff" \
COMMENT:Min \
GPRINT:outb:MIN:%lf%s
COMMENT:bps \
COMMENT:Average \
GPRINT:outb:AVERAGE:%lf%S
COMMENT:bps \
COMMENT:Max \
GPRINT:outb:MAX:%le%s
COMMENT:bps \
HRULE:0#000000
4. Tests
4.1 Connectivity test
Before any exhaustive test could begin we had to
test connectivity between the two switches.
The estimated distance of 110km is slightly over
the 100km range of the product but fortunately after
connecting the optical fiber the connected LED lit
up. CDP also showed the other end switch.
4.2 Layer 3 connectivity test
After some basic configuration a IP connectivity
test could be performed and ping reported 2 ms.
After configuring a routing loop and injecting
some traffic, interface utilization was brought up to
over 95%. Ping reported an average 15 ms and still
with no packet drops. The switch and interfaces are
performing quit well.
4.3 Monitored Heavy load test
50