Broadcast

Unanswered Question
Jun 14th, 2009

1.I have a switch network with like 5 vlans configured. I notice ther is a broadcast on the network because local ping is return with high latency, how do I troubleshoot, detect and Isolated the source.

2.On Vlan 2 on my root bridge, below is my out put of "sh int vlan 2"

TEST#sh int vl 2

Vlan2 is up, line protocol is up

Hardware is Cat6k RP Virtual Ethernet, address is 0018.746a.a07c (bia 0018.746a.a07c)

Description: ######

Internet address is X.X.X.X/24

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:00:00, output never, output hang never

Last clearing of "show interface" counters 1d16h

Input queue: 1/75/208359/206541 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 1967000 bits/sec, 1626 packets/sec

5 minute output rate 1512000 bits/sec, 1368 packets/sec

596185378 packets input, 138497387183 bytes, 0 no buffer

Received 1557287 broadcasts (127494 IP multicast)

0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

398327426 packets output, 129099292310 bytes, 0 underruns

0 output errors, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

Looking at the "Received 1557287 broadcasts (127494 IP multicast)", does it mean hosts on this vlan are generating the broadcast traffic.

3. A switch directly connected to my root bridge on G0/26, and host on the other ports, has the out put of the "sh int G0/26" as

YYYYYY#sh int g0/26

GigabitEthernet0/26 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet, address is 001a.2fc3.861a (bia 001a.2fc3.861a)

Description: ####Connection to Core Switch###

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive not set

Full-duplex, 1000Mb/s, link type is auto, media type is 1000BaseSX SFP

input flow-control is off, output flow-control is unsupported

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:00:00, output 00:00:09, output hang never

Last clearing of "show interface" counters 1d22h

Input queue: 6/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 1320000 bits/sec, 1355 packets/sec

5 minute output rate 1401000 bits/sec, 1242 packets/sec

540636824 packets input, 3354328902 bytes, 0 no buffer

Received 5856548 broadcasts (0 multicast)

0 runts, 0 giants, 0 throttles

5610 input errors, 5610 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 2184813 multicast, 0 pause input

0 input packets with dribble condition detected

391530257 packets output, 1177316497 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 PAUSE output

0 output buffer failures, 0 output buffers swapped out

Looking at the "Received 5856548 broadcasts (0 multicast)" also, does this mean the switch is receiving the broadcast from the core on G0/26 or what.

4.When a switch receives a broadcast on an interface and broadcast it on others, will the traffic categorised as "5 minute input rate 1320000 bits/sec, 1355 packets/sec (or

5 minute output rate 1401000 bits/sec, 1242 packets/sec), or will it be categorised as

" Received 5856548 broadcasts (0 multicast)"

I have this problem too.
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Giuseppe Larosa Sun, 06/14/2009 - 22:02

Hello Just,

the interface counters should account for all packet/frame type received/transmitted.

When evaluating the level of broadcast on an interface we should compare the total number of packets rx

540636824 packets input,

with the total broadcast received

Received 5856548 broadcasts (0 multicast)

As you can see on this interface broadcast is 1,08 % of total traffic and this can be acceptable and not a sign of a problem.

This is interface is also lightly used load 1/255.

>> I notice ther is a broadcast on the network because local ping is return with high latency, how do I troubleshoot, detect and Isolated the source.

There can be other reasons for slow answer to ping a link can be congested for example or the target device can be busy (high cpu usage).

Hope to help

Giuseppe

tarnhundal Tue, 06/16/2009 - 22:07

hi ,

If u want to control it then u can implement storm control on interfaces . i think it wll help u to control broadcast.

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