How many broadcasts are too many broadcasts.

eclinton · ‎11-27-2012

Hello everyone,

1 day and 2 hours ago I cleared the counters on a SVI on a 6509 running IOS. Since then the interface has received 1386034 broadcasts (89547 IP multicasts). I have a few questions about the interface's broadcast counter:

1. Is there a magical formula to figure out if there are too many broadcasts occurring on the vlan?

1. What traffic is being counted as broadcasts, is it strictly all F's or all 255'3 or is ARP and HSRP Multicast and other protocols counted as broadcasts?

I believe the flooding of broadcasts is filling the interface input queue and causing drops.

Thanks

Erik,,,,,,

VlanXX is up, line protocol is up

Hardware is EtherSVI, address is 0019.a9f8.f000 (bia 0019.a9f8.f000)

Description: Business Partner Network

Internet address is x.x.x.x/x

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 supported

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

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

Last clearing of "show interface" counters 1d02h

Input queue: 0/4096/917/917 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 33000 bits/sec, 18 packets/sec

5 minute output rate 4000 bits/sec, 7 packets/sec

L2 Switched: ucast: 28271274 pkt, 14513790452 bytes - mcast: 1386339 pkt, 104250673 bytes

L3 in Switched: ucast: 522593 pkt, 511617457 bytes - mcast: 0 pkt, 0 bytes mcast

L3 out Switched: ucast: 218919 pkt, 17736207 bytes mcast: 0 pkt, 0 bytes

2271895 packets input, 639427117 bytes, 0 no buffer

Received 1386034 broadcasts (89547 IP multicasts)

0 runts, 0 giants, 0 throttles

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

417206 packets output, 35944753 bytes, 0 underruns

0 output errors, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

VlanXX is up, line protocol is up
Hardware is EtherSVI, address is 0019.a9f8.f000 (bia 0019.a9f8.f000)
Description: Business Partner Network
Internet address is x.x.x.x/x
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 supported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters 1d02h
Input queue: 0/4096/917/917 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 33000 bits/sec, 18 packets/sec
5 minute output rate 4000 bits/sec, 7 packets/sec
L2 Switched: ucast: 28271274 pkt, 14513790452 bytes - mcast: 1386339 pkt, 104250673 bytes
L3 in Switched: ucast: 522593 pkt, 511617457 bytes - mcast: 0 pkt, 0 bytes mcast
L3 out Switched: ucast: 218919 pkt, 17736207 bytes mcast: 0 pkt, 0 bytes
     2271895 packets input, 639427117 bytes, 0 no buffer
     Received 1386034 broadcasts (89547 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     417206 packets output, 35944753 bytes, 0 underruns
     0 output errors, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out

benjammin · ‎11-27-2012

Where are you seeing the drops?

eclinton · ‎11-27-2012

Hi Benjamin,

here is the number of drops and flushes since I cleared the counters.

Input queue: 0/4096/917/917 (size/max/drops/flushes); Total output drops: 0

Peter Koltl · ‎11-27-2012

I've seen 16 broadcast packets per second in a big VLAN without any problems. You should assess the quantity based on the number of hosts in the VLAN. Perform a packet capture and you can analyze the top broadcasters in Wireshark.