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Apricot2001

Effectiveness of VLAN

Chan Wai Kok (wkchan@mmu.edu.my)

Faculty of Information Technology

Salim Beg (salim@mmu.edu.my) Faculty of EngineeringMultimedia University

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The benefit of VLAN

• Simplify the process of add, moves and changes• Provide broadcast, multicast traffic isolation by

grouping similar traffic types to a VLAN.• Provide some form of security

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Goals of this presentation

• To find out the broadcast traffic trend• To study the effectiveness of VLAN in broadcast

isolation

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Why Broadcast isolation is important ?

• On a 1 Gbps capacity backbone network• If 1% traffic is (broadcast + multicast + unknown

unicast), all end stations with 10Mbps link may be congested (but backbone have more capacity!!!)

• Broadcast frames will take up CPU resources. E.g On Pentium 120Mhz, – 1000 broadcast pps :- 15 % CPU resource– 3000 broadcast pps :- 28 % CPU resource

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Related Work(Will E. Leland & Daniel V Wilson Bellcore 1989 - 1990)

• collected LAN traffic data for long time scale and analyzed the trend

• Their showed that there is a great disparity in the values of peak to mean ratio for packet arrival rate. (73 to 861 for 5 sec to 5 milisec respectively)

• LAN traffic is Bursty • Focus on behavior of total Ethernet traffic

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LAN Traffic (hourly)

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LAN Traffic (busiest hour)

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LAN Traffic (by minutes)

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LAN Traffic (Peak to mean ratio)

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Analysis Method

• Collect network traffic from few different IP Subnet and check the broadcast plus multicast traffic quantity.

• Run an IP Multicast application• See how it’s effect the broadcast plus multicast

traffic in the IP subnet.• Make some conclusions on the result

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Network Setup

• A Pentium PC is used as a network analyzer• Traces are taken for a few days• Network consists of WinNT servers and Win95 PCs.• Each IP subnet consists of 60, 85 and 45 hosts

respectively. 3 different labs.• Two Labs are is fully used during office hour. • Students accessing WinNT server to work• No Novell Server (future is IP)

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Type of Packets Detected

• ARP request• Spanning Tree Frame (hello frame)• Netbios• SAP• IP Multicast Solicitation

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Traffic statistic

• Average bandwidth (extremely low)– 1413, 1761, 1381 bps (office hour)– 809, 789, 406 bps (non office hour)

• Maximum bandwidth (1 % of 10Mbps)– 31920, 125408, 130752 bps (office hour)– 29824, 70640, 38608 bps (non office hour)

• Majority of the traffic is background traffic• Generally, broadcast traffic is very low

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Traffic Statistic (no IP Multicast)

Broadcast traffic (no IP Multicast)

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1 2247 4493 6739 8985 11231 13477 15723 17969 20215

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Traffic Statistic (no IP Multicast)

Broadcast traffic (no ip mcast)

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1 54

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7

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21

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26

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31

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74

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79

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84

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90

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95

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Traffic Statistic (no IP Multicast)

Broadcast traffic (no IP Multicast)

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1 7

13

19

25

31

37

43

49

55

61

67

73

79

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91

97

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Traffic Statistic with IP Multicast application

• One IP Multicast Channel sending audio and text.• Average bandwidth :- 112 Kbps• Maximum Bandwidth :- 155 Kbps• Dramatic increased of (broadcast plus multicast)

bandwidth when IP Multicast is ran.• Traffic isolation will required IP Multicast VLAN

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Traffic Statistic with IP Multicast application

Traffic Statistic with IP Multicast Application

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27

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18

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22

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IP Multicast VLAN

• Router will duplicate IP Multicast packet to all IP Subnet that joined in IP Multicast group

• Some switch ports have multiple IP Subnet VLAN memberships. Therefore, may receive in duplicated IP Multicast packet

• IP Multicast VLAN is patented by 3com US Patent No: 5,818,838

• Term as IGMP spoofing• Dynamic filtering of IP Multicast group at switch port

level.

• Available in many commercial switches.

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IP Multicast Application

• Who is running IP Multicast at the 1st place ? • A 4.5 year studies on MBone traffic shows• 90% of users joined multicast group less than 74

times• top 1% joined MBone group > 350 times• 20% IP addresses - at least 1 hour per connection• 70% IP addresses :- average 1 min per connection

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IP Multicast Application

• Over 4.5 year• 20% of users joined MBone more than 1 day• 5% of users joined > 300 hours• A total of 33,545 unique IP is seen in 4.5 year• Jan 1998 :- 10,600 unique IP seen• ( > 20,000 IP didn’t joined any multicast session for

more than 1 year)• Jan 1999 :- 5,000 unique IP seen

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Conclusion

• When no IP Multicast application• Total Broadcast and multicast traffic is very low• problem of broadcast isolation does not arise at the

first place• VLAN is of little use

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Conclusion

• When IP Multicast is deployed• Dramatic increase in mean bandwidth• VLAN is useful only when IP Multicast application is

deployed• Make sure that current/future switch support IP

Multicast VLAN• However, IP Multicast application is still not popular

yet.• Studies have shown MBone is growing slowly and it

uses is not widespread.

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References

• http://imj.ucsb.edu/publications.html– BGPK. Almeroth, "A Long-Term Analysis of Growth and Usage

Patterns in the Multicast Backbone (MBone)", IEEE INFOCOM '00, Tel Aviv, ISRAEL, March 2000

• http://www.patents.ibm.com• http://www.argreenhouse.com/papers/wel/

– Will E. Leland, Daniel V. Wilson, “High Time-resolution Measurement and Analysis of LAN Traffic: Implications for LAN Interconnection,” Proceedings IEEE Infocom 1991, Bal Harbour, Florida, April 1991, pp.1360-1366. building and forwarding

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Question ??

Question can be forwarded to wkchan@mmu.edu.my