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mac table of switch (PTCP platform) isn't completed that is why traffic has pulse nature

Publication Date:  2012-07-27 Views:  51 Downloads:  0
Issue Description

Throughput of PTCP platform has a pulse nature. You can see pulse nature of traffic according to t graph on the pic 1(see attachment):




Alarm Information




There is no any alarm except graph (pic 1) (see attachment)…




Handling Process

For elimination this problem You have to increase mac-address aging time to from default value 300 seconds to 1200 seconds.

Root Cause




For clear understanding, see topology scheme (pic 2)
According to design of PTCP, incoming and outgoing traffic are passed through different VLANs (this is key point).

Packets from PTCP-S9306 are sent to the Load Balancer Unit (LBU) constantly through L2 switch F120. According to switching algorithm F120 learns its mac address of L3 switch PTCP-S9306 AAA-AAA-AAA, but in can’t learn MAC address BBB-BBB-BBB, because there are no any reverse traffic in this VLAN. So in this situation F120 has to broadcast all incoming from Internet traffic. This caused “broadcast collapse” of PTCP platform (because traffic is huge). This situation exists until ARP entry on the S9306 (ip:X.X.X.X - - - MAC:BBB-BBB-BBB) has been expired. (As You remember default expire time is 1200 seconds). When ARP entry expired, S9306 send out broadcast ARP request (who has MAC: BBB-BBB-BBB).After arp-request received by LBU, LBU reply by arp-response (ip:X.X.X.X - - -MAC:BBB-BBB-BBB). During this arp-response goes through F120 switch, F120 learn MAC address (MAC: BBB-BBB-BBB). From this moment F120 knows MAC: BBB-BBB-BBB and “broadcast collapse” stops. As You can remember default mac aging time is 300 second, so during next 300 second there is no any broadcast storm. After 300 seconds are elapsed mac entry (port 2 – MAC:BBB-BBB-BBB) is deleted and broadcast storm begins again (until ARP entry of S9306 will be expired). And this process has circle nature. That is why traffic throughput has pulse nature!

Suggestions

Because design of PTCP platform we can’t change we have to tuning mac-address aging time for elimination pulse affect of throughput!

 

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