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BPDU Size...

Hello everyone, simple and plain question.... Can TCN BPDU's reach 1500 bytes in size? suddenly when we attach a new device to the topology we can see an increment on the traffic and the are all 1500 bytes in size, we assume they are TCN BPDU's (at least BPDU's) because they are sent to the 01:80:C2:00:00:00 address.

Cheers!

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Cisco Employee

Re: BPDU Size...

Antonio,

According to the 802.1D standard, TCN BPDUs are very small - the TCN message itself is only 4B long. Because of framing, the entire Ethernet frame is 6 (DSTMAC)+6 (SRCMAC)+2 (LEN)+3 (LLC)+4 (TCN)+4 (FCS)=25B long which means it needs to be stuffed to the minimal size of 64 bytes. I see no reason for a TCN to be blown up to 1500 bytes.

A packet capture in this case would certainly elucidate things further.

Best regards,

Peter

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