spanning tree - What flags are used in BPDUs in STP ...

Note that true TCN BPDUs were only used in the original STP. RSTP uses RST BPDUs with the TC bit set which have message/max age fields and are discarded when aged out. True TCN BPDUs have no age fields, but as far as I understand it, they're not forwarded. A bridge receiving a TCN BPDU may (and probably will) decide to send TCN BPDUs on its own ... Wenn ein Stamm die TCN-BPDU empfängt, sendet er eine Konfigurations-BPDU-Nachricht an alle Ports, wobei das Topologieänderungsflag auf 1 gesetzt ist. Switches, die diese BPDU am Root-Port empfangen, filtern die Datenbank und generieren ihre eigenen Konfigurations-BPDUs an bestimmten Ports. Dies breitet sich den Baum bis zum Ende des Pfades aus. After the TCN BPDU has reached the root bridge, the root bridge will send out configuration BPDU with TC bit set. The root does this for MaxAge + FWD_DELAY seconds which is 20 + 15 seconds by default, for a total of 35 seconds. When the switches receive this BPDU with TC set, they will shorten the timeout of the MAC address table to flush out stale entries. The timeout is then set to 15 ... TCN (topology change notification) BPDU packet is layer 2, Ethernet(I) packet. There are minor differences in structure of BPDU packet, depending on hardware vendor. Here, in this example, I'm using CISCO implementation. Ethernet header should always have destination address set to 01:80:C2:00:00:00 (STP multicast address). CCNP Quick Reference - Free download as PDF File (.pdf), Text File (.txt) or read online for free. GOOD

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