Does anyone know if switches will go into STP learning mode during the time when the root bridge sends Configuration BPDUs with the Topology Change bit set to 1? I understand that the Topology Change process is used to age out the mac-address tables of switches but do these switches go in to the learning state instead of remaining in the forwarding state? Any advice is greatly appreciated!
The switch that has the topology change will go through the listening and learning phases on that particular interface but the others will just age out their mac addresses a little faster. If they all went into the learning phase your whole network would go down everytime any switch had a topology change.
This definitely helps. Are you saying that for switches running 802.1D STP and don't have portfast configured on the user ports will recalculate spanning tree topology if a users plug their devices into the access ports?
"An important point to consider here is that a TCN does not start a STP recalculation. This fear comes from the fact that TCNs are often associated with unstable STP environments; TCNs are a consequence of this, not a cause. The TCN only has an impact on the aging time. It does not change the topology nor create a loop. "
I believe you are correct that TCN does not start an STP recalculation but, rather, are the consequence of recalculation. According to the STP chapters of the CCIE LAN Switching book, a switch generates TCN if it has a port that transitions to either the forwarding state or the blocking state. Can we agree that these state transitions are caused by either loss of BPDUs (past the max-age time) or introducing a switch that generates more superior BPDUs into the network?
[toc:faq]The ProblemOn traditional switches whenever we have a trunk
interface we use the VLAN tag to demultiplex the VLANs. The switch needs
to determine which MAC Address table to look in for a forwarding
decision. To do this we require the switch to do...
[toc:faq]Introduction:Netdr is a tool available on a RSP720, Sup720 or
Sup32 that allows one to capture packets on the RP or SP inband. The
netdr command can be used to capture both Tx and Rx packets in the
software switching path. This is not a substitut...
IntroductionOSPF, being a link-state protocol, allows for every router
in the network to know of every link and OSPF speaker in the entire
network. From this picture each router independently runs the Shortest
Path First (SPF) algorithm to determine the b...