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New Member

rapid spanning tree edge and link ports

Hi all, can anyone tell me why rapid spanning tree has these 2 types of ports, what does it exactly do differently on each port?

6 REPLIES

Re: rapid spanning tree edge and link ports

Carl,

You have two kinds of ports:

- ports connected to other bridges. If both bridges run RSTP or MST, there is some kind of negotiation between them and you have fast convergence.

- ports connected to "end devices" (routers, stations etc...). RSTP has no peer on those ports and cannot do any negotiation. You need to explicitly identify those ports as "edge", by configuring portfast on them. In that case, RSTP/MST will put those links immediately to forwarding, without expecting anything from a peer.

Regards,

Francois

New Member

Re: rapid spanning tree edge and link ports

Hi There, thanks for that, however I already read that in my cisco book,

Does the edge port only come into use when you put portfast on them? I gather they still send and receive bpdu's with portfast?

Also on the link type ports that connect to other switches, do they forward straight away or do they wait a few seconds?

New Member

Re: rapid spanning tree edge and link ports

no, ports in portfast state do not participate in any BPDU information.

the ports connecting to other switches do not forward straight away, however when you configure uplink-fast feature these ports forward straight away without going through the spt LST/LRN/FWD stages.

steve knockswell

Re: rapid spanning tree edge and link ports

edge port = IEEE terminology for a port that has no STP peer and that cannot introduce a loop = port on which Cisco wants you to configure portfast;-)

About the behavior of portfast vs non-portfast port, see my previous post. Portfast port go immediately to forwarding, regular ports (non portfast), go forwarding depending on the STP rules.

Ports configured for portfast still run STP, they send BPDUs (but don't expect any, again because they are supposed to have no peer).

F.

New Member

Re: rapid spanning tree edge and link ports

Hi There

thanks for that, lastly, if im running rstp, Is the only way you define them as an edge port by adding portfast to them? and also when you say portfast ports send bpdu's but do not expect them, I gather they still listen for bpdu's? so they could still prevent a loop?

New Member

Re: rapid spanning tree edge and link ports

Hi Carl,

Configuring portfast on an edge port will not define it as an edge port. The term edge port is used to describe a port that is connected to an end user/router or a device(s) that will not create a loop in the network. Edge ports have nothing to do with BPDUs, point to point ports will work with BPDUs. Link-type Point to point ports is the term used for the links that are connecting the switches together.

Hope this helps, read through ftallet comments, this also explains the process and functionality.

Cheers,

Garry

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