Using STP to create p2p channels
In networks where switches are used with limited memory resources used to store mac-addresses, or the time of convergence of the STP-protocol does not suit, you can use a simple technique.
It is based on building p2p communication channels between L3 routers using STP ( or more precisely RSTP ) and disabling the storage of MAC addresses on intermediate switches.
The advantage of this solution is that the time for determining the malfunction and the time for restoring work are determined by the level 3 routing protocol used and are independent of the convergence time of the STP protocol.
About STP it is written much enough, for example on Habré , I will not describe the details.
To reserve communication channels between routers, you can use the appropriate dynamic routing protocols.
- On routers on two parallel logical links, the appropriate dynamic routing protocols are configured (do not forget to specify the type of link p2p, if necessary;)).
- For switches of each of the two parallel p2p-channels (VLANs), an STP-free tree is built up. The topology of each VLAN should be built in such a way that in case of failure of any of the network components between the two end routers, the second p2p channel continues to work.
- On all intermediate switches, for VLANs involved in the organization of p2p links, you can disable MAC address memorization. This allows you to simplify the requirements for the parameters of intermediate switches when the traffic of a large number of devices with unique MAC addresses passes through them.
An example of use in real life is here.
PS You can try to do without STP, using only the manipulation of the VLAN ID on the interfaces. But, in case of an error (when planning, implementing or making changes), the network will no longer work correctly.
UPD: Added a few explanations, without pictures (before NG, there is no time, alas). Perhaps later will make an update).