![\"\"](\"https:\/\/www.spktechfit.com\/wp-content\/uploads\/2024\/05\/5.1.png\")
<\/p>\n<\/p>\n
In the above example on the left, if Core 1 fails then the network is down and client A won’t be able to communicate with client B.<\/p>\n
In the example on the right, if Core 1 fails the network will say up as Core 2 is available and the Client can communicate through this.<\/p>\n
While this mitigates a single point of failure issue it creates a new challenge – Loops.<\/p>\n
<\/p>\n
![\"\"](\"https:\/\/www.spktechfit.com\/wp-content\/uploads\/2024\/05\/5.2.png\")
<\/p>\n
Redundant links create L2 loops which can cause major problems.<\/p>\n
Broadcast Storms<\/strong><\/p>\n <\/p>\n If the switch receives a unicast packet to some destination MAC and that address has not yet been learned in the MAC address table, then the switch floods the frame out all ports in the VLAN except the ingress port. These can also circulate and waste bandwidth and CPU cycles, plus cause tother issues.<\/p>\n <\/p>\n The IEEE 802.1d standard version of STP was developed to build and maintain redundant, yet loop free networks. STP creates a loop free topology by automatically disabling redundant links. However, these links disabled links remain available to provide redundancy in the case of a failure.<\/p>\n One switch in the Spanning Tree domain is elected as the bridge or Root switch. The root bridge is the reference from which the spanning Tree grows. All other switches are non-root bridges, sometimes known as designated switches.<\/p>\n When discussing STP the terms switch and bridge are used to describe the same thing<\/span><\/p>\n In the original standard only the root switch sent hello packets every 2 seconds. These were forwarded on to the rest of the switches in the domain. If a switch didn\u2019t receive a hello packet for 20 seconds (the default MAX age timer) an outage was assumed and the switches converged to a new topology.<\/p>\n Rapid Spanning-Tree Protocol (RSTP) was developed in 1998 to speed up convergence. In RSTP all switches send Hello packets. The need for Max Age timers is eliminated.<\/p>\n <\/p>\n Spanning Tree assigns each switch a unique identifier called a Bridge ID. This is composed of a 2-byte priority and 6-byte MAC address. The default priority is 32768. By default each switch has the same priority, but each switch has a unique MAC address so the Bridge ID is unique.<\/p>\n All switches in the Spanning Tree domain exchange control messages called Bridge Protocol Data Units (BPDUs). In the original STP only the root switch sent them.<\/p>\n In RSTP all switches send BPDU’s with their current information every 2 seconds, the default hello time period. If a port doesn\u2019t receive BPDUs for three consecutive hello timers, the switch quickly knows it has lost connectivity to the neighbour and begins to converge. Because each switch sends BPDUs it is a truly keepalive mechanism. Failure detection takes no longer than 6 seconds.<\/p>\n During Spanning Tree establishment, and any ensuing convergence, switches must decide which ports will forward data and which ports must be disabled to prevent L2 loops.<\/p>\n The table below lists the states were used in the original STP (802.1d) and the RSTP (802.1w) and compares them<\/p>\n In RSTP the Leaning state is a transition state and is only used during re-convergence of the protocol when change happens. Stable states are the Discarding or Forwarding states.<\/p>\n RSTP may have several possible paths to get from route switch to a particular non-root switch. It chooses the best path based on coast, which is based on link speed.<\/p>\n Designated Port:<\/span><\/p>\n Root Port:<\/span><\/p>\n Alternate port:<\/span><\/p>\n Backup port:<\/span><\/p>\n <\/p>\n RSTP algorithm creates a loop free network by the following steps:<\/p>\n All other ports move to a blocking state to prevent loops<\/span><\/p>\n This is based on the Bridge ID (BID) which is made up of a priority number (default is 32,768 but you can set it yourself) and the switch MAC address. The switch with the lowest BID wins.<\/p>\n The priority must be configured in increments of 4096. In the example table below you can see Core 1 has the value of 4096 and Core 2 8192<\/p>\n Non root switches must select the best path to the root switch by selecting its root port. Root port criteria are as follows:<\/p>\n In the diagram above, Core-2 receives BPDUs on ports 1,2,43 and 44. Core 2 must decide which port is the Root port.<\/p>\n The criteria to select a Designated port is the same as the Root port.<\/p>\n Edge Ports connect to endpoints and do not receive BPDUs. This means they don\u2019t need to be part of the Spanning Tree algorithm and can therefore quickly transition to the forwarding state with no intermediate steps.\u00a0If BPDUs are received on an edge port, then the port will act as a normal Spanning Tree port and participate in the algorithm. You must manually configure Edge ports.<\/p>\n Switch(config)#interface 1\/1\/1 An alternative to the admin-edge option is the AOS-CX administrative-network option. With this option\u00a0 the port looks for BPDUs for the first 3 seconds after the link is up, if non are received the port becomes an edge port and immediately forwards frames. If BPDUs are detected it becomes non-edge port and participates in normal STP operation.<\/p>\n Switch(config)#interface 1\/1\/1 In RSTP a topology change occurs when non-edge port move to a different state or BPDUs are no longer received.<\/p>\n Topology change process:<\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" Redundancy In the above example on the left, if Core 1 fails then the network is down and client A won’t be able to communicate with client B. In the example on the right, if Core 1 fails the network will say up as Core 2 is available and the Client can communicate through this. […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[17,3],"tags":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.spktechfit.com\/index.php?rest_route=\/wp\/v2\/posts\/892"}],"collection":[{"href":"https:\/\/www.spktechfit.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.spktechfit.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.spktechfit.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.spktechfit.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=892"}],"version-history":[{"count":2,"href":"https:\/\/www.spktechfit.com\/index.php?rest_route=\/wp\/v2\/posts\/892\/revisions"}],"predecessor-version":[{"id":1001,"href":"https:\/\/www.spktechfit.com\/index.php?rest_route=\/wp\/v2\/posts\/892\/revisions\/1001"}],"wp:attachment":[{"href":"https:\/\/www.spktechfit.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=892"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.spktechfit.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=892"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.spktechfit.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=892"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/www.spktechfit.com\/wp-content\/uploads\/2024\/05\/5.3.png\")
<\/p>\n\n
Multiple Frame Copies<\/h3>\n
![\"\"](\"https:\/\/www.spktechfit.com\/wp-content\/uploads\/2024\/05\/5.4.png\")
<\/p>\n\n
Spanning-Tree Protocol (STP)<\/h3>\n
![\"\"](\"https:\/\/www.spktechfit.com\/wp-content\/uploads\/2024\/05\/5.5.png\")
<\/p>\n![\"\"](\"https:\/\/www.spktechfit.com\/wp-content\/uploads\/2024\/05\/5.6.png\")
<\/p>\n![\"\"](\"https:\/\/www.spktechfit.com\/wp-content\/uploads\/2024\/05\/5.7.png\")
<\/p>\nRSTP elements<\/h3>\n
Bridge Identifier<\/h4>\n
Bridge Protocol Data Units<\/h3>\n
Port States<\/h3>\n
![\"\"](\"https:\/\/www.spktechfit.com\/wp-content\/uploads\/2024\/05\/5.8.png\")
<\/p>\nPath Cost<\/h3>\n
![\"\"](\"https:\/\/www.spktechfit.com\/wp-content\/uploads\/2024\/05\/5.9.png\")
<\/p>\nPort Roles<\/h3>\n
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RSTP Operation<\/h3>\n
Operational Overview<\/h2>\n
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![\"\"](\"https:\/\/www.spktechfit.com\/wp-content\/uploads\/2024\/05\/5.10.png\")
<\/p>\n\n
\n
![\"\"](\"https:\/\/www.spktechfit.com\/wp-content\/uploads\/2024\/05\/5.11.png\")
<\/p>\n\n
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<\/h3>\n
Edge Ports<\/h3>\n
\n<\/i>Switch(config-if)# spanning-tree port-type admin-edge<\/i><\/p>\n
\n<\/i>Switch(config-if)# spanning-tree port-type admin-network<\/i><\/p>\nTopology Change Mechanism<\/h3>\n
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![\"\"](\"https:\/\/www.spktechfit.com\/wp-content\/uploads\/2024\/05\/5.12.png\")
<\/p>\n