{"id":824,"date":"2021-08-20T03:09:34","date_gmt":"2021-08-20T03:09:34","guid":{"rendered":"http:\/\/feralpacket.org\/?p=824"},"modified":"2021-08-20T03:09:34","modified_gmt":"2021-08-20T03:09:34","slug":"spanning-tree-protocol-stp-notes","status":"publish","type":"post","link":"https:\/\/feralpacket.org\/?p=824","title":{"rendered":"Spanning Tree Protocol (STP) Notes"},"content":{"rendered":"

Spanning Tree Protocol (STP)<\/span><\/p>\n

 – 802.1D<\/p>\n

 – Used to prevent loops while maintaining redundancy<\/p>\n

<\/p>\n

1.  Reference Point<\/span><\/p>\n

 – Root Bridge<\/p>\n

     -> Priority<\/p>\n

          -> Lower is better<\/p>\n

     -> Base MAC address<\/p>\n

          -> Lower is better<\/p>\n

 – Priority<\/p>\n

     -> 0 – 61440<\/p>\n

          -> Default is 32768<\/p>\n

2.  Hello messages sent every 2 seconds to other switches<\/span><\/p>\n

 – Bridge Protocol Data Unit (BPDU)<\/p>\n

     -> Information about the root bridge<\/p>\n

          -> Bridge-ID<\/p>\n

          -> Timers<\/p>\n

     -> Cost to reach the root bridge<\/p>\n

3.  Cost is a property of the interface<\/span><\/p>\n

 – 10 Mbps<\/p>\n

     -> 100<\/p>\n

 – 100 Mbps<\/p>\n

     -> 19<\/p>\n

 – 1 Gbps<\/p>\n

     -> 4<\/p>\n

 – 10 Gbps<\/p>\n

     -> 2<\/p>\n

4.  Port-id is a property of the interface<\/span><\/p>\n

 – Port-priority + Interface-id<\/p>\n

 – Port-priority<\/p>\n

     -> 8 bit variable<\/p>\n

     -> 0 – 240<\/p>\n

     -> Default is 128<\/p>\n

     -> Changed in intervals of 16<\/p>\n

     -> Lower is better<\/p>\n

 – Interface-id<\/p>\n

     -> fa0\/5 == 5 (generally\u2026)<\/p>\n

     -> Different on switch stacks<\/p>\n

5.  Cost is incremented on every incoming port<\/span><\/p>\n

6.  By default, the root bridge sends BPDU cost of 0<\/span><\/p>\n

7.  Port Roles<\/span><\/p>\n

 – Root port<\/p>\n

     -> Upstream port having least cost route (path) towards the root bridge<\/p>\n

     -> Forwarding port<\/p>\n

     -> Does not send BPDUs<\/p>\n

 – Designated port<\/p>\n

     -> Downstream port, going further away from the root bridge<\/p>\n

     -> Forwarding port<\/p>\n

     -> Sends BDPUs<\/p>\n

 – Non-Designated port<\/p>\n

     -> Downstream port, but least desirable on a network segment<\/p>\n

     -> Blocking port<\/p>\n

     -> Still processes BPDUs<\/p>\n

8.  Any port remaining after root port is selected is considered designated port by the switch<\/span><\/p>\n

9.  If more than one designated port is on the same segment, only one can remain the designated port<\/span><\/p>\n

 – Decided by STP Conflict Resolution Procedure (CRP)<\/span><\/p>\n

     1.  Root Bridge ID<\/p>\n

     2.  Least cost towards root bridge<\/p>\n

     3.  Sender Bridge-ID is compared with local Bridge-ID<\/p>\n

     4.  Sender\u2019s Port-ID is compared<\/p>\n

          -> Used when multiple ports are connected to the same switch<\/p>\n

<\/p>\n

STP Reconvergence (1st Scenario)<\/span><\/p>\n

 – Direct link failure<\/p>\n

     1.  Listening state<\/p>\n

          -> 15 seconds (forwarding delay)<\/p>\n

     2.  Learning state<\/p>\n

          -> 15 seconds (forwarding delay)<\/p>\n

     3.  Forwarding state<\/p>\n

          -> After 30 seconds<\/p>\n

STP Reconvergence (2nd Scenario)<\/span><\/p>\n

 – Indirect link failure<\/p>\n

 – Link between SW1 & SW3 goes down<\/p>\n

     -> SW3 sends BPDUs to SW5 claiming to be the root bridge<\/p>\n

     1.  MAX AGE time<\/p>\n

          -> 20 seconds<\/p>\n

     2.  Listening state<\/p>\n

          -> 15 seconds (forwarding delay)<\/p>\n

     3.  Learning state<\/p>\n

          -> 15 seconds (forwarding delay)<\/p>\n

     4.  Forwarding state<\/p>\n

          -> After 50 seconds<\/p>\n","protected":false},"excerpt":{"rendered":"

Spanning Tree Protocol (STP)<\/p>\n","protected":false},"author":1,"featured_media":822,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[31,61,15],"class_list":["post-824","post","type-post","status-publish","format-standard","hentry","category-ccie","tag-published","tag-spanning-tree","tag-stp"],"_links":{"self":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/824","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=824"}],"version-history":[{"count":1,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/824\/revisions"}],"predecessor-version":[{"id":975,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/824\/revisions\/975"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/media\/822"}],"wp:attachment":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=824"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=824"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=824"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}