{"id":840,"date":"2021-08-20T03:08:35","date_gmt":"2021-08-20T03:08:35","guid":{"rendered":"http:\/\/feralpacket.org\/?p=840"},"modified":"2021-08-20T03:08:35","modified_gmt":"2021-08-20T03:08:35","slug":"multiple-spanning-tree-mst-notes","status":"publish","type":"post","link":"https:\/\/feralpacket.org\/?p=840","title":{"rendered":"Multiple Spanning Tree (MST) Notes"},"content":{"rendered":"

Multiple Spanning Tree (MST)<\/span><\/p>\n

 – 802.1S<\/p>\n

 – Called MSTP by Cisco previously<\/p>\n

 – Can map VLANs to STP instances<\/p>\n

     -> e.g. – <\/p>\n

          -> Instance 1<\/p>\n

               -> VLAN 1 – 32<\/p>\n

          -> Instance 2<\/p>\n

               -> VLAN 33 – 65<\/p>\n

          -> Instance 3<\/p>\n

               -> VLAN 66 – 100<\/p>\n

 – Only supports RSTP for convergence<\/p>\n

     -> Activated automatically<\/p>\n

 – Problem<\/p>\n

     -> Every switch needs to be configured the same<\/p>\n

          -> Manually<\/p>\n

     -> VTP cannot be used<\/p>\n

     -> Use notepad<\/p>\n

 – MST creates a set of switches using the same configuration<\/p>\n

     -> Called a Region<\/p>\n

     -> All have the exact same configuration<\/p>\n

     -> Allows up to 16 instances per Region<\/p>\n

          -> Instance 0 – 15<\/p>\n

          -> Instance 0<\/p>\n

               -> Internal Spanning Tree (IST)<\/p>\n

               -> By default, all VLANs map to IST<\/p>\n

 – Every MST configuration has 3 variables<\/p>\n

     -> Region name<\/p>\n

          -> Default is NULL<\/p>\n

     -> Revision number<\/p>\n

          -> Default is 0<\/p>\n

     -> Instance to VLAN mapping<\/p>\n

          -> Default, all VLANs map to IST<\/p>\n

 – Configure one switch, then copy that configuration to all other switches<\/p>\n

 – Can configure all of the MST parameters, then activate MST<\/p>\n

 – Only one BPDU is sent<\/p>\n

     -> Controlled by the IST<\/p>\n

     -> Specific information about instances attaches as \u201cM-Records”<\/p>\n

<\/p>\n

SW1(config)# spanning-tree mst configuration<\/span><\/p>\n

SW1(config-mst)# name CISCO<\/span><\/p>\n

 revision 10<\/span><\/p>\n

 instance 1 vlan 1 – 32<\/span><\/p>\n

 instance 2 vlan 33 – 65<\/span><\/p>\n

 instance 3 vlan 66 – 100<\/span><\/p>\n

 show pending<\/span><\/p>\n

 exit<\/span><\/p>\n

SW1(config)# spanning-tree mode mst<\/span><\/p>\n

Scenario -> In instance 0, configure all VLANs except VLANs 1 – 100.<\/p>\n

 – If the question asks you to configure all other VLANs to one instance (after first two), only configure two instances.<\/p>\n

     -> All other VLANs will be in instance 0<\/p>\n

show spanning-tree mst configuration<\/span><\/p>\n

show spanning-tree mst [id]<\/span><\/p>\n

MST introduces MAX HOPS feature<\/span><\/p>\n

 – Allows equal to MAX-AGE time<\/p>\n

 – Change MAX-AGE time to configure the maximum hops<\/p>\n

MST Interface Costs<\/span><\/p>\n

 – 10 Mbps \u2014> 2000000<\/p>\n

 – 100 Mbps \u2014> 200000<\/p>\n

 – 1 Gbps \u2014> 20000<\/p>\n

 – 10 Gbps \u2014> 2000<\/p>\n

SW1(config)# spanning-tree mst 1 priority 4096<\/span><\/p>\n

     – or –<\/p>\n

SW1(config)# spanning-tree mst 1 root primary<\/span><\/p>\n

     – or –<\/p>\n

SW1(config)# spanning-tree mst 1 root secondary<\/span><\/p>\n

Can configure who will be the root for IST (instance 0)<\/p>\n

<\/p>\n

Only the IST communicates between Regions<\/p>\n

 – Sends a single BPDU<\/p>\n

     -> Removes M-Records<\/p>\n

          -> This hides the topology of the Region<\/p>\n

          -> Similar to the ABR in OSPF<\/p>\n

 – One Region appears as a single switch to another Region<\/p>\n

<\/p>\n

CIST Root<\/span><\/p>\n

 – The best Bridge-ID switch among all Regions<\/p>\n

Region Root<\/span><\/p>\n

 – Instance 0 root bridge in every Region<\/p>\n

 – In any Region, only a boundary switch can be a Region root<\/p>\n

     -> Exception, the CIST root is also the Region root and does not have to be a boundary switch<\/p>\n

     1.  Root bridge<\/p>\n

     2.  Cost to reach root bridge (CIST)<\/p>\n

          -> Internal cost within the Region are not considered to determine the Region root<\/p>\n

          -> Only external cost is considered<\/p>\n

     3.  Sender Bridge-ID<\/p>\n

     4.  Sender Port-ID<\/p>\n

<\/p>\n

Master Port<\/span><\/p>\n

 – Root port of any Region<\/p>\n

 – On Region root<\/p>\n

 – Seen as \u201cmaster port\u201d by non-IST instances<\/p>\n

     -> Going toward the master<\/p>\n

show spanning-tree mst 0<\/span><\/p>\n

 – Shows the root port<\/p>\n

show spanning-tree mst 1<\/span><\/p>\n

 – Show the master port<\/p>\n

<\/p>\n

show run | in mst|name|rev|ins<\/span><\/p>\n

show spanning-tree mst configuration<\/span><\/p>\n

 – Should be the same as<\/p>\n

     -> show pending<\/span><\/p>\n

show spanning-tree mst<\/span><\/p>\n

clear spanning-tree detected-protocols<\/span><\/p>\n

 – To switch to MST faster<\/p>\n

<\/p>\n

SW1(config)# spanning-tree mode pvst+<\/span><\/p>\n

no spanning-tree mst configuration<\/span><\/p>\n

<paste MST configuration from Notepad><\/p>\n

 show pending<\/span><\/p>\n

 exit<\/span><\/p>\n

spanning-tree mode mst<\/span><\/p>\n

SW2# show spanning-tree mst<\/span><\/p>\n

 E3\/0     Root     FWD     Shr Bound (RSTP)<\/p>\n

SW3# show spanning-tree mst<\/span><\/p>\n

 E3\/0     Altn     BLK     Shr Bound (RSTP)<\/p>\n

 E3\/1     Altn     BLK     Shr Bound (RSTP)<\/p>\n

SW2# show spanning-tree mst 1<\/span><\/p>\n

 E3\/0     Mstr     FWD     Shr Bound (RSTP)<\/p>\n","protected":false},"excerpt":{"rendered":"

Multiple Spanning Tree (MST)<\/p>\n","protected":false},"author":1,"featured_media":834,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[31,61,15],"class_list":["post-840","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\/840","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=840"}],"version-history":[{"count":1,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/840\/revisions"}],"predecessor-version":[{"id":970,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/posts\/840\/revisions\/970"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=\/wp\/v2\/media\/834"}],"wp:attachment":[{"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=840"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=840"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/feralpacket.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=840"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}