08-06-2006 05:49 AM - edited 03-03-2019 01:34 PM
Hi All,
I would like to know 2 things related to Span-tree, as we deployed it on our switches:
1- what is spantree priority? and when should I higher or lower the priority?
also what is the default priority?
2- what is spantree cost? and when should I lower or higher the spantree cost on an interface? what is the default spantree cost for a vlan?
Please let me know your feedback since I have lots of doubts about spantree & BPDU?
Appreciate your Help..
08-06-2006 08:26 AM
Hi,
1) Priority is used to elect root bridge; brdigeID=2byte (Priority)+ 6byte (MAC). Default is 32768, the lower value is more prefered in the root bridge election. If there is tie in priority the lower MAC address is prefered.
2) Cost is a kind of distance from the root bridge, cost is depend on the port speed: 10G -> 2; 1G ->4; 100M ->19; 10M ->100..., with cost you can control on which switch which port become designated port for the segment...
bye
FCS
Please rate me if I helped
08-07-2006 02:07 AM
Hi FCS,
I just have one question to clarify 2 things:
What is the root ID & the Bridge ID??
Is it the port ID it self on the swith or the Switch ID??
FOR example: the bellow is an output from one of our backbone switches:
Omam# sh span tree vlan 805
MST07
Spanning tree enabled protocol mstp
Root ID Priority 32775
Address 0015.c6c0.8800
Cost 60000
Port 20 (GigabitEthernet0/20)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32775 (priority 32768 sys-id-ext 7)
Address 0016.c70d.7880
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- ---------------------------
Gi0/1 Boun FWD 200000 128.1 P2p Bound(PVST)
Gi0/3 Boun FWD 200000 128.3 P2p Bound(PVST)
Gi0/4 Desg FWD 200000 128.4 P2p
Gi0/19 Boun FWD 200000 128.19 P2p Bound(PVST)
Gi0/20 Root FWD 20000 128.20 P2p
Po1 Altn BLK 100000 128.616 P2p
Appreciate your feedback,
08-07-2006 02:13 AM
Root Bridge is a switch who wins the root election in SPT, it has the best RootBridgeID (best means lowest). RootBridegID is 8bytes ID, include 2 bytes prioriry and 6 byes MAC address.
This is your RootBridgeID:
Root ID Priority 32775 + Address 0015.c6c0.8800
bye
FCS
Please rate me if I helped.
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide