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Beginner

STP

Please can someone tell me meaning of each line.

Port 257 (GigabitEthernet3/1) of VLAN0102 is designated forwarding
Port path cost 4, Port priority 128, Port Identifier 128.257.
Designated root has priority 4198, address d0c7.89a9.c940
Designated bridge has priority 4198, address d0c7.89a9.c940
Designated port id is 128.257, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 427353, received 3

122 REPLIES 122
Hall of Fame Expert

Hello Jain,

Hello Jain,

the output is taken from show spanning-tree gi3/1 detail.

The section of output applies to Vlan 102.

Port 257 (GigabitEthernet3/1) of VLAN0102 is designated forwarding

257 is the SNMP ifindex of interface gi3/1 is an internal identity of the port. The port is in Designated Forwarding state means it is in forwarding state for STP for instance running in Vlan102 because the port has been elected as the Designated port in the segment.

Port path cost 4, Port priority 128, Port Identifier 128.257

The STP cost of a GE port is 4 with short metric, the port priority is a priority assigned to the port 128 is the default value. The port identifier is the result of putting together  port priority and port ID (SNMP ifindex 257 see above).

Designated root has priority 4198, address d0c7.89a9.c940

the root bridge for Vlan102 STP instance has bridge priority 4198 = 4096+102, the switch is using extended system-id also known as MAC address reduction. the root bridge MAC address is d0c7.89a9.c940

Designated bridge has priority 4198, address d0c7.89a9.c940

the bridge-id of the Designated bridge for the segment pleaese note is the same as the line before, this means the local switch is the root bridge for Vlan 102

Designated port id is 128.257, designated path cost 0

the designated port for the segment is gi3/1 that is identified by 128.257 priority.SNMP ifindex.

the designated path cost is 0 because this switch is indeed the root bridge so the accumulated cost to the root bridge is 0.

Timers: message age 0, forward delay 0, hold 0

>> this is not clear to me I would expect values different from 0, but it may be related to the Rapid STP type running on the switch.

Number of transitions to forwarding state: 1

the port transitioned to STP fowarding state only one time

Link type is point-to-point by default

this may indicate the switch is running Rapid PVST and not PVST+ as the point-to-point link concept has been introduced with Rapid STP.

BPDU: sent 427353, received 3

except 3 BPDUs received  this port is sending out regularly STP BPDUs for STP instance in vlan102.

Hope to help

Giuseppe

Beginner

Thanks for your reply. Please

Thanks for your reply. Please tell me also.

257 is the SNMP ifindex of interface gi3/1

how 257 value is calculated or by default because i see 358 398 also. how these value are coming 

Hall of Fame Expert

Hello Jain,

Hello Jain,

as far as I know SNMP ifindex is calculated at boot time and each interface should get a value.

In some platforms there is a feature called SNMP ifindex persist that allows to use the same values across reloads but it is not guaranteed when performing updates.

The problem of SNMP ifindex consistency involves SNMP gets from management systems NME and also other features like Netflow that use the ifindex to describe the interface.

In any case, you cannot assign the SNMP ifindex you can only achieve persistency across reloads with appropriate commands on supported platforms.

Hope to help

Giuseppe

Beginner

ok , suppose in my network

ok , suppose in my network there is looping in that case what i check to solve this problem..

VIP Mentor

this command helps trace a

this command helps trace a loop , start at core and follow the constant most recent occurring changes

show spanning-tree detail | inc ieee|occurr|from|is exec

Beginner

what i will get here.... i

what i will get here.... i mean after putting this command what i need to follow...

VIP Mentor

so example from switch below

so example from switch below of the output , shows a change occurred 17 mins  coming from port g2/0/10 , then I would do a show cdp neighbour see whats connected to that poort , jump onto the switch connected and run the command again , STP changes should not be occurring frequently so there usually easy enough to follow , this will eventually bring you to the port that may be causing it , whether its faulty , lose cable or bad device attached

VLAN0001 is executing the ieee compatible Spanning Tree protocol
  Number of topology changes 5674 last change occurred 17:35:34 ago
          from GigabitEthernet2/0/10

Beginner

Thank you mark/Giuseppe

Thank you mark/Giuseppe

Please can you tell me also about MPLS basic configuration how to apply when to apply and where to apply 

VIP Mentor

Yes I know MPLS you only

Yes I know MPLS you only configure that if your an ISP provider like BT or AT & T really

Its all service provider how they switch there customer traffic across their networks and what they use to do it at layer 2

If your not an ISP you should only really be configuring BGP on your CE customer edge equipment and not even see MPLS

MPLS is a service you buy from the ISP rather than using the internet they dedicate your traffic across their global networks

Beginner

Please mark can you help me

Please mark can you help me actually in interview they ask about MPLS , what i say can you tell me more so i can clear interview. it will be help for me. 

i have knowledge in BGP but what i say when they ask about MPLS 

can you share some more information like

configuration 

VIP Mentor

There's no point me just

There's no point me just stating config if its an interview they will catch you out straight away like that  , this video below is clear and easy to understand you should try learn it you will come across a lot better

https://www.youtube.com/watch?v=--IHeAdipHk

Beginner

ok , can i ask some more

ok , can i ask some more question about HSRP if you don mind...

VIP Mentor

yes go for it

yes go for it

Beginner

Suppose on one core switch 

Suppose on one core switch 

SW1# int vlan 100

standby 11 ip 10.1.100.1
standby 11 priority 110
standby 11 preempt

on second switch 

SW2# int vlan 100

standby 11 ip 10.1.100.1
standby 11 preempt

suppose here sw1 down ok , by default it will decrese self value from 110 to 100 ok , how will sw2 become active because
sw2 also have 100 by defualt.

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