Notas estudo JNCIS-ENT parte 2

Nota: Este Post faz parte do guide de Switching.

Spanning-tree

IEEE 802.1D

Bridge ID – Identificador unico para cada switch
Root Bridge – Switch  com o lowest bridge ID
Root port –
Root path cost –
Port cost – valor configuravel 1-200000000 (default 20000 para 1Gb)
Designated bridge –
Port ID –
Designated port – porta designada para enviar trafego na diracao root->LAN ou vice-versa
Bridge protocol data unit (BPDUs) – Info sobre configuration BPDU e Topology change notification BPDU

BPDU Type:  contem – configuration BPDU (0x00) ou TCN BPDU (0x80).

STP Port States

Blocking – Listen BPDUs
Listening – Listen BPDUs
Learning – Listen BPDUs + MAC learning
Forwarding – Listen/Send BPDUs + MAC learning

Reconvergence STP

sw1-sw2-sw3-sw4(root)

sw1 link down
sw2 envia pela root port um TCN e recebe um TCN ACK do sw3
sw3 envia pela root port um TCN e recebe um TCN ACK do sw4(root)
sw4 envia um TC flag (configuration BPDU) para todos os non-root switchs, este fazem flush (aging) usando o forwarding delay time (default 15 seconds)

Drawbacks STP

Reconvergence entre 30 a 50 segundos (20s age out + 30s listening+learning)

RSTP force version 0 é compatível com o STP

RSTP

IEEE 802.1w

Improvements

Direct e indirect link failure and recovery
Point-to-Point

New port roles:

Alternate port – Backup root port, block traffic enquanto receber um BPDUs superiores
Backup port – Redundant path para um segmento (apenas nos designated switches)

Port States:

Discarding (Alternate,Disabled ports) – mesmo que o Blocking|Listening
Learning – Learning
Forwarding (Root and Designated ports) – Forwarding

Protocol Version – 0x02
BPDU Type – 0x02 (RST BPDU)

Topology Changes

As transições para o discarding state não despoletam STP TCN/TCN ACK
Os RSTP TCNs (com TCN Flag set) são enviados por todas as portas (root/designated ports)
Apos receber o RSTP TCN o switch:

• switches nao faz flush dos MAC learned das edge ports
• switches nao faz flush dos MAC learned das portas onde recebeu o TCN

Configuring STP

edit protocols rstp
!Parametros default
set bridge-priority 32k
set max-age 20
set hello-time 2
set forwarding-delay 15

lab@exC-1# run show spanning-tree bridge

STP bridge parameters
Context ID                          : 0
Enabled protocol                    : STP
Root ID                           : 0.88:e0:f3:6f:37:80
Root cost                         : 39000
Root port                         : ge-0/0/14.0
Hello time                        : 2 seconds
Maximum age                       : 20 seconds
Forward delay                     : 15 seconds
Message age                       : 3
Number of topology changes        : 3
Time since last topology change   : 5 seconds
Topology change initiator         : ge-0/0/14.0
Topology change last recvd. from  : b0:c6:9a:de:26:90
Local parameters
Bridge ID                       : 32768.2c:6b:f5:33:40:81
Extended system ID              : 0
Internal instance ID            : 0

!Desativar STP numa interface
set protocols stp interface ge-0/0/10.0 disable

set protocols stp interface ge-0/0/13.0 cost 2000 mode point-to-point

set protocols stp interface ge-0/0/14.0 priority 128 mode shared

set protocols stp interface ge-0/0/2.0 edge

lab@Switch-1# run show spanning-tree interface

Spanning tree interface parameters for instance 0

Interface    Port ID    Designated      Designated         Port    State  Role
port ID        bridge ID          Cost
ge-0/0/6.0     128:519      128:519  32768.2c6bf5334081     20000  FWD    DESG
ge-0/0/13.0    128:526      128:526  32768.2c6bf5334081      2000  FWD    DESG
ge-0/0/14.0    128:527      128:641  32768.b0c69ade2680     20000  FWD    ROOT

Referências:

Notas estudo JNCIS-ENT parte 1