Download als PDF FileSpanning-tree Portfast ist auch eins der Features das sicherlich jeder kennt. Im wesentlichen überspringt es beim hochnehmen eines Ports die Listening (15s) und Learning (15s) Phase und geht direkt in den Forward (oder blocking!) mode.
Ohne Portfast:
CAT2(config)#int fa0/12 CAT2(config-if)#no spanning-tree portfast CAT2(config-if)#shut CAT2(config-if)# *Apr 20 22:56:43.690: %LINK-5-CHANGED: Interface FastEthernet0/12, changed state to administratively down *Apr 20 22:56:44.697: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/12, changed state to down CAT2(config-if)#do sh span int fa0/12 no spanning tree info available for FastEthernet0/12 CAT2(config-if)#no shut CAT2(config-if)#UPDOWN: Interface FastEthernet0/12, changed state to up *Apr 20 22:57:27.303: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/12, changed state to up CAT2(config-if)#do sh span int fa0/12 Vlan Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- -------------------------------- VLAN0005 Desg LIS 19 128.14 P2p CAT2(config-if)# CAT2(config-if)#do sh span int fa0/12 Vlan Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- -------------------------------- VLAN0005 Desg LRN 19 128.14 P2p CAT2(config-if)#do sh span int fa0/12 Vlan Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- -------------------------------- VLAN0005 Desg FWD 19 128.14 P2p
Mit Portfast:
CAT2(config-if)#spanning-tree portfast
CAT2(config-if)#shut
CAT2(config-if)#no shut
*Apr 20 23:01:39.196: %LINK-3-UPDOWN: Interface FastEthernet0/20 23:01:40.202: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/12, changed state to down
CAT2(config-if)#do sh span int fa0/12
*Apr 20 23:01:43.021: %LINK-3-UPDOWN: Interface FastEthernet0/12, changed state to up
*Apr 20 23:01:44.028: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/12, changed state to up
CAT2(config-if)#do sh span int fa0/12
Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0005 Desg FWD 19 128.14 P2p Edge
Global aktivieren:
CAT2(config)#spanning-tree portfast default ? <cr> CAT2(config)#spanning-tree portfast default %Warning: this command enables portfast by default on all interfaces. You should now disable portfast explicitly on switched ports leading to hubs, switches and bridges as they may create temporary bridging loops.
Pro Port aktivieren:
CAT2(config)#int fa0/9 CAT2(config-if)#spanning-tree portfast %Warning: portfast should only be enabled on ports connected to a single host. Connecting hubs, concentrators, switches, bridges, etc... to this interface when portfast is enabled, can cause temporary bridging loops. Use with CAUTION %Portfast has been configured on FastEtherne when the interface is in a non-trunking mode. CAT2(config-if)#
Was ist zu beachten:
- Sollte nur auf Accessports aktiviert werden
- Kann temporär Loops verursachen
- Sollte im Zusammenhang mit BPDU Guard auf Accessports konfiguriert werden
Beispiel eines temporären Loops:
CAT2(config-if)#no shut *Apr 20 23:07:05.806: %LINK-3-UPDOWN: Interface FastEthernet0/23 %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/23, changed state to up *Apr 20 23:07:08.675: %SPANTREE-2-BLOCK_BPDUGUAR CAT2#D: Received BPDU on port Fa0/23 with BPDU Guard enabled. Disabling port. *Apr 20 23:07:08.675: %PM-4-ERR_DISABLE: bpduguard error detected on Fa0/23, putting Fa0/23 in err-disable state CAT2# *Apr 20 23:07:09.707: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/23, changed state to down
Obwohl der Port sofort auf err-disabled geht. Gibt es aus der Sicht von CAT3 kurzzeitig einen Loop:
CAT3(config-if)# *Apr 20 22:43:01.967: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f001 in vlan 11 is flapping between port Fa0/22 and port Fa0/20 *Apr 20 22:43:02.337: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f001 in vlan 15 is flapping between port Fa0/22 and port Fa0/20 *Apr 20 22:43:02.337: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f002 in vlan 12 is flapping between port Fa0/22 and port Fa0/20 *Apr 20 22:43:02.404: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f001 in vlan 13 is flapping between port Fa0/22 and port Fa0/2 CAT3(config-if)#0 *Apr 20 22:43:02.471: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f002 in vlan 14 is flapping between port Fa0/22 and port Fa0/20 *Apr 20 22:43:02.538: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f002 in vlan 16 is flapping between port Fa0/22 and port Fa0/20 CAT3(config-if)# *Apr 20 22:43:07.068: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f002 in vlan 16 is flapping between port Fa0/22 and port Fa0/20 *Apr 20 22:43:07.068: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f001 in vlan 15 is flapping between port Fa0/20 and port Fa0/22 *Apr 20 22:43:07.101: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f001 in vlan 13 is flapping between port Fa0/22 and port Fa0/20 *Apr 20 22:43:07.168: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f001 in vlan 11 is flapping between port Fa0/22 and port Fa0/2 CAT3(config-if)#0 *Apr 20 22:43:07.168: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f002 in vlan 14 is flapping between port Fa0/20 and port Fa0/22 *Apr 20 22:43:07.269: %SW_MATM-4-MACFLAP_NOTIF: Host 0000.0c9f.f002 in vlan 12 is flapping between port Fa0/22 and port Fa0/20 CAT3(config-if)#
Arbeitet in Raum Basel (Switzerland) als Senior Network Engineer mit über 15 Jahren Erfahrung im Bereich Netzwerk