园区网多层架构和设计指南——思科.ppt

F2 F2 event #2 holepp#1far fic HSo R ed ? Backbonetil fast limits A P G Un cti Active s v oe HSRPtime (30 seconds) to 64 ? 2005 Cisco Systems, Inc. All rights reserved. Cisco Confidential RST-2032 PVST+ at least one second before event #2 如果分布层没有互连 黑洞和多次 ‘转换’… ? Blocking link on access-b will take 50 seconds to move to forwarding traffic black hole until HSRP goes active on standby HSRP peer ? After MaxAge expires (or backbone fast or Rapid PVST+) converges HSRP preempt causes another transition ? Access-b used as transit for access-a’s traffic F 2 MaxAge Seconds Before Failure Is Detected….Then Listening and Learning F: Forwarding B: Blocking Access-b VLAN 2 STP Root and HSRP Active Si Core Hellos ? Aggressive HSRP STP timers limit black Secondary Dr T Root and HSRP Standby e (Temporarily) Si ? Even with Rapid BF 2 Access-a VLAN 2 Access Layer 2 Core Layer 3 Distribution Layer 2/3 F2 F2 Ex Ma ped fic ? PVST+: backbone Lis pire xAg Un til Leenins The nin anen opTraf 65 ? 2005 Cisco Systems, Inc. All rights reserved. Cisco Confidential RST-2032 ? Rapid PVST+: address by the protocol (one 如果分布层没有互连 回来路径黑洞 … ? Blocking link on access-b will take 50 seconds to move to forwarding return traffic black hole until then F 2 F: Forwarding B: Blocking Core Hellos second) Dr t ar g g d FB 22 STP Root and HSRP Active Access-b VLAN 2 Access-a VLAN 2 ? 802.1d: up to 50 STP seconds Secondary Root and HSRP Standby fast 30 seconds Si Si Access Layer 2 Layer 2/3 Core Layer 3 Distribution 66 ? 2005 Cisco Systems, Inc. All rights reserved. Cisco Confidential RST-2032 Layer2 分布层互连 接入层冗余链路阻塞 ? Use only if Layer 2 VLAN spanning flexibility required ? STP convergence required for uplink failure/recovery ? More complex as STP root and HSRP should match ? Distribution to distribution link required for route summarization Trunk Layer 2 VLAN 20 Data VLA