Lan Switching - 04. IEEE 802.1d STP
STP 실습 준비
SW1(config)#int range fa0/20 , fa0/24
SW1(config-if-range)#switchport trunk encapsulation dot1q
SW1(config-if-range)#switchport mode trunk
SW2(config)#int range fa0/22 , fa0/24
SW2(config-if-range)#switchport trunk encapsulation dot1q
SW2(config-if-range)#switchport mode trunk
SW3(config)#int range fa0/20 , fa0/22
SW3(config-if-range)#switchport trunk encapsulation dot1q
SW3(config-if-range)#switchport mode trunk
SW1,SW2,SW3#show int trunk
1. 이중화 링크 필요성
- LAN 네트워크 설계시 장애 발생가 발생할 경우, 다른 링크를 이용하여 패켓 전송이 가능하도록 하는 것을 권장한다.
- 대신, 이중화 링크를 구현하면 브리징 루프가 발생되는 문제가 있다.
- 브리징 루프 : 브로드케스트 스톰, MAC 플랩핑(동일한 MAC add가 학습되면 지워버림), 유니캐스트 중복 복제
- 브리징 루프 발생 원인 : 이중화 링크, 스위치 플러딩 동작
- 브리징 루프 방지 대책 : 스위치 특정 포트를 논리적으로 차단(Blocking)시킴
- Blocking 포트 : 프레임 송수신이 불가능한 포트를 의미한다.
① Blocking 포트는 평상시에 프레임 송수신이 차단된다.
② 그러나 사용중인 링크가 장애가 발생하면, Blocking 포트는 Forwarding 상태로 전환하여 프레임 송수신이 가능해진다.
③ 또한, 링크 장애가 복구되면, 다시 Blocking 상태로 전환된다.
- ①, ②, ③ 동작을 담당하는 프로토콜 : STP
2. STP(Spanning-Tree Protocol)
- IEEE 802.1d Spanning-Tree Protocol
- 이중화 링크에서 발생하는 브리징 루프를 방지하는 기능을 수행한다.
- BPDU 메세지를 이용하여 모니터링을 실시하여 장애 발생 및 복구를 주기적으로 감시한다.
-포트가 하나라도 UP이 되면 자동으로 활성화 된다
@SW2
SW2#sh spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0001.9608.DC2A
Cost 19
Port 24(FastEthernet0/24)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0030.A383.1759
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19 128.1 P2p
Fa0/22 Altn BLK 19 128.22 P2p ←blocking 되어있는 포트 / 추후 장애 발생시 사용
Fa0/24 Root FWD 19 128.24 P2p
3. STP 파라메터 값
- 브리지 아이디, Cost, Port-ID는 STP가 특정 포트를 Blocking 할때, 사용하는 값들이다.
1) 브리지 아이디 ← 스위치가 나오기전에 사용한 장비
- 스위치 식별자 = 64bit (우선 순위 16bit + MAC 주소 48bit)
- 우선 순위 기본값 : 32768
SW1#sh spanning-tree vlan
% Incomplete command.
SW1#sh spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee = IEEE 802.1d
Root ID Priority 32769
Address 0001.9608.DC2A = Base ethernet MAC Address : 0001.9608.DC2A
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0001.9608.DC2A ←switch 기본(자체) MAC address
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19 128.1 P2p
Fa0/20 Desg FWD 19 128.20 P2p
Fa0/24 Desg FWD 19 128.24 P2p
※우선순위값 변경 가능
@SW1
SW1(config)#spanning-tree vlan 1 priority 4096
2) Cost
- 스위치와 스위치간에 연결된 링크 메트릭
- 계산식이 없고 값이 정해져 있음
인터페이스/포트 이름 BW Cost
Ethernet 10M 100
FastEthernet 100M 19
GigaEthernet 1000M 4
10GigaEthernet 10000M 2
Ex) SW3에서 SW1까지 Cost 값은 얼마인가? 38(=19+19)
SW1[F0/24]-------------------[F0/24]SW2[F0/22]-------------------[F0/22]SW3
3) Port-ID (Port-Priority)
- 포트 번호
- 기본값 : 128.포트 번호
Ex) F0/24 -> 128.24
SW1#sh spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0001.9608.DC2A
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0001.9608.DC2A
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19★ 128.1 ★ P2p
Fa0/20 Desg FWD 19 128.20 P2p
Fa0/24 Desg FWD 19 128.24 P2p
4. STP 포트 유형
- Designated Port/DP : BPDU 송신 포트 / BPDU= 브리짓 ID,COST값, PORT ID 값 등이 저장 되어있음
- Root Port/RP : BPDU 수신 포트
Ex) DP RP
BPDU -> BPDU ->
-스위치끼리 연결된 포트는 DP가 될 수 있고 RP가 될 수도 있음.
5. STP 정보 확인
@SW1
SW1#show spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0001.9608.DC2A
This bridge is the root →→→→→→→→→→→→→→→→→→→ SW1가 Root Bridge라는 의미
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0001.9608.DC2A
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec →→→→→→→→→→→→→DP가 2초마다 나감
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/20 Desg FWD 19 128.20 P2p
Fa0/24 Desg FWD 19 128.24 P2p
Fa0/1 Desg FWD 19 128.1 P2p
@SW3
SW3#show spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0001.9608.DC2A
Cost 19
Port 20(FastEthernet0/20)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 000C.85D0.6076
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19 128.1 P2p
Fa0/20 Root FWD 19 128.20 P2p
Fa0/22 Desg FWD 19 128.22 P2p
@SW2
SW2#show spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0001.9608.DC2A
Cost 19
Port 24(FastEthernet0/24)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0030.A383.1759
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19 128.1 P2p
Fa0/22 Altn BLK 19 128.22 P2p
Fa0/24 Root FWD 19 128.24 P2p
6. STP를 이용한 포트 Blocking 과정
1) 루트 브리지 선출
- 브리지 아이디의 우선 순위가 가장 낮은 스위치
- 브리지 아이디의 MAC 주소가 가장 낮은 스위치
2) DP/RP
- DP : BPDU 송신 포트
- RP : BPDU 수신 포트
- 루트 브리지에서 BPDU 송신이 시작되기 때문에 Root Bridge 포트가 DP로 선정됨
- RP는 루트 브리지까지 Cost 값이 가장 낮은 스위치 포트로 선정됨
3) Blocking 포트
- 루트 브리지까지 Cost이 높은 스위치 포트
- Bridge-ID 값이 높은 스위치 포트
- 상대방 포트 아이디가 높은 포트에 연결된 스위치 포트
7. Blocking 포트
- Blocking 포트는 프레임 송수신이 안된다.
- Blocking 포트는 BPDU 송신이 안된다.
- 단, Blocking 포트는 BPDU 수신은 가능하다.
SW2[F0/22]-------------------------[F0/22]SW3
Blocking DP
BPDU 수신 가능
프레임 송수신 X
BPDU 송신 X
8. STP 루트 브리지 및 Blocking 수동 설정
- Root Bridge : SW2
- Backup Root Bridge : SW3
- Non Root Bridge : SW1 (F0/20 BLK)
SW2(config)#spanning-tree vlan 1 priority 4096 // spanning-tree vlan 1 root primary
SW3(config)#spanning-tree vlan 1 priority 16384 // spanning-tree vlan 1 root secondary
- 설정하고 30초 이후에 확인 실시
SW2#show spanning-tree vlan 1 <- This bridge is the root
SW1#show spanning-tree vlan 1 <- F0/20 BLK
[실습]
TRUNK 설정
@SW1
en
conf t
int f0/22
switchport trunk encapsulation dot1q
switchport mode trunk
!
int f0/24
switchport trunk encapsulation dot1q
switchport mode trunk
@SW2
en
conf t
int f0/20
switchport trunk encapsulation dot1q
switchport mode trunk
!
int f0/22
switchport trunk encapsulation dot1q
switchport mode trunk
!
int f0/24
switchport trunk encapsulation dot1q
switchport mode trunk
!
@SW3
en
conf t
int f0/22
switchport trunk encapsulation dot1q
switchport mode trunk
!
int f0/24
switchport trunk encapsulation dot1q
switchport mode trunk
!
@SW4
en
conf t
int f0/20
switchport trunk encapsulation dot1q
switchport mode trunk
!
int f0/22
switchport trunk encapsulation dot1q
switchport mode trunk
!
int f0/24
switchport trunk encapsulation dot1q
switchport mode trunk
!
SW4 의 f0/20 f0/24 BLK
- Root Bridge : SW1 ←4096
- Backup Root Bridge : SW2 ←16384
- Non Root Bridge : SW4 (F0/20&F0/24 BLK)
@SW1
spanning-tree vlan 1 spanning-tree vlan 1 priority 4096
end
sh spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 0006.2A0A.9919
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 4097 (priority 4096 sys-id-ext 1)
Address 0006.2A0A.9919
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/22 Desg FWD 19 128.22 P2p
Fa0/24 Desg FWD 19 128.24 P2p
@SW2
sh spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 0006.2A0A.9919
Cost 19
Port 24(FastEthernet0/24)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 16385 (priority 16384 sys-id-ext 1)
Address 0002.4AA4.9A0E
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/20 Desg FWD 19 128.20 P2p
Fa0/22 Desg FWD 19 128.22 P2p
Fa0/24 Root FWD 19 128.24 P2p
@SW3
spanning-tree vlan 1 priority 32768
sh spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 0006.2A0A.9919
Cost 38
Port 22(FastEthernet0/22)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0004.9ADC.5ECD
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/22 Root FWD 19 128.22 P2p
Fa0/24 Altn BLK 19 128.24 P2p
@SW4
#sh spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 0006.2A0A.9919
Cost 19
Port 22(FastEthernet0/22)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 000C.CF65.AAE0
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/20 Altn BLK 19 128.20 P2p
Fa0/22 Root FWD 19 128.22 P2p
Fa0/24 Desg FWD 19 128.24 P2p
#sh spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 0006.2A0A.9919
Cost 19
Port 22(FastEthernet0/22)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 000C.CF65.AAE0
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/20 Altn BLK 19 128.20 P2p
Fa0/22 Root FWD 19 128.22 P2p
Fa0/24 Desg FWD 19 128.24 P2p
9. STP 타이머
- Hello 타이머 : BPDU 전송 주기, 기본값 2초
- Forward Delay 타이머 : 스위치 포트가 Forwarding 상태로 전환되는데 필요한 시간, 기본값 15초
- Max Age 타이머 : Blocking 포트로 새로운 BPDU를 수신하면, 기존의 BPDU랑 비교하는 시간, 기본값 20초
10. STP 포트 상태
- Disable : 포트 비활성화 상태(shutdown, 케이블 연결 X)
- Blocking : 브리징 루프를 방지하기 위해서 포트를 논리적으로 차단한 상태
프레임 송수신 X, BPDU 송신 X
단, BPDU 수신 O
- Listening : 포트가 동작하기 위한 준비 단계
루트 브리지까지 Cost 값 계산
DP 선정/RP 선정 결정
Forward Delay 타이머 적용 (15초)
- Learning : MAC 주소 단계
Forward Delay 타이머 적용 (15초)
- Forwarding : 프레임 송수신 가능 상태
- IEEE 802.1d STP는 컨버전스가 30초, 50초라는 지연이 있기 때문에 현재 내부망에서는 권장하지 않는다.
SecureCRT와 장비를 이용한 실습
[ LIS →LRN →FWD] 확인
SW1# debug spanning-tree events
@SW2
int fa0/22
shutdown
SW1 STP 디버깅 확인
*Mar 1 02:33:02.251: STP: VLAN0001 new root port Fa0/20, cost 38
*Mar 1 02:33:02.251: STP: VLAN0001 Fa0/20 -> listening
*Mar 1 02:33:03.239: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/24, changed state to down
*Mar 1 02:33:03.239: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to down
*Mar 1 02:33:04.251: %LINK-3-UPDOWN: Interface FastEthernet0/24, changed state to down
*Mar 1 02:33:04.251: STP: VLAN0001 sent Topology Change Notice on Fa0/20
*Mar 1 02:33:17.251: STP: VLAN0001 Fa0/20 -> learning
*Mar 1 02:33:32.251: STP: VLAN0001 Fa0/20 -> forwarding
*Mar 1 02:33:33.251: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to up
SW1#sh spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 0014.1caf.a100
Cost 38
Port 20 (FastEthernet0/20)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 000e.3889.d700
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/20 Root FWD 19 128.20 P2p
@SW2
int fa0/22
no shutdown
@SW1
SW1#
*Mar 1 02:36:15.559: %LINK-3-UPDOWN: Interface FastEthernet0/24, changed state to up
*Mar 1 02:36:16.575: set portid: VLAN0001 Fa0/24: new port id 8018
*Mar 1 02:36:16.575: STP: VLAN0001 Fa0/24 -> listening
*Mar 1 02:36:17.575: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/24, changed state to up
*Mar 1 02:36:17.655: STP: VLAN0001 new root port Fa0/24, cost 19
*Mar 1 02:36:17.655: STP: VLAN0001 sent Topology Change Notice on Fa0/24
*Mar 1 02:36:17.659: STP: VLAN0001 Fa0/20 -> blocking
*Mar 1 02:36:18.659: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to down
*Mar 1 02:36:31.575: STP: VLAN0001 Fa0/24 -> learning
*Mar 1 02:36:46.575: STP: VLAN0001 Fa0/24 -> forwarding
*Mar 1 02:36:47.575: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to up
[BLK 20초 → LIS →LRN →FWD] 확인
SW1# debug spanning-tree events
@SW2
int fa0/22
shutdown
SW1 STP 디버깅 확인
BLK 20초 → LIS →LRN →FWD
Spanning Tree event debugging is on
SW1#
*Mar 1 03:05:26.627: STP: VLAN0001 heard root 16385-000d.bd19.4f80 on Fa0/20
*Mar 1 03:05:28.603: STP: VLAN0001 heard root 16385-000d.bd19.4f80 on Fa0/20
*Mar 1 03:05:30.603: STP: VLAN0001 heard root 16385-000d.bd19.4f80 on Fa0/20
*Mar 1 03:05:32.603: STP: VLAN0001 heard root 16385-000d.bd19.4f80 on Fa0/20
*Mar 1 03:05:34.603: STP: VLAN0001 heard root 16385-000d.bd19.4f80 on Fa0/20
*Mar 1 03:05:36.603: STP: VLAN0001 heard root 16385-000d.bd19.4f80 on Fa0/20
*Mar 1 03:05:38.603: STP: VLAN0001 heard root 16385-000d.bd19.4f80 on Fa0/20
*Mar 1 03:05:40.603: STP: VLAN0001 heard root 16385-000d.bd19.4f80 on Fa0/20
*Mar 1 03:05:42.603: STP: VLAN0001 heard root 16385-000d.bd19.4f80 on Fa0/20
*Mar 1 03:05:44.603: STP: VLAN0001 heard root 16385-000d.bd19.4f80 on Fa0/20
*Mar 1 03:05:44.631: STP: VLAN0001 Fa0/20 -> listening
*Mar 1 03:05:45.631: STP: VLAN0001 Topology Change rcvd on Fa0/20
*Mar 1 03:05:45.631: STP: VLAN0001 sent Topology Change Notice on Fa0/24
*Mar 1 03:05:59.631: STP: VLAN0001 Fa0/20 -> learning
*Mar 1 03:06:14.631: STP: VLAN0001 sent Topology Change Notice on Fa0/24
*Mar 1 03:06:14.631: STP: VLAN0001 Fa0/20 -> forwarding
SW1#sh spanning-tree vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 0014.1caf.a100
Cost 19
Port 24 (FastEthernet0/24)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 000e.3889.d700
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 15
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/20 Desg FWD 19 128.20 P2p
Fa0/24 Root FWD 19 128.24 P2p
@SW2
int f0/22
no shutdown
[SW1 → PC 연결]
SWx[F0/1]----------------------PC
SW1#debug spanning-tree events
@SW1
conf t
int fa0/1
shutdown
SW1(config-if)#no shutdown
SW1(config-if)#
*Mar 1 03:16:41.479: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up
*Mar 1 03:16:44.163: set portid: VLAN0001 Fa0/1: new port id 8001
*Mar 1 03:16:44.163: STP: VLAN0001 Fa0/1 -> listening
*Mar 1 03:16:45.163: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up
*Mar 1 03:16:59.163: STP: VLAN0001 Fa0/1 -> learning
*Mar 1 03:17:14.163: STP: VLAN0001 sent Topology Change Notice on Fa0/24
*Mar 1 03:17:14.163: STP: VLAN0001 Fa0/1 -> forwarding
<PortFast>
SW1#debug spanning-tree events
@SW1
int f0/1
shutdown
SW1(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 FastEthernet0/1 but will ^only have effect when the interface is in a non-trunking mode.^ ←하지말라고 하는데도 불구하고 자꾸해서 트렁크 설정시 portfast 설정해도 적용 안됨
SW1(config-if)#no shutdown
SW1(config-if)#
*Mar 1 03:24:08.375: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up
*Mar 1 03:24:10.899: set portid: VLAN0001 Fa0/1: new port id 8001
*Mar 1 03:24:10.899: STP: VLAN0001 Fa0/1 ->jump to forwarding from blocking ★
*Mar 1 03:24:11.899: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up
Switch-Router 연결 후 Inter-VLAN 설정을 위해 SW-R이 trunk mode 로 되어있을시 portfast 하려면
int fa0/10
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree portfast trunk
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