Understanding RSTP Through Configuration

Cisco製品はデフォルトコンフィグでも(R)STPが動作する
それでも、STPのコンフィグを行えると利点がある
- 所望のswitchをSTP root switchに選出させることができるなどの利点がある

The Need for Multiple Spanning Trees

VLANの出現前までは CST: common spanning tree トポロジーを考えればよかった
VLANの登場により、負荷分散の検知から、同一の物理接続上で複数の論理的なspanning treeを考えるべきになった

STP Modes and Standards

Switch>enable
Switch#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#spanning-tree mode ?
  pvst        Per-Vlan spanning tree mode
  rapid-pvst  Per-Vlan rapid spanning tree mode
Switch(config)#spanning-tree mode

種類

Name	Base	# Trees	Original IEEE Standard	Config Parameter
STP	STP	1 (CST)	802.1D
PVST+	STP	1/VLAN	802.1D	pvst
RSTP	RSTP	1 (CST)	802.1w
Rapid PVST	RSTP	1/VLAN	802.1w	rapid-pvst
MSTP	RSTP	1 or more	802.1s	mst

Packet Tracerではmstは無かった
MSTI: Multi Spanning Tree Instances
- 複数のSTを選べるが、VLANごとに1つを要求するものではない

SW2#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol rstp
  Root ID    Priority    24577
             Address     0090.0CA7.83C1
             This bridge is the root
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    24577  (priority 24576 sys-id-ext 1)
             Address     0090.0CA7.83C1
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  20

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/11           Desg BLK 19        128.11   P2p
Gi0/1            Desg BLK 4         128.25   P2p
Gi0/2            Desg BLK 4         128.26   P2p

SW2#

これ:

  Spanning tree enabled protocol rstp

The Bridge ID and System ID Extension

per-VLANであれMSTであれ、複数のSpanning Treeを扱うとなると、VLANとVLAN trunkingを考える必要が出てくる
- ゆえに、現在ではRSTPとMSTPは802.1Q標準の一部
- VLAN taggingの標準
BIDを拡張する
- Priority 2バイト(16ビット)の内訳
- 上位4ビット: priority
- 下位12ビット: System ID Extension
  - 典型的にはVLANのID(12bit)を格納する

Switch#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     0001.428C.987C
             Cost        4
             Port        25(GigabitEthernet0/1)
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0030.A396.EE00
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  20

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/11           Desg FWD 19        128.11   P2p
Gi0/1            Root FWD 4         128.25   P2p
Gi0/2            Desg FWD 4         128.26   P2p

Switch#

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)

こうした経緯により、priorityには4096(2^12)の倍数しか設定できない

Switch(config)#spanning-tree vlan 1 priority ?
  <0-61440>  bridge priority in increments of 4096

数値を直接指定するのではなく、便利なエイリアスがある
root primary
- 24576 (32768 - 8192)
- デフォルト値32768よりも小さい = 優先される

Switch#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
...

root secondary
- 28672 (32768 - 4096)
- デフォルト値32768よりも小さい = 優先される
- primaryよりは大きい = 優先されない

Switch(config)#spanning-tree vlan 1 root secondary
Switch(config)#end
Switch#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    28673
...

root primaryは、現rootが24576以下をすでに使用していれば、4096を用いることになっているらしい
- 【補】Packet Tracerでは、rootを24576にして試したら、20480になった

How Switches Use the Priority and System ID Extension

SW2#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
SW2(config)#spanning-tree vlan 1 priority 24576
SW2(config)#end
SW2#

SW2#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
...

抜粋

...
SW2(config)#spanning-tree vlan 1 priority 24576
...
  Root ID    Priority    24577
...

24577 = 0b(0110 | 0000 0000 0001)

VLAN IDが12bitなので単純足し算

RSTP Methods to Support Multiple Spanning Trees

IEEE標準のRSTPとCisco独自のRPVST+の違い

	RSTP	RPVST+
# tree	1 (CST)	1 / VLAN
# message / network	1	1 / VLAN
Destination MAC Address (multicast)	`0180.C200.0000`	`0100.0CCC.CCCD`
VLAN tagging (802.1Q header)	なし	あり
extra TLV: type-length value	なし	あり (VLAN IDの識別用)
12-bit System ID Extension部分の解釈	VLANなし	VLAN ID

Other RSTP Configuration Options

Switch Priority
- spanning-tree vlan x priority y
Primary and Secondary Root Switches
- spanning-tree vlan x root (primary|secondary)
Port Costs
- spanning-tree [vlan x] cost y
- Packet Tracerには無さげ

Configuring Layer 2 EtherChannel

複数のinterfaceを論理的にまとめるやつ
- すべてをパラレルに用いる
- 負荷分散
- 障害時のSTP convergenceの回避

Configuring a Manual Layer 2 EtherChannel

これになりたい:

設定を行わない場合、たんにSTPによって片方がblocking (discarding) stateによる

設定

SW1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
SW1(config)#interface fa0/14
SW1(config-if)#channel-group 1 mode on
SW1(config-if)#
Creating a port-channel interface Port-channel 1

%LINK-5-CHANGED: Interface Port-channel1, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel1, changed state to up

SW1(config-if)#interface fa 0/15
SW1(config-if)#channel-group 1 mode on
SW1(config-if)#end
SW1#
%SYS-5-CONFIG_I: Configured from console by console

確認

SW1#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     00E0.F786.AD08
             Cost        9
             Port        27(Port-channel1)
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     00E0.F795.E265
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  20

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Po1              Root LRN 9         128.27   Shr

cf. 未設定

SW2#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     00E0.F786.AD08
             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     00E0.F786.AD08
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  20

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/17           Desg FWD 19        128.17   P2p
Fa0/16           Desg FWD 19        128.16   P2p

...
             Port        27(Port-channel1)
...
Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Po1              Root LRN 9         128.27   Shr

port-channel interface Po1ができている

SW1#show etherchannel summary
Flags:  D - down        P - in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      f - failed to allocate aggregator
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port


Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+----------------------------------------------

1      Po1(SU)           -      Fa0/14(P) Fa0/15(P)

Configuring Dynamic EtherChannels

SW1(config-if)#channel-group 1 mode ?
  active     Enable LACP unconditionally
  auto       Enable PAgP only if a PAgP device is detected
  desirable  Enable PAgP unconditionally
  on         Enable Etherchannel only
  passive    Enable LACP only if a LACP device is detected
SW1(config-if)#channel-group 1 mode

active, auto, desirable, passive は動的にEtherChannelを設定する
動的にnegotiateするプロトコルは2種類ある:
- PAgP: Port Aggregation Protocol
- Cisco独自
- 8本まで
- LACP: Link Aggregation Control Protocol
- based on IEEE 802.3ad
- アクティブ8本 + スタンバイ8本まで

	on	desirable	auto	active	passive
on	static EtherChannel	Do Not Use	Do Not Use	Do Not Use	Do Not Use
desirable	Do Not Use	PAgP	PAgP
auto	Do Not Use	PAgP
active	Do Not Use			LACP	LACP
passive	Do Not Use			LACP

desirable - autoで設定してみる

SW1: desirable

SW1(config)#interface f0/14
SW1(config-if)#channel-group 1 mode desirable
SW1(config-if)#exit
SW1(config-if)#interface f0/15
SW1(config-if)#channel-group 1 mode desirable
SW1(config-if)#
%LINK-3-UPDOWN: Interface Port-channel1, changed state to down

%LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel1, changed state to down

SW1(config-if)#

SW2: auto

SW2(config)#interface f0/16
SW2(config-if)#channel-group 1 mode auto
SW2(config-if)#
Creating a port-channel interface Port-channel 1

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/16, changed state to down

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/16, changed state to up

SW2(config-if)#exit
SW2(config)#interface f0/17
SW2(config-if)#channel-group 1 mode auto
SW2(config-if)#
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/17, changed state to down

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/17, changed state to up

%LINK-5-CHANGED: Interface Port-channel1, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel1, changed state to up

SW2(config-if)#
SW2(config-if)#end
SW2#
%SYS-5-CONFIG_I: Configured from console by console

確認

SW1

SW1#show etherchannel port-channel 
                Channel-group listing:
                ----------------------

Group: 1
----------
                Port-channels in the group:
                ---------------------------

Port-channel: Po1
------------

Age of the Port-channel   = 00d:00h:30m:25s
Logical slot/port   = 2/1       Number of ports = 2
GC                  = 0x00000000      HotStandBy port = null
Port state          = Port-channel 
Protocol            =   PAGP
Port Security       = Disabled

Ports in the Port-channel:

Index   Load   Port     EC state        No of bits
------+------+------+------------------+-----------
  0     00     Fa0/14   Desirable-Sl       0
  0     00     Fa0/15   Desirable-Sl       0
Time since last port bundled:    00d:00h:02m:21s    Fa0/15

SW2

SW2#show etherchannel port-channel 
                Channel-group listing:
                ----------------------

Group: 1
----------
                Port-channels in the group:
                ---------------------------

Port-channel: Po1
------------

Age of the Port-channel   = 00d:00h:03m:19s
Logical slot/port   = 2/1       Number of ports = 2
GC                  = 0x00000000      HotStandBy port = null
Port state          = Port-channel 
Protocol            =   PAGP
Port Security       = Disabled

Ports in the Port-channel:

Index   Load   Port     EC state        No of bits
------+------+------+------------------+-----------
  0     00     Fa0/16   Automatic          0
  0     00     Fa0/17   Automatic          0
Time since last port bundled:    00d:00h:02m:59s    Fa0/17

Physical Interface Configuration and EtherChannels

新しい物理interfaceをPort Channelに追加するとき、Port Channel内の既存のinterfaceと設定が一致していないといけない
- speed
- duplex
- などなど
【補】
- Packet Tracerでは全然違ってもPort Channelを組めてしまった

EtherChannel Load Distribution

MACアドレスの学習プロセスは、物理的なinterfaceではなく、PortChannel interfaceにより行われるようになる
- 「このMACアドレスのデバイスは、このPortChannelの向こうにいる」
ではPortChannel interfaceからframeを送出するさい、どの物理interfaceを使うか？
負荷分散の話になってくる

Configuration Options for EtherChannel Load Distribution

global configで、(src|dst|src-dst)-(mac|ip|port) による負荷分散が利用可能
- source/destination/両方の
- 【疑問点】テキストには「Both」、Packet Tracerのヘルプには「XOR」と書いてある…
- MACアドレス/IPアドレス/TCP・UDPポート番号
【補】Packet TracerではL4の情報による負荷分散はサポートされていなかった

Switch(config)#port-channel load-balance ?
  dst-ip       Dst IP Addr
  dst-mac      Dst Mac Addr
  src-dst-ip   Src XOR Dst IP Addr
  src-dst-mac  Src XOR Dst Mac Addr
  src-ip       Src IP Addr
  src-mac      Src Mac Addr

The Effects of the EtherChannel Load Distribution Algorithm

SW1(config)#port-channel load-balance src-mac
SW1(config)#end
SW1#
%SYS-5-CONFIG_I: Configured from console by console
SW1#show etherchannel load-balance 
EtherChannel Load-Balancing Operational State (src-mac):
Non-IP: Source MAC address
  IPv4: Source MAC address
  IPv6: Source MAC address

下記コマンドでロードバランシングのテストができるらしいが、Packet Tracerではできなかった

SW1#test etherchannel load-balance interface po1 mac 0200.0000.0001 0200.1111.1111
         ^
% Invalid input detected at '^' marker.
	
SW1#test etherchannel

D.Horiyama's output

CCNA試験対策 ch10 RSTP and EtherChannel Configuration

Understanding RSTP Through Configuration

The Need for Multiple Spanning Trees

STP Modes and Standards

The Bridge ID and System ID Extension

How Switches Use the Priority and System ID Extension

RSTP Methods to Support Multiple Spanning Trees

Other RSTP Configuration Options

Configuring Layer 2 EtherChannel

Configuring a Manual Layer 2 EtherChannel

Configuring Dynamic EtherChannels

Physical Interface Configuration and EtherChannels

EtherChannel Load Distribution

Configuration Options for EtherChannel Load Distribution

The Effects of the EtherChannel Load Distribution Algorithm