如圖所示,在網絡中有3台路由器通過IS-IS協定實作路由互通,且Router-A如Router-B自檢通過一台二層交換機實作互聯。現要求當Router-A與Router-B之間經交換機的鍊路出現故障時,這兩台路由器能快速地對故障效果做出反應,并把流量切換至經Router-C鍊路轉發。
本示例采用IS-IS與動态BFD關聯的特性,要實作主備鍊路切換,這就涉及主備路由的問題。如果沒有為IS-IS接口配置任何開銷值,IS-IS接口的預設開銷值均為10(開銷類型是narrow),是以預設情況下,Router-A通路172,16.1.0/24網段時走經二層交換機鍊路出現故障時可将流量計是切換至經Router-C的備份鍊路轉發。當然,同樣在此之前配置各路由器的接口IP位址以及IS-IS基本功能,實作路由之間路由可達。
1) 配置各路由器的接口IP位址
【Router-A上的配置】
interface GigabitEthernet1/0/0
ip address 10.1.1.1 255.255.255.0
#
interface GigabitEthernet2/0/0
ip address 10.3.3.1 255.255.255.0
#
【Router-B上的配置】
interface GigabitEthernet1/0/0
ip address 10.2.2.2 255.255.255.0
#
interface GigabitEthernet2/0/0
ip address 10.3.3.2 255.255.255.0
#
interface GigabitEthernet3/0/0
ip address 172.16.1.1 255.255.255.0
#
【Router-C上的配置】
#
interface GigabitEthernet1/0/0
ip address 10.1.1.2 255.255.255.0
#
interface GigabitEthernet2/0/0
ip address 10.2.2.1 255.255.255.0
#
2) 配置各路由器上的IS-IS基本功能
假設3台路由器的系統ID分别配置為0000.0000.0001、0000.0000.0002、0000.0000.0003,同處于一個骨幹網區域10中(均為L2路由器),均使能預設的1後IS-IS路由程序。
【Router-A上的配置】
isis 1
is-level level-2
network-entity 10.0000.0000.0001.00
#
interface GigabitEthernet1/0/0
ip address 10.1.1.1 255.255.255.0
isis enable 1
#
interface GigabitEthernet2/0/0
ip address 10.3.3.1 255.255.255.0
isis enable 1
#
【Router-B上的配置】
isis 1
is-level level-2
network-entity 10.0000.0000.0002.00
#
interface GigabitEthernet1/0/0
ip address 10.2.2.2 255.255.255.0
isis enable 1
#
interface GigabitEthernet2/0/0
ip address 10.3.3.2 255.255.255.0
isis enable 1
#
interface GigabitEthernet3/0/0
ip address 172.16.1.1 255.255.255.0
isis enable 1
#
【Router-C上的配置】
isis 1
is-level level-2
network-entity 10.0000.0000.0003.00
#
interface GigabitEthernet1/0/0
ip address 10.1.1.2 255.255.255.0
isis enable 1
#
interface GigabitEthernet2/0/0
ip address 10.2.2.1 255.255.255.0
isis enable 1
#
【以上配置好後,使用display isis peer指令檢視鄰居】
[Router-A]dis isis peer
Peer information for ISIS(1)
System Id Interface Circuit Id State HoldTime Type PRI
---------------------------------------------------------------------------
0000.0000.0003 GE1/0/0 0000.0000.0003.01 Up 8s L2 64
0000.0000.0002 GE2/0/0 0000.0000.0001.02 Up 28s L2 64
Total Peer(s): 2
[Router-A]
[Router-B]dis isis peer
Peer information for ISIS(1)
System Id Interface Circuit Id State HoldTime Type PRI
--------------------------------------------------------------------------
0000.0000.0003 GE1/0/0 0000.0000.0003.02 Up 8s L2 64
0000.0000.0001 GE2/0/0 0000.0000.0001.02 Up 8s L2 64
Total Peer(s): 2
[Router-B]
【檢視Router-A的ISIS路由表】
<Router-A>dis isis route
Route information for ISIS(1)
-----------------------------
ISIS(1) Level-2 Forwarding Table
--------------------------------
IPV4 Destination IntCost ExtCost ExitInterface NextHop Flags
--------------------------------------------------------------------------
10.3.3.0/24 10 NULL GE2/0/0 Direct D/-/L/-
172.16.1.0/24 20 NULL GE2/0/0 10.3.3.2 A/-/-/-
10.2.2.0/24 20 NULL GE1/0/0 10.1.1.2 A/-/-/-
GE2/0/0 10.3.3.2
10.1.1.0/24 10 NULL GE1/0/0 Direct D/-/L/-
Flags: D-Direct, A-Added to URT, L-Advertised in LSPs, S-IGP Shortcut,
U-Up/Down Bit Set
3) 在Router-A和Router-B上分别使能IS-IS程序下的BFD特性,假定制定最小發送和接收間隔為100ms,本地檢測時間倍數為4(這些參數可不配置,直接采用預設值)
【Router-A上配置】
#
bfd
#
isis 1
is-level level-2
bfd all-interfaces enable
network-entity 10.0000.0000.0001.00
#
interface GigabitEthernet1/0/0
ip address 10.1.1.1 255.255.255.0
isis enable 1
#
interface GigabitEthernet2/0/0
ip address 10.3.3.1 255.255.255.0
isis enable 1
isis bfd enable
isis bfd min-tx-interval 100 min-rx-interval 100 detect-multiplier 4
#
【Router-B上配置】
bfd
#
isis 1
is-level level-2
bfd all-interfaces enable
network-entity 10.0000.0000.0002.00
face GigabitEthernet0/0/2
#
interface GigabitEthernet1/0/0
ip address 10.2.2.2 255.255.255.0
isis enable 1
#
interface GigabitEthernet2/0/0
ip address 10.3.3.2 255.255.255.0
isis enable 1
isis bfd enable
isis bfd min-tx-interval 100 min-rx-interval 100 detect-multiplier 4
#
【配置好後,在Router-A或Router-B上執行display isis bfd session all】指令便可以檢視BFD參數已生效,并且BFD會話狀态為Up。
[Router-B]dis isis bfd session all
BFD session information for ISIS(1)
-----------------------------------
Peer System ID : 0000.0000.0003 Interface : GE1/0/0
TX : 12500 BFD State : down Peer IP Address : 10.2.2.1
RX : 12500 LocDis : 8192 Local IP Address: 10.2.2.2
Multiplier : 0 RemDis : 0 Type : L2
Diag : No diagnostic information
Peer System ID : 0000.0000.0001 Interface : GE2/0/0
TX : 100 BFD State : up Peer IP Address : 10.3.3.1
RX : 100 LocDis : 8193 Local IP Address: 10.3.3.2
Multiplier : 4 RemDis : 8193 Type : L2
Diag : No diagnostic information
Total BFD sessi
【現對Router-B的G2/0/0端口執行shutdown指令,模拟主鍊路故障。】此時檢視Router-A的IP路由表,可以看出,到達172.16.1.0/24的路由下一跳位址為10.1.1.2(Router-C的G1/0/0接口的IP位址),流量在主鍊路Router-A-Router-c -Router-B上傳輸。
<Router-A>dis isis route
Route information for ISIS(1)
-----------------------------
ISIS(1) Level-2 Forwarding Table
--------------------------------
IPV4 Destination IntCost ExtCost ExitInterface NextHop Flags
--------------------------------------------------------------------------
10.3.3.0/24 10 NULL GE2/0/0 Direct D/-/L/-
172.16.1.0/24 30 NULL GE1/0/0 10.1.1.2 A/-/-/-
10.2.2.0/24 20 NULL GE1/0/0 10.1.1.2 A/-/-/-
10.1.1.0/24 10 NULL GE1/0/0 Direct D/-/L/-
Flags: D-Direct, A-Added to URT, L-Advertised in LSPs, S-IGP Shortcut,
U-Up/Down Bit Set
當主鍊路恢複正常後,到達172.16.1.0/24的路由又将恢複為主鍊路,因為主鍊路的路由開銷(10)要低于備份鍊路的路由開銷(20),優先級更高。