解析配置下發BGP和IS-IS缺省路由后下端業務故障
BGP會將BGP的直連路由下發到核心路由表,因此重分發BGP路由的時候,會重分發BGP的直連路由,下面就讓我們我們來看一下配置下發BGP和IS-IS缺省路由后下端業務故障的解決方法。
網絡環境
NE80-1、NE80-2、NE40-1和NE40-2四臺設備構成口字形組網結構。其中,NE80-1與NE80-2為Level-1-2路由器,NE40-1和NE40-2為Level-1路由器。
NE80-1為AS100的出口路由器,與AS200內的路由器NETWORK之間運行EBGP協議,在NE80-1和NE80-2上給NE40-1和NE40-2下發缺省路由后,出現路由環路。
故障分析
步驟 1 在NE80-1設備上執行命令display bgp routing-table,檢查NE80-1的BGP路由表,有一條到NETWORK的BGP缺省路由,如下所示,說明BGP缺省路由下發成功。
- [NE80-1] display bgp routing-table
- Total Number of Routes: 1
- BGP Local router ID is 10.10.10.1
- Status codes: * - valid, > - best, d - damped,
- h - history, i - internal, s - suppressed, S - Stale
- Origin : i - IGP, e - EGP, ? - incomplete
- Network NextHop MED LocPrf PrefVal Path/Ogn
- * 0.0.0.0 10.10.10.2 0 0 200i
步驟 2 在NE40-1和NE40-2上分別執行命令display ip routing-table,檢查NE40-1和NE40-2的IP路由表,如下所示,NE40-1的缺省路由指向了NE80-1,NE40-2的缺省路由指向了NE80-2,說明NE80-1和NE80-2下發IS-IS缺省路由成功。
- [NE40-1-isis-1] display ip routing-table
- Route Flags: R - relay, D - download to fib
- ------------------------------------------------------------------------------
- Routing Tables: Public
- Destinations : 11 Routes : 11
- Destination/Mask Proto Pre Cost Flags NextHop Interface
- 0.0.0.0/0 ISIS 15 10 D 2.2.2.1 Serial1/0/0
- 1.1.1.0/24 ISIS 15 20 D 2.2.2.1 Serial1/0/0
- 2.2.2.0/24 Direct 0 0 D 2.2.2.2 Serial1/0/0
- 2.2.2.1/32 Direct 0 0 D 2.2.2.1 Serial1/0/0
- 2.2.2.2/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- 3.3.3.0/24 ISIS 15 20 D 4.4.4.2 Serial1/0/1
- 4.4.4.0/24 Direct 0 0 D 4.4.4.1 Serial1/0/1
- 4.4.4.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- 4.4.4.2/32 Direct 0 0 D 4.4.4.2 Serial1/0/1
- 127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
- 127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- [NE40-2-isis-1] display ip routing-table
- Route Flags: R - relay, D - download to fib
- ------------------------------------------------------------------------------
- Routing Tables: Public
- Destinations : 11 Routes : 11
- Destination/Mask Proto Pre Cost Flags NextHop Interface
- 0.0.0.0/0 ISIS 15 10 D 3.3.3.1 Serial1/0/0
- 1.1.1.0/24 ISIS 15 20 D 3.3.3.1 Serial1/0/0
- 2.2.2.0/24 ISIS 15 20 D 4.4.4.1 Serial1/0/1
- 3.3.3.0/24 Direct 0 0 D 3.3.3.2 Serial1/0/0
- 3.3.3.1/32 Direct 0 0 D 3.3.3.1 Serial1/0/0
- 3.3.3.2/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- 4.4.4.0/24 Direct 0 0 D 4.4.4.2 Serial1/0/1
- 4.4.4.1/32 Direct 0 0 D 4.4.4.1 Serial1/0/1
- 4.4.4.2/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- 127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
- 127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
#p#
步驟 3 在NE80-1和NE80-2上分別執行命令display ip routing-table,檢查NE80-1和NE80-2的IP路由表,如下所示,發現NE80-1的缺省路由指向了NE80-2,NE80-2的缺省路由指向了NE80-1,形成了路由環路。
- <NE80-1> display ip routing-table
- Route Flags: R - relay, D - download to fib
- ------------------------------------------------------------------------------
- Routing Tables: Public
- Destinations : 14 Routes : 14
- Destination/Mask Proto Pre Cost Flags NextHop Interface
- 0.0.0.0/0 ISIS 15 10 D 1.1.1.2 Serial1/0/1
- 1.1.1.0/24 Direct 0 0 D 1.1.1.1 Serial1/0/1
- 1.1.1.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- 1.1.1.2/32 Direct 0 0 D 1.1.1.2 Serial1/0/1
- 2.2.2.0/24 Direct 0 0 D 2.2.2.1 Serial1/0/2
- 2.2.2.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- 2.2.2.2/32 Direct 0 0 D 2.2.2.2 Serial1/0/2
- 3.3.3.0/24 ISIS 15 20 D 1.1.1.2 Serial1/0/1
- 4.4.4.0/24 ISIS 15 20 D 2.2.2.2 Serial1/0/2
- 10.10.10.0/24 Direct 0 0 D 10.10.10.1 Serial1/0/0
- 10.10.10.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- 10.10.10.2/32 Direct 0 0 D 10.10.10.2 Serial1/0/0
- 127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
- 127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- [NE80-2] dislay ip routing-table
- Route Flags: R - relay, D - download to fib
- ------------------------------------------------------------------------------
- Routing Tables: Public
- Destinations : 11 Routes : 11
- Destination/Mask Proto Pre Cost Flags NextHop Interface
- 0.0.0.0/0 ISIS 15 10 D 1.1.1.1 Serial1/0/0
- 1.1.1.0/24 Direct 0 0 D 1.1.1.2 Serial1/0/0
- 1.1.1.1/32 Direct 0 0 D 1.1.1.1 Serial1/0/0
- 1.1.1.2/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- 2.2.2.0/24 ISIS 15 20 D 1.1.1.1 Serial1/0/0
- 3.3.3.0/24 Direct 0 0 D 3.3.3.1 Serial1/0/1
- 3.3.3.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- 3.3.3.2/32 Direct 0 0 D 3.3.3.2 Serial1/0/1
- 4.4.4.0/24 ISIS 15 20 D 3.3.3.2 Serial1/0/1
- 127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
- 127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
步驟 4 雖然上行設備通過EBGP給NE80-1下發了BGP缺省路由,但BGP協議的優先級比IS-IS協議的優先級低(BGP的優先級默認為255而IS-IS是10),所以,又將缺省路由的下一跳指向了NE80-2,這樣就形成了路由環路。
#p#
處理步驟
在NE80-2設備上執行命令undo default-route-advertise將下發的缺省路由去除后,NE80-1上執行命令display ip routing-table,可以看到NE80-1的缺省路由的下一跳已經變為10.10.10.2,該路由環路被解除,如下所示。
- [RouterA] display ip routing-table
- Route Flags: R - relay, D - download to fib
- ------------------------------------------------------------------------------
- Routing Tables: Public
- Destinations : 14 Routes : 14
- Destination/Mask Proto Pre Cost Flags NextHop Interface
- 0.0.0.0/0 BGP 255 0 D 10.10.10.2 Serial1/0/0
- 1.1.1.0/24 Direct 0 0 D 1.1.1.1 Serial1/0/1
- 1.1.1.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- 1.1.1.2/32 Direct 0 0 D 1.1.1.2 Serial1/0/1
- 2.2.2.0/24 Direct 0 0 D 2.2.2.1 Serial1/0/2
- 2.2.2.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- 2.2.2.2/32 Direct 0 0 D 2.2.2.2 Serial1/0/2
- 3.3.3.0/24 ISIS 15 20 D 1.1.1.2 Serial1/0/1
- 4.4.4.0/24 ISIS 15 20 D 2.2.2.2 Serial1/0/2
- 10.10.10.0/24 Direct 0 0 D 10.10.10.1 Serial1/0/0
- 10.10.10.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
- 10.10.10.2/32 Direct 0 0 D 10.10.10.2 Serial1/0/0
- 127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
- 127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
案例總結
對于不同的協議來說,路由的優先級是有區別的,配置缺省路由時要注意避免出現因路由協議優先級而造成的路由環路,尤其是配置IS-IS路由時。
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