解析配置下發(fā)BGP和IS-IS缺省路由后下端業(yè)務(wù)故障
BGP會(huì)將BGP的直連路由下發(fā)到核心路由表,因此重分發(fā)BGP路由的時(shí)候,會(huì)重分發(fā)BGP的直連路由,下面就讓我們我們來看一下配置下發(fā)BGP和IS-IS缺省路由后下端業(yè)務(wù)故障的解決方法。
網(wǎng)絡(luò)環(huán)境
NE80-1、NE80-2、NE40-1和NE40-2四臺(tái)設(shè)備構(gòu)成口字形組網(wǎng)結(jié)構(gòu)。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(nèi)的路由器NETWORK之間運(yùn)行EBGP協(xié)議,在NE80-1和NE80-2上給NE40-1和NE40-2下發(fā)缺省路由后,出現(xiàn)路由環(huán)路。
故障分析
步驟 1 在NE80-1設(shè)備上執(zhí)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(fā)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(zhí)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(fā)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(zhí)行命令display ip routing-table,檢查NE80-1和NE80-2的IP路由表,如下所示,發(fā)現(xiàn)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(huán)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(shè)備通過EBGP給NE80-1下發(fā)了BGP缺省路由,但BGP協(xié)議的優(yōu)先級比IS-IS協(xié)議的優(yōu)先級低(BGP的優(yōu)先級默認(rèn)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(huán)路。
#p#
處理步驟
在NE80-2設(shè)備上執(zhí)行命令undo default-route-advertise將下發(fā)的缺省路由去除后,NE80-1上執(zhí)行命令display ip routing-table,可以看到NE80-1的缺省路由的下一跳已經(jīng)變?yōu)?0.10.10.2,該路由環(huán)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(jié)
對于不同的協(xié)議來說,路由的優(yōu)先級是有區(qū)別的,配置缺省路由時(shí)要注意避免出現(xiàn)因路由協(xié)議優(yōu)先級而造成的路由環(huán)路,尤其是配置IS-IS路由時(shí)。
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