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OSPF与BGP的联动特性实验案例

ops 2025/7/14 13:43:52

拓扑

1、基础配置

AR1
system
sysname AR1
int g 0/0/0
ip add 10.0.12.1 24
int g 0/0/1
ip add 10.0.13.1 24
int l 0
ip add 1.1.1.1 32AR2
system
sysname AR2
int g 0/0/0
ip add 10.0.12.2 24
int g 0/0/1
ip add 10.0.24.2 24
int l 0
ip add 2.2.2.2 32AR3
system
sysname AR3
int g 0/0/1
ip add 10.0.13.3 24
int g 0/0/0
ip add 10.0.34.3 24
int l 0
ip add 3.3.3.3 32AR4
system
sysname AR4
int g 0/0/0
ip add 10.0.34.4 24
int g 0/0/1
ip add 10.0.24.4 24
int g 0/0/2
ip add 10.0.45.4 24
int l 0
ip add 4.4.4.4 32AR5
system
sysname AR5
int g 0/0/0
ip add 10.0.45.5 24
int l 0
ip add 5.5.5.5 32

2、IGP路由配置

AR1
ospf 1 router-id 1.1.1.1
area 0
netw 10.0.12.1 0.0.0.0
netw 10.0.13.1 0.0.0.0
netw 1.1.1.1 0.0.0.0AR2
ospf 1 router-id 2.2.2.2
area 0
netw 10.0.12.2 0.0.0.0
netw 10.0.24.2 0.0.0.0
netw 2.2.2.2 0.0.0.0AR3
ospf 1 router-id 3.3.3.3
area 0
netw 10.0.13.3 0.0.0.0
netw 10.0.34.3 0.0.0.0
netw 3.3.3.3 0.0.0.0AR4
ospf 1 router-id 4.4.4.4
area 0
netw 10.0.24.4 0.0.0.0
netw 10.0.34.4 0.0.0.0
netw 4.4.4.4 0.0.0.0

3、BGP路由配置

AR1
bgp 65001
router-id 1.1.1.1
peer 2.2.2.2 as 65001
peer 2.2.2.2 con l 0
peer 3.3.3.3 as 65001
peer 3.3.3.3 con l 0
peer 4.4.4.4 as 65001
peer 4.4.4.4 con l 0AR2
bgp 65001
router-id 2.2.2.2
peer 1.1.1.1 as 65001
peer 1.1.1.1 con l 0
peer 4.4.4.4 as 65001
peer 4.4.4.4 con l 0AR3
bgp 65001
router-id 3.3.3.3
peer 1.1.1.1 as 65001
peer 1.1.1.1 con l 0
peer 4.4.4.4 as 65001
peer 4.4.4.4 con l 0AR4
bgp 65001
router-id 4.4.4.4
peer 1.1.1.1 as 65001
peer 1.1.1.1 con l 0
peer 1.1.1.1 next-hop-local 
peer 2.2.2.2 as 65001
peer 2.2.2.2 con l 0
peer 2.2.2.2 next-hop-local
peer 3.3.3.3 as 65001
peer 3.3.3.3 con l 0
peer 3.3.3.3 next-hop-local
peer 10.0.45.5 as 65002AR5
bgp 65002
router-id 5.5.5.5
peer 10.0.45.4 as 65001
netw 5.5.5.5 32

查看OSPF邻居状态

[AR1]display ospf peer brief OSPF Process 1 with Router ID 1.1.1.1Peer Statistic Information----------------------------------------------------------------------------Area Id          Interface                        Neighbor id      State    0.0.0.0          GigabitEthernet0/0/0             2.2.2.2          Full        0.0.0.0          GigabitEthernet0/0/1             3.3.3.3          Full        ----------------------------------------------------------------------------

[AR4]display ospf peer brief OSPF Process 1 with Router ID 4.4.4.4Peer Statistic Information----------------------------------------------------------------------------Area Id          Interface                        Neighbor id      State    0.0.0.0          GigabitEthernet0/0/0             3.3.3.3          Full        0.0.0.0          GigabitEthernet0/0/1             2.2.2.2          Full        ----------------------------------------------------------------------------

查看BGP邻居状态

[AR4]display bgp peerBGP local router ID : 4.4.4.4Local AS number : 65001Total number of peers : 4		  Peers in established state : 4Peer            V          AS  MsgRcvd  MsgSent  OutQ  Up/Down       State Pre
fRcv1.1.1.1         4       65001        5        5     0 00:03:16 Established    02.2.2.2         4       65001        5        5     0 00:03:16 Established    03.3.3.3         4       65001        5        5     0 00:03:14 Established    010.0.45.5       4       65002        5        6     0 00:03:10 Established    0

在AR1上查看路由信息

[AR1]display ip routing-table 5.5.5.5
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Table : Public
Summary Count : 1
Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface5.5.5.5/32  IBGP    255  0          RD   4.4.4.4         GigabitEthernet
0/0/1IBGP    255  0          RD   4.4.4.4         GigabitEthernet

因为都是默认开销,所以现在形成负载分担了,AR1-AR2-AR4-AR5为主路径,AR1-AR3-AR4-AR5为备份路径,我们修改一下IGP的COST开销。

AR1
int g 0/0/1
ospf cost 100

此时就只剩一条去往5.5.5.5的路由条目了,通过路由迭代,迭代到下一跳为AR2

[AR1]display fib 
Route Flags: G - Gateway Route, H - Host Route,    U - Up RouteS - Static Route,  D - Dynamic Route, B - Black Hole RouteL - Vlink Route
--------------------------------------------------------------------------------FIB Table:Total number of Routes : 17 Destination/Mask   Nexthop         Flag  TimeStamp     Interface      TunnelID
5.5.5.5/32         10.0.12.2       DGHU  t[7407]       GE0/0/0        0x0
4.4.4.4/32         10.0.12.2       DGHU  t[7407]       GE0/0/0        0x0
3.3.3.3/32         10.0.12.2       DGHU  t[7407]       GE0/0/0        0x0
2.2.2.2/32         10.0.12.2       DGHU  t[6823]       GE0/0/0        0x0
1.1.1.1/32         127.0.0.1       HU    t[6751]       InLoop0        0x0
10.0.13.255/32     127.0.0.1       HU    t[6751]       InLoop0        0x0
10.0.13.1/32       127.0.0.1       HU    t[6751]       InLoop0        0x0
10.0.12.255/32     127.0.0.1       HU    t[6751]       InLoop0        0x0
10.0.12.1/32       127.0.0.1       HU    t[6751]       InLoop0        0x0
255.255.255.255/32 127.0.0.1       HU    t[2]          InLoop0        0x0
127.255.255.255/32 127.0.0.1       HU    t[2]          InLoop0        0x0
127.0.0.1/32       127.0.0.1       HU    t[2]          InLoop0        0x0
127.0.0.0/8        127.0.0.1       U     t[2]          InLoop0        0x0
10.0.12.0/24       10.0.12.1       U     t[6751]       GE0/0/0        0x0
10.0.13.0/24       10.0.13.1       U     t[6751]       GE0/0/1        0x0
10.0.24.0/24       10.0.12.2       DGU   t[6827]       GE0/0/0        0x0
10.0.34.0/24       10.0.12.2       DGU   t[7407]       GE0/0/0        0x0

假设此时AR2因为某些原因重启了,AR1会切换至备份链路,当AR2的IGP收敛完成后又会切换回来,但是此时AR2的BGP并没有收敛完成路由并没有学习到位,所以AR1发送数据给AR2时就会导致丢包。

想要解决这个情况,我们可以在AR2上配置Stub Router(末节路由器),使AR2重启后IGP收敛完成后的100s内,其他设备不会以AR2为下一跳计算路由。