实验拓朴:
R1----------------- R2 --------------------R3
IBGP
全网OSPF
实验基本配置：
R1：
interface Loopback0
ip address 1.1.1 .1 255.255.255.255
!
interface Serial1/1
ip address 10.1.12 .1 255.255.255.0
!
router ospf 1
router-id 1.1.1 .1
log-adjacency-changes
network 10.1.12 .0 0.0.0.255 area 0
!
router bgp 1
bgp router-id 1.1.1 .1
bgp log-neighbor-changes
neighbor 10.1.12 .2 remote-as 1
no auto-summary
!
R2：
interface Loopback0
ip address 2.2.2 .2 255.255.255.255
!
interface Serial1/0
ip address 10.1.12 .2 255.255.255.0
!
interface Serial1/1
ip address 10.1.23 .2 255.255.255.0
!
router ospf 1
router-id 2.2.2 .2
log-adjacency-changes
network 10.1.12 .0 0.0.0.255 area 0
network 10.1.23 .0 0.0.0.255 area 0
!
router bgp 1
bgp router-id 2.2.2 .2
bgp log-neighbor-changes
network 3.3.3 .3 mask 255.255.255.255
neighbor 10.1.12 .1 remote-as 1
no auto-summary
!
R3：
interface Loopback0
ip address 3.3.3 .3 255.255.255.255
!
interface Serial1/0
ip address 10.1.23 .3 255.255.255.0
!
router ospf 1
router-id 3.3.3 .3
log-adjacency-changes
network 3.3.3 .3 0.0.0.0 area 0
network 10.1.23 .0 0.0.0.255 area 0
!
实验现象：
R1#sh ip bgp
BGP table version is 1, local router ID is 1.1.1 .1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
* i3.3.3 .3/32 10.1.23 .3 65 100 0 i
R1#sh ip bgp 3.3.3 .3
BGP routing table entry for 3.3.3 .3/32, version 0
Paths: (1 available, no best path)
Not advertised to any peer
Local
Origin IGP, metric 65, localpref 100, valid, internal, not synchronized
R1#sh ip route 3.3.3 .3
Routing entry for 3.3.3 .3/32
Known via "ospf 1", distance 110, metric 129, type intra area
Last update from 10.1.12 .2 on Serial1/1, 00:01:01 ago
Routing Descriptor Blocks:
* 10.1.12 .2, from 3.3.3.3, 00:01:01 ago, via Serial1/1
Route metric is 129, traffic share count is 1
R3的lo0 3.3.3 .3 在R2上通过BGP中network 通告给R1，但R1 收到的 OSPF路由的router-id (show ip route 3.3.3.3) 为3.3.3.3， R1 BGP路由的router-id (show ip bgp 3.3.3.3) 为2.2.2.2 ，两者不一致，未同步，show ip bgp 中有3.3.3.3，但非最优路径 无> .
更改R2 BGP配置中的router-id 为 3.3.3 .3 ，结果：
R1#sh ip bgp
BGP table version is 2, local router ID is 1.1.1 .1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>i3.3.3 .3/32 10.1.23 .3 65 100 0 i
R1#sh ip bgp 3.3.3 .3
BGP routing table entry for 3.3.3 .3/32, version 2
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Flag: 0x208
Not advertised to any peer
Local
Origin IGP, metric 65, localpref 100, valid, internal, synchronized, best
扩展
R2#sh ip route 3.3.3 .3
Routing entry for 3.3.3 .3/32
Known via "ospf 1", distance 110, metric 65, type intra area
Advertised by bgp 1
Last update from 10.1.23 .3 on Serial1/1, 00:12:34 ago
Routing Descriptor Blocks:
* 10.1.23 .3, from 3.3.3.3, 00:12:34 ago, via Serial1/1
Route metric is 65, traffic share count is 1
R2#sh ip bgp 3.3.3 .3
BGP routing table entry for 3.3.3 .3/32, version 2
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Advertised to non peer-group peers:
Local
Origin IGP, metric 65, localpref 100, weight 32768, valid, sourced, local, best
R2 在开启同步的情况下 show ip bgp 3.3.3 .3 始终有> ，本地通告 net 3.3.3.3 ，同样OSPF和BGP的router-id 不一致 , 但路由可以最优.
理解同步检查用在什么时候 ：IBGP传过来的路由，进行检查.
