bgp -1 ebgp邻居，下一条属性， 路由黑洞， BGP同步
需求1： 如图建立ebgp，和ibgp邻居。
ebgp 邻居建立： 1 使用物理接口
2 使用换回口， 同时增加到达对方lo 口的静态路由 ，配置ebgp多跳
ibgp 邻居建立： 使用换回口建立， igp 全网互通，
需求2： r4 上通过bgp 通告 10.1.44.4/32 ， 使r2 可以达到
r4 建立lo 1 10.1.44.4 /32 ， bgp中network
1 r4，r1 ，r1 bgp 路由如下：
[R4-bgp]disp bgp rou
BGP Local router ID is 10.0.4.4
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 10.0.44.4/32 0.0.0.0 0 0 i （r4 始发 network的)
<R1>disp bgp rou
BGP Local router ID is 10.0.1.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 10.0.44.4/32 10.0.4.4 0 0 64513i (r1 上看出 as path 64513 ，i ， 下一条10.0.4.4 可达， 可用最佳）
<R2>disp bgp rou
BGP Local router ID is 10.0.2.2
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
i 10.0.44.4/32 10.0.4.4 0 100 0 64513i （ r2 上看到 不可用）
*>i 10.1.5.0/24 10.0.3.3 0 100 0 64514i
<R2>disp ip rou 10.0.4.4
没有任何内容，可以看出没有到达10.0.4.4 的 路由。
bgp路由的下一跳一定要通过igp迭代可以到达 ，否则不优，不可用也不会传给其他peer
解决：
- 方案1: r1 把10.0.44.4 引入IGP
- 方案2： r2 配置到10.0.4.4 的静态路由，
- r1 通过bgp 把10.0.4.4 传给r2
r2 上要去往10.0.44.4 先找 10.0.4.4
<R2>disp bgp rou
BGP Local router ID is 10.0.2.2
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 3
Network NextHop MED LocPrf PrefVal Path/Ogn*>i 10.0.4.4/32 10.0.1.1 0 100 0 i
*>i 10.0.44.4/32 10.0.4.4 0 100 0 64513i
*>i 10.1.5.0/24 10.0.3.3 0 100 0 64514i
要去往10.0.4.4 ,通过10.0.1.1 （ ibgp 方案3配置的）
要去往10.10.1.1， 通过r1-r2 之间的igp 可以到达 - 方案4 ： r1 配置 下一条属性
[R1-bgp]peer 10.0.2.2 next-hop-local
在r1 对r2 上配置 下一跳为自己
<R2>disp bgp rou
BGP Local router ID is 10.0.2.2
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 10.0.44.4/32 10.0.1.1 0 100 0 64513i
如此，r1 从ebgp r4学的 路由，下一条设置为自己于r2 建立邻居的地址 ，r2必定可用到达。
BGP 和igp 同步：
发生在从igp邻居学到bgp路由，在向ebgp发送bgp路由时
只有当bgp路由 在igp表也有时，这条bgp路由才优，所以才会传递给ebgp邻居
同步开启： R1 只有在IGP 表存在5.5.5.5/32 路由时， 才会传递给R3
华为默认关闭，且不能开启
cisco 可以开启
1 开启同步
r1#sh run | sec route
router bgp 10
bgp router-id 1.1.1.1
bgp log-neighbor-changes
neighbor 10.0.13.3 remote-as 20
neighbor 10.0.15.5 remote-as 10
!
address-family ipv4
synchronization
neighbor 10.0.13.3 activate
neighbor 10.0.15.5 activate
r1#show bgp ipv4 unicast
BGP table version is 28, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
* i 5.5.5.5/32 10.0.15.5 0 100 0 ?
2 R1配置静态路由5.5.5.5/32 指向 R5
r1#sh run | in ip route
ip route 5.5.5.5 255.255.255.255 10.0.15.5
3 5.5.5.5 已经优， 可以传递给R3
r1#sh bgp ipv4 unicast
BGP table version is 29, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
r>i 5.5.5.5/32 10.0.15.5 0 100 0 ?
r3#show bgp ipv4 unicast
BGP table version is 45, local router ID is 3.3.3.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
*> 5.5.5.5/32 10.0.13.1 0 10 ?
4 但是， R3 ping 不通5.5.5.5 ，因为R1 没有 10.0.13.0/24 路由，无法回包。。。
r1 宣告直连或 neibour r5 下一跳自己
r1(config-router-af)#do sh run | s rou
router bgp 10
bgp router-id 1.1.1.1
bgp log-neighbor-changes
neighbor 10.0.13.3 remote-as 20
neighbor 10.0.15.5 remote-as 10
!
address-family ipv4
synchronization
network 10.0.13.0 //无效，why ？
network 10.0.13.0 mask 255.255.255.0 // 有效
r1(config-router-af)#do sh bgp ipv4 un
BGP table version is 30, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
r>i 5.5.5.5/32 10.0.15.5 0 100 0 ?
*> 10.0.13.0/24 0.0.0.0 0 32768 i
r5#sh ip rou bgp
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 7 subnets, 2 masks
B 10.0.13.0/24 [200/0] via 10.0.15.1, 00:02:31
r3#ping 5.5.5.5
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 5.5.5.5, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
