BGP选路原则彻底理解！（下）
依次选择从EBGP、联盟、IBGP学来的路由
配置修改下，
R2R4 AS65002 ，R3 65003
[R1]dis cu conf bgp
#
bgp 100
network 1.1.1.1 255.255.255.255
undo synchronization
peer 12.12.12.2 as-number 200
peer 13.13.13.3 as-number 200
#
Return
[R2-bgp]dis th
#
bgp 65002
confederation id 200
confederation peer-as 65003
network 2.2.2.2 255.255.255.255
undo synchronization
peer 12.12.12.1 as-number 100
peer 4.4.4.4 as-number 65002
peer 4.4.4.4 next-hop-local
peer 4.4.4.4 connect-interface LoopBack0
#
Return
[R3-bgp]dis th
#
bgp 65003
confederation id 200
confederation peer-as 65002
network 3.3.3.3 255.255.255.255
undo synchronization
peer 4.4.4.4 as-number 65002
peer 13.13.13.1 as-number 100
peer 4.4.4.4 next-hop-local
peer 4.4.4.4 connect-interface LoopBack0
#
Return
[R4]dis cu conf bgp
[R4]dis cu conf bgp
#
bgp 65002
confederation id 200
confederation peer-as 65003
network 4.4.4.4 255.255.255.255
undo synchronization
peer 2.2.2.2 as-number 65002
peer 3.3.3.3 as-number 65003
peer 2.2.2.2 connect-interface LoopBack0
peer 3.3.3.3 connect-interface LoopBack0
#
Return
查看r2r4的bgp路由表
[R4]dis bgp routing-table
Total Number of Routes: 5
BGP Local router ID is 4.4.4.4
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
*>i 1.1.1.1/32 3.3.3.3 0 100 0 (65003)
100i
* i 2.2.2.2 0 100 0 100i
i 2.2.2.2/32 2.2.2.2 0 100 0 i
i 3.3.3.3/32 3.3.3.3 0 100 0 (65003)i
*> 4.4.4.4/32 0.0.0.0 0 0 i
[R2-bgp]dis bgp routing-table
Total Number of Routes: 4
BGP Local router ID is 2.2.2.2
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
*> 1.1.1.1/32 12.12.12.1 0 0 100i
* i 3.3.3.3 0 100 0 (65003)
100i
*> 2.2.2.2/32 0.0.0.0 0 0 i
i 4.4.4.4/32 4.4.4.4 0 100 0 i
上述现象可知ebgp>联盟>ibgp
优选CLUSTER_LIST长度最短的路由；
优选ORIGINATOR_ID最小的路由；
这两条原则我本想还用原来的拓扑来演示，可是遗憾没找到解决方法，重新画了一个，大家将就看
R2R3R4做反射
基本配置：
[R1-bgp]dis th
#
bgp 100
router-id 1.1.1.1
dampening
network 1.1.1.1 255.255.255.255
import-route direct
undo synchronization
peer 12.12.12.2 as-number 100
peer 13.13.13.3 as-number 100
#
Return
[R2-bgp]dis th
#
bgp 100
router-id 2.2.2.2
network 2.2.2.2 255.255.255.255
import-route direct
undo synchronization
peer 12.12.12.1 as-number 100
peer 24.24.24.4 as-number 100
peer 12.12.12.1 reflect-client
#
[R3-bgp]dis th
#
bgp 100
router-id 3.3.3.3
network 3.3.3.3 255.255.255.255
import-route direct
undo synchronization
peer 13.13.13.1 as-number 100
peer 35.35.35.5 as-number 100
peer 13.13.13.1 reflect-client
#
Return
[R4-bgp]dis th
#
bgp 100
router-id 4.4.4.4
network 4.4.4.4 255.255.255.255
import-route direct
undo synchronization
peer 24.24.24.2 as-number 100
peer 45.45.45.5 as-number 100
peer 24.24.24.2 reflect-client
#
Return
[R5-bgp]dis th
#
bgp 100
router-id 5.5.5.5
network 5.5.5.5 255.255.255.255
import-route direct
undo synchronization
peer 45.45.45.4 as-number 100
peer 35.35.35.3 as-number 100
#
Return
查看R1的bgp路由表
*>i 5.5.5.5/32 35.35.35.5 0 100 0 i
* i 45.45.45.5 0 100 0 i
为什么优选35.35.35.5的路由呢？
[R1-bgp]dis bgp routing-table 5.5.5.5
BGP local router ID : 1.1.1.1
Local AS number : 100
Paths: 2 available, 1 best
BGP routing table entry information of 5.5.5.5/32:
From : 13.13.13.3 (3.3.3.3)
Relay Nexthop : 13.13.13.3
Original nexthop: 35.35.35.5
AS-path : (null)
Origin : igp
Attribute value : MED 0, localpref 100, pref-val 0, pre 255
State : valid, internal, best,
Originator : 5.5.5.5
Cluster list : 3.3.3.3
Not advertised to any peers yet
BGP routing table entry information of 5.5.5.5/32:
From : 12.12.12.2 (2.2.2.2)
Relay Nexthop : 12.12.12.2
Original nexthop: 45.45.45.5
AS-path : (null)
Origin : igp
Attribute value : MED 0, localpref 100, pref-val 0, pre 255
State : valid, internal,
Originator : 5.5.5.5
Cluster list : 2.2.2.2, 4.4.4.4
Not advertised to any peers yet
因为 来自R3的路由5.5.5.5的Cluster list值比较短！
下面是
优选ORIGINATOR_ID最小的路由
去掉
R4上的反射配置！
查看R1的45.45.45.0bgp路由表
*>i 45.45.45.0/24 24.24.24.4 0 100 0 ?
* i 35.35.35.5 0 100 0 ?
[R1-bgp]dis bgp routing-table 45.45.45.0
BGP local router ID : 1.1.1.1
Local AS number : 100
Paths: 2 available, 1 best
BGP routing table entry information of 45.45.45.0/24:
From : 12.12.12.2 (2.2.2.2)
Relay Nexthop : 12.12.12.2
Original nexthop: 24.24.24.4
AS-path : (null)
Origin : incomplete
Attribute value : MED 0, localpref 100, pref-val 0, pre 255
State : valid, internal, best,
Originator : 4.4.4.4
Cluster list : 2.2.2.2
Not advertised to any peers yet
BGP routing table entry information of 45.45.45.0/24:
From : 13.13.13.3 (3.3.3.3)
Relay Nexthop : 13.13.13.3
Original nexthop: 35.35.35.5
AS-path : (null)
Origin : incomplete
Attribute value : MED 0, localpref 100, pref-val 0, pre 255
State : valid, internal,
Originator : 5.5.5.5
Cluster list : 3.3.3.3
Not advertised to any peers yet
ORIGINATOR_ID
这个值默认选
router id