08 BGP 华为官方文档 十一条选路原则
BGP 华为官方文档 十一条选路原则
丢弃下一跳不可达的路由
1）比较“协议首选值-pref-val”属性，数值越大越好，默认值是0，只在本设备生效，不在网络中传递
2）比较“本地优先级-local_pref”属性，数值越大越好，默认值是100
3）比较：是本地始发的路由，还是从对等体学来的路由， 本地始发的BGP路由优于从其他对等体学习到的路由，**本地始发的路由优先级：优选手动聚合>自动聚合>network>import>**从对等体学到的。
4）比较“as-path” 属性-as号越短越好
5）比较“起源属性”-指的是已什么方式注入进BGP协议的
6）比较“MED”属性，指的是一个路由器去往一个BGP路由网段的距离，类似cost
7）比较EBGP邻居优先于IBGP邻居，-EBGP路由优先级高于IBGP路由
8）比较“去往BGP路由的下一跳IP地址”的cost开销值-越小越好
—如果前面8条选路规则无法选出最优的路由，我们就可以做负载均衡了
备注：AS号一致， 在要负载均衡的那台设备上开启负载均衡功能
9）比较“cluster-list”的长度，越短越好
10）比较Router ID（Orginator_ID）的大小，越小越好
11）比较“peer 后面的IP地址的大小”，越小越好
验证 下一跳是否可达
R1
sys
Enter system view, return user view with Ctrl+Z.
[R1]bg
[R1]bgp 100
[R1-bgp]dis
[R1-bgp]display th
[R1-bgp]display this
[V200R003C00]
#
bgp 100
peer 10.10.2.2 as-number 100
peer 10.10.2.2 connect-interface LoopBack0
peer 10.10.3.3 as-number 100
peer 10.10.3.3 connect-interface LoopBack0
#
ipv4-family unicast
undo synchronization
peer 10.10.2.2 enable
peer 10.10.3.3 enable
#
return
[R1-bgp]q
[R1]dis
[R1]display bg
[R1]display bgp rou
[R1]display bgp routing-table
BGP Local router ID is 192.168.12.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 4
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 10.10.4.4/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
*>i 10.10.8.8/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
[R1]dis
[R1]display ip
[R1]display ip roi
[R1]display ip ro
[R1]display ip routing-table 10.10.4.4
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Table : Public
Summary Count : 1
Destination/Mask Proto Pre Cost Flags NextHop Interface
10.10.4.4/32 IBGP 255 0 RD 10.10.2.2 GigabitEthernet
0/0/0
[R1]dis
[R1]display bg
[R1]display bgp ro
[R1]display bgp routing-table
BGP Local router ID is 192.168.12.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 4
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 10.10.4.4/32 10.10.3.3 0 100 0 200i
i 192.168.24.4 0 100 0 200i
*>i 10.10.8.8/32 10.10.3.3 0 100 0 200i
i 192.168.24.4 0 100 0 200i
[R1]dis
[R1]display bg
[R1]display bgp ro
[R1]display bgp routing-table
BGP Local router ID is 192.168.12.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 4
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 10.10.4.4/32 10.10.3.3 0 100 0 200i
i 192.168.24.4 0 100 0 200i
*>i 10.10.8.8/32 10.10.3.3 0 100 0 200i
i 192.168.24.4 0 100 0 200i
[R1]dis
[R1]display bg
[R1]display bgp ro
[R1]display bgp routing-table
BGP Local router ID is 192.168.12.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 4
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 10.10.4.4/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
*>i 10.10.8.8/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
[R1] R2
dis
display bg
display bgp r
display bgp routing-table
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
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 10.10.4.4/32 192.168.24.4 0 0 200i
*> 10.10.8.8/32 192.168.24.4 0 0 200i
Please check whether system data has been changed, and save data in time
Configuration console time out, please press any key to log on
sys
Enter system view, return user view with Ctrl+Z.
[R2]bg
[R2]bgp 100
[R2-bgp]dis
[R2-bgp]display th
[R2-bgp]display this
[V200R003C00]
#
bgp 100
router-id 2.2.2.2
peer 10.10.1.1 as-number 100
peer 10.10.1.1 connect-interface LoopBack0
peer 192.168.24.4 as-number 200
#
ipv4-family unicast
undo synchronization
peer 10.10.1.1 enable
peer 10.10.1.1 next-hop-local
peer 192.168.24.4 enable
#
return
[R2-bgp]un
[R2-bgp]undo peer 10.10.1.1 next-hop-local
[R2-bgp]q
[R2]dis
[R2]display bg
[R2]display bgp ro
[R2]display bgp routing-table
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
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 10.10.4.4/32 192.168.24.4 0 0 200i
*> 10.10.8.8/32 192.168.24.4 0 0 200i
[R2]display bgp routing-table 10.10.4.4
BGP local router ID : 2.2.2.2
Local AS number : 100
Paths: 1 available, 1 best, 1 select
BGP routing table entry information of 10.10.4.4/32:
From: 192.168.24.4 (4.4.4.4)
Route Duration: 00h13m43s
Direct Out-interface: GigabitEthernet0/0/1
Original nexthop: 192.168.24.4
Qos information : 0x0
AS-path 200, origin igp, MED 0, pref-val 0, valid, external, best, select, acti
ve, pre 255
Advertised to such 1 peers:
10.10.1.1
[R2]display ip routing-table 10.10.4.4
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Table : Public
Summary Count : 1
Destination/Mask Proto Pre Cost Flags NextHop Interface
10.10.4.4/32 EBGP 255 0 D 192.168.24.4 GigabitEthernet
0/0/1
[R2]bg
[R2]bgp 100
[R2-bgp]peer 10.10.1.1 next-hop-local
[R2-bgp]dis
[R2-bgp]display bg
[R2-bgp]display bgp ro
[R2-bgp]display bgp routing-table
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
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 10.10.4.4/32 192.168.24.4 0 0 200i
*> 10.10.8.8/32 192.168.24.4 0 0 200i
[R2-bgp]undo peer 10.10.1.1 next-hop-local
[R2-bgp]peer 10.10.1.1 next-hop-local
[R2-bgp]dis
[R2-bgp]display bg
[R2-bgp]display bgp ro
[R2-bgp]display bgp routing-table
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
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 10.10.4.4/32 192.168.24.4 0 0 200i
*> 10.10.8.8/32 192.168.24.4 0 0 200i
[R2-bgp]display bgp routing-table
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
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 10.10.4.4/32 192.168.24.4 0 0 200i
*> 10.10.8.8/32 192.168.24.4 0 0 200i
[R2-bgp]
Please check whether system data has been changed, and save data in time
Configuration console time out, please press any key to log on
R3
The device is running!
dis
display bg
display bgp p
display bgp paths
Total Number of Routes: 0
Total Number of Paths: 0
display bgp pe
display bgp peer
BGP local router ID : 3.3.3.3
Local AS number : 100
Total number of peers : 2 Peers in established state : 2
Peer V AS MsgRcvd MsgSent OutQ Up/Down State Pre
fRcv
10.10.1.1 4 100 3 3 0 00:01:27 Established
0
192.168.34.4 4 200 3 4 0 00:01:56 Established
0
dis
display bg
display bgp ro
display bgp routing-table
BGP Local router ID is 3.3.3.3
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 1
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 10.10.4.4/32 192.168.34.4 0 0 200i
dis
display bg
display bgp r
display bgp routing-table
BGP Local router ID is 3.3.3.3
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
*> 10.10.4.4/32 192.168.34.4 0 0 200i
*> 10.10.8.8/32 192.168.34.4 0 0 200i
Please check whether system data has been changed, and save data in time
Configuration console time out, please press any key to log on
sys
Enter system view, return user view with Ctrl+Z.
[R3]bg
[R3]bgp 100
[R3-bgp]un
[R3-bgp]undo peer 10.10.1.1 next-hop-local
[R3-bgp]peer 10.10.1.1 next-hop-local
[R3-bgp]
Please check whether system data has been changed, and save data in time
Configuration console time out, please press any key to log on
R4
The device is running!
dis
display bg
display bgp pe
display bgp peer
BGP local router ID : 4.4.4.4
Local AS number : 200
Total number of peers : 2 Peers in established state : 2
Peer V AS MsgRcvd MsgSent OutQ Up/Down State Pre
fRcv
192.168.24.2 4 100 4 4 0 00:02:06 Established
0
192.168.34.3 4 100 4 4 0 00:02:06 Established
0
sys
Enter system view, return user view with Ctrl+Z.
[R4]bg
[R4]bgp 200
[R4-bgp]dis
[R4-bgp]display
[R4-bgp]display th
[R4-bgp]display this
[V200R003C00]
#
bgp 200
router-id 4.4.4.4
peer 192.168.24.2 as-number 100
peer 192.168.34.3 as-number 100
#
ipv4-family unicast
undo synchronization
peer 192.168.24.2 enable
peer 192.168.34.3 enable
#
return
[R4-bgp]ne
[R4-bgp]network 10.10.4.4 32
[R4-bgp]q
[R4]dis
[R4]display bg
[R4]display bgp pe
[R4]display bgp peer
BGP local router ID : 4.4.4.4
Local AS number : 200
Total number of peers : 2 Peers in established state : 2
Peer V AS MsgRcvd MsgSent OutQ Up/Down State Pre
fRcv
192.168.24.2 4 100 7 8 0 00:05:05 Established
0
192.168.34.3 4 100 7 8 0 00:05:05 Established
0
[R4]int
[R4]interface lo
[R4]interface LoopBack 1
[R4-LoopBack1]ip add 10.10.8.8 32
[R4-LoopBack1]q
[R4]bg
[R4]bgp 200
[R4-bgp]net
[R4-bgp]network 10.10.8.8 32
[R4-bgp]
[R4-bgp]q
[R4]dis
[R4]display bg
[R4]display bgp pe
[R4]display bgp peer
BGP local router ID : 4.4.4.4
Local AS number : 200
Total number of peers : 2 Peers in established state : 2
Peer V AS MsgRcvd MsgSent OutQ Up/Down State Pre
fRcv
192.168.24.2 4 100 10 12 0 00:08:50 Established
0
192.168.34.3 4 100 10 12 0 00:08:50 Established
0
[R4]dis
[R4]display bg
[R4]display bgp r
[R4]display bgp routing-table
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
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 10.10.4.4/32 0.0.0.0 0 0 i
*> 10.10.8.8/32 0.0.0.0 0 0 i
[R4]
Please check whether system data has been changed, and save data in time
Configuration console time out, please press any key to log on
dis
display bg
display bgp ro
display bgp routing-table
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
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 10.10.4.4/32 0.0.0.0 0 0 i
*> 10.10.8.8/32 0.0.0.0 0 0 i
Please check whether system data has been changed, and save data in time
Configuration console time out, please press any key to log on
[R4]display bgp peer
BGP local router ID : 4.4.4.4
Local AS number : 200
Total number of peers : 2 Peers in established state : 2Peer V AS MsgRcvd MsgSent OutQ Up/Down State Pre
fRcv192.168.24.2 4 100 10 12 0 00:08:50 Established 0
192.168.34.3 4 100 10 12 0 00:08:50 Established 0[R4]display bgp routing-table
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn*> 10.10.4.4/32 0.0.0.0 0 0 i
*> 10.10.8.8/32 0.0.0.0 0 0 i
R2:
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn*> 10.10.4.4/32 192.168.24.4 0 0 200i
*> 10.10.8.8/32 192.168.24.4 0 0 200i
R3:
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn*> 10.10.4.4/32 192.168.34.4 0 0 200i
*> 10.10.8.8/32 192.168.34.4 0 0 200i
R1:
Total Number of Routes: 4
Network NextHop MED LocPrf PrefVal Path/Ogn*>i 10.10.4.4/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
*>i 10.10.8.8/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
1）比较“协议首选值-pref-val”属性，数值越大越好，默认值是0，只在本设备生效，不在网络中传递。
sys
Enter system view, return user view with Ctrl+Z.
[R1]ip ip-p
[R1]ip ip-prefix ?
STRING<1-169> Specify prefix-list name
[R1]ip ip-prefix 3.3 pe
[R1]ip ip-prefix 3.3 permit 10.10.4.4 32
[R1]rou
[R1]route
[R1]route-policy 3.3 pe
[R1]route-policy 3.3 permit no
[R1]route-policy 3.3 permit node 10
Info: New Sequence of this List.
[R1-route-policy]if-match ip-prefix 3.3
[R1-route-policy]apply preferred-value 234
[R1]bgp 100
[R1-bgp]peer 10.10.3.3 route-policy 3.3 import
[R1-bgp]
refresh bgp all import
display bgp routing-table BGP Local router ID is 192.168.12.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 3
Network NextHop MED LocPrf PrefVal Path/Ogn*>i 10.10.4.4/32 10.10.3.3 0 100 234 200i
* i 10.10.2.2 0 100 0 200i
*>i 10.10.8.8/32 10.10.2.2 0 100 0 200i
display bgp routing-table 10.10.4.4 BGP local router ID : 192.168.12.1
Local AS number : 100
Paths: 2 available, 1 best, 1 select
BGP routing table entry information of 10.10.4.4/32:
From: 10.10.3.3 (3.3.3.3)
Route Duration: 00h00m48s
Relay IP Nexthop: 192.168.13.3
Relay IP Out-Interface: GigabitEthernet0/0/1
Original nexthop: 10.10.3.3
Qos information : 0x0
AS-path 200, origin igp, MED 0, localpref 100, pref-val 234, valid, internal, b
est, select, active, pre 255, IGP cost 1
Not advertised to any peer yetBGP routing table entry information of 10.10.4.4/32:
From: 10.10.2.2 (2.2.2.2)
Route Duration: 00h00m48s
Relay IP Nexthop: 192.168.12.2
Relay IP Out-Interface: GigabitEthernet0/0/0
Original nexthop: 10.10.2.2
Qos information : 0x0
AS-path 200, origin igp, MED 0, localpref 100, pref-val 0, valid, internal, pre
255, IGP cost 1, not preferred for PreVal
Not advertised to any peer yet
2）比较“本地优先级-local_pref”属性，数值越大越好，默认值是100。
[R1]route-policy 3.3 permit node 10
Info: You are overwriting this sequence.
[R1-route-policy]undo apply preferred-value
[R1]route-policy 3.3 permit node 20
Info: New Sequence of this List.
[R1-route-policy]ap
[R1-route-policy]apply lo
[R1-route-policy]apply local-preference 300
[R1-route-policy]q
[R1]bg
[R1]bgp 100
[R1-bgp]peer 10.10.3.3 route-policy 3.3 import
display bgp routing-table BGP Local router ID is 192.168.12.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 4
Network NextHop MED LocPrf PrefVal Path/Ogn*>i 10.10.4.4/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
*>i 10.10.8.8/32 10.10.3.3 0 300 0 200i
* i 10.10.2.2 0 100 0 200i
3）比较：是本地始发的路由，还是从对等体学来的路由， 本地始发的BGP路由优于从其他对等体学习到的路由，**本地始发的路由优先级：优选手动聚合>自动聚合>network>import>从对等体学到的。
4）比较“as-path” 属性-as号越短越好。
[R1-bgp]display this
[V200R003C00]
#
bgp 100
peer 10.10.2.2 as-number 100
peer 10.10.2.2 connect-interface LoopBack0
peer 10.10.3.3 as-number 100
peer 10.10.3.3 connect-interface LoopBack0
#
ipv4-family unicast
undo synchronization
peer 10.10.2.2 enable
peer 10.10.3.3 enable
#
return
[R1-bgp]display bgp routing-tableBGP Local router ID is 192.168.12.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 4
Network NextHop MED LocPrf PrefVal Path/Ogn*>i 10.10.4.4/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
*>i 10.10.8.8/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
[R1]route-policy 3.3 permit node 10
Info: You are overwriting this sequence.
[R1-route-policy]undo apply local-preference
[R1-route-policy]apply as-path 300 300 additive
[R1-bgp]peer 10.10.2.2 route-policy 3.3 import
display bgp routing-table BGP Local router ID is 192.168.12.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 4
Network NextHop MED LocPrf PrefVal Path/Ogn*>i 10.10.4.4/32 10.10.3.3 0 100 0 200i
* i 10.10.2.2 0 100 0 300 300 20
0i
*>i 10.10.8.8/32 10.10.2.2 0 300 0 200i
* i 10.10.3.3 0 100 0 200i
5）比较“起源属性”-指的是已什么方式注入进BGP协议的。
Origin : i - IGP, e - EGP, ? - incomplete
[R2-route-policy]apply origin ?
egp Remote EGP
igp Local IGP
incomplete Unknown heritage
[R2-route-policy]apply origin
Origin : i - IGP, e - EGP, ? - incomplete （优先级）
&：IGP：优先级高，通过network命令注入到BGP路由表的路由，其Origin属性为'i'。
&: e - EGP : 次优的，
&：Incomplete：优先级低，如：通过import-route注入的路由，其Origin属性为 '?'。
sys
Enter system view, return user view with Ctrl+Z.
[R2]ip ip-prefix 4.4 permit 10.10.4.4 32
[R2]route-policy 4.4 permit node 10
Info: New Sequence of this List.
[R2-route-policy]if-match ip-prefix 4.4
[R2-route-policy]apply origin incomplete
[R2-bgp]peer 10.10.1.1 route-policy 4.4 export
[R2-bgp]display bgp routing-tableBGP 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
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn*> 10.10.4.4/32 192.168.24.4 0 0 200i
*> 10.10.8.8/32 192.168.24.4 0 0 200i
[R1]bgp 100
[R1-bgp]undo peer 10.10.2.2 route-policy 3.3 import
[R1-bgp]q
[R1]undo route-policy 3.3
[R1]display bgp routing-tableBGP Local router ID is 192.168.12.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 4
Network NextHop MED LocPrf PrefVal Path/Ogn*>i 10.10.4.4/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
*>i 10.10.8.8/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
[R1]ip ip-p
[R1]ip ip-prefix 4.4 pe
[R1]ip ip-prefix 4.4 permit 10.10.4.4 32
[R1]un
[R1]undo ip ip-prefix 4.4 permit 10.10.4.4 32
display bgp routing-table BGP Local router ID is 192.168.12.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 3
Network NextHop MED LocPrf PrefVal Path/Ogn*>i 10.10.4.4/32 10.10.3.3 0 100 0 200i
* i 10.10.2.2 0 100 0 200?
*>i 10.10.8.8/32 10.10.3.3 0 100 0 200i
display bgp routing-table 10.10.4.4
BGP local router ID : 192.168.12.1
Local AS number : 100
Paths: 2 available, 1 best, 1 select
BGP routing table entry information of 10.10.4.4/32:
From: 10.10.3.3 (3.3.3.3)
Route Duration: 00h13m25s
Relay IP Nexthop: 192.168.13.3
Relay IP Out-Interface: GigabitEthernet0/0/1
Original nexthop: 10.10.3.3
Qos information : 0x0
AS-path 200, origin igp, MED 0, localpref 100, pref-val 0, valid, internal, bes
t, select, active, pre 255, IGP cost 1
Not advertised to any peer yet
BGP routing table entry information of 10.10.4.4/32:
From: 10.10.2.2 (2.2.2.2)
Route Duration: 00h01m02s
Relay IP Nexthop: 192.168.12.2
Relay IP Out-Interface: GigabitEthernet0/0/0
Original nexthop: 10.10.2.2
Qos information : 0x0
AS-path 200, origin incomplete, MED 0, localpref 100, pref-val 0, valid, intern
al, pre 255, IGP cost 1, not preferred for Origin
Not advertised to any peer yet
6）比较“MED”属性，指的是一个路由器去往一个BGP路由网段的距离，类似cost。
第一步：在R2中删除调用
[R2-bgp]undo peer 10.10.1.1 route-policy 4.4 export
第二步：验证R1的路由表：检查是否恢复默认
[R1]dis bgp routing-table
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 10.10.4.4/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
第三步：在R2中-进入路由策略，删除修改的起源属性值
[R2]route-policy 4.4 permit node 10
[R2-route-policy]undo apply origin //删除修改的起源属性值，恢复默认
[R2-route-policy]apply cost 999 //修改路由的MED属性值为999
第四步：在R2中调用路由策略
[R2]bgp 100
[R2-bgp]peer 10.10.1.1 route-policy 4.4 export
//R2在给R1发路由的时候，在出方向修改路由的MED值为999
第五步：验证结果
display bgp routing-table
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 10.10.4.4/32 10.10.3.3 0 100 0 200i
* i 10.10.2.2 999 100 0 200i 7）比较EBGP邻居优先于IBGP邻居，-EBGP路由优先级高于IBGP路由。
8）比较“去往BGP路由的下一跳IP地址”的cost开销值-越小越好。
—如果前面8条选路规则无法选出最优的路由，我们就可以做负载均衡了
备注：AS号一致， 在要负载均衡的那台设备上开启负载均衡功能
9）比较“cluster-list”的长度，越短越好。反射器
10）比较Router ID（Orginator_ID）的大小，越小越好。
R2
dis
display bg
display bgp r display bgp routing-table 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
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn*> 10.10.4.4/32 192.168.24.4 0 0 200i
*> 10.10.8.8/32 192.168.24.4 0 0 200i
[R2-bgp]router-id 8.8.8.8[R2-bgp]display bgp routing-table
BGP Local router ID is 8.8.8.8
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*> 10.10.4.4/32 192.168.24.4 0 0 200i
*> 10.10.8.8/32 192.168.24.4 0 0 200i
R1
[R1]display bgp routing-tableBGP Local router ID is 192.168.12.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 4
Network NextHop MED LocPrf PrefVal Path/Ogn*>i 10.10.4.4/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
*>i 10.10.8.8/32 10.10.2.2 0 100 0 200i
* i 10.10.3.3 0 100 0 200i
[R1]display bgp routing-table
Total Number of Routes: 4
Network NextHop MED LocPrf PrefVal Path/Ogn*>i 10.10.4.4/32 10.10.3.3 0 100 0 200i
* i 10.10.2.2 0 100 0 200i
*>i 10.10.8.8/32 10.10.3.3 0 100 0 200i
* i 10.10.2.2 0 100 0 200i
[R1]display bgp routing-table 10.10.4.4BGP local router ID : 192.168.12.1 //bgp的ip地址 192.168.12.1
Local AS number : 100 //领据号 100
Paths: 2 available, 1 best, 1 select
BGP routing table entry information of 10.10.4.4/32:
From: 10.10.3.3 (3.3.3.3)
Route Duration: 00h14m46s
Relay IP Nexthop: 192.168.13.3
Relay IP Out-Interface: GigabitEthernet0/0/1
Original nexthop: 10.10.3.3
Qos information : 0x0
AS-path 200, origin igp, MED 0, localpref 100, pref-val 0, valid, internal, bes
t, select, active, pre 255, IGP cost 1
Not advertised to any peer yetBGP routing table entry information of 10.10.4.4/32:
From: 10.10.2.2 (8.8.8.8)
Route Duration: 00h00m52s
Relay IP Nexthop: 192.168.12.2
Relay IP Out-Interface: GigabitEthernet0/0/0
Original nexthop: 10.10.2.2
Qos information : 0x0
AS-path 200, origin igp, MED 0, localpref 100, pref-val 0, valid, internal, pre
255, IGP cost 1, not preferred for router ID
Not advertised to any peer yet
11）比较“peer 后面的IP地址的大小”，越小越好
