08 BGP 华为官方文档十一条选路原则

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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


<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 100peer 10.10.2.2 as-number 100 peer 10.10.2.2 connect-interface LoopBack0peer 10.10.3.3 as-number 100 peer 10.10.3.3 connect-interface LoopBack0#ipv4-family unicastundo synchronizationpeer 10.10.2.2 enablepeer 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 - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 4Network            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         Interface10.10.4.4/32  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 - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 4Network            NextHop        MED        LocPrf    PrefVal Path/Ogn*>i  10.10.4.4/32       10.10.3.3       0          100        0      200ii                     192.168.24.4    0          100        0      200i*>i  10.10.8.8/32       10.10.3.3       0          100        0      200ii                     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 - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 4Network            NextHop        MED        LocPrf    PrefVal Path/Ogn*>i  10.10.4.4/32       10.10.3.3       0          100        0      200ii                     192.168.24.4    0          100        0      200i*>i  10.10.8.8/32       10.10.3.3       0          100        0      200ii                     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 - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 4Network            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


<R2>dis	
<R2>display  bg	
<R2>display  bgp  r	
<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 - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 2Network            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>Please check whether system data has been changed, and save data in timeConfiguration console time out, please press any key to log on<R2>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 100router-id 2.2.2.2peer 10.10.1.1 as-number 100 peer 10.10.1.1 connect-interface LoopBack0peer 192.168.24.4 as-number 200 #ipv4-family unicastundo synchronizationpeer 10.10.1.1 enablepeer 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 - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 2Network            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 10.10.4.4BGP local router ID : 2.2.2.2Local AS number : 100Paths:   1 available, 1 best, 1 selectBGP 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: GigabitEthernet0/0/1Original nexthop: 192.168.24.4Qos information : 0x0AS-path 200, origin igp, MED 0, pref-val 0, valid, external, best, select, acti
ve, pre 255Advertised 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         Interface10.10.4.4/32  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 - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 2Network            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 - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 2Network            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-tableBGP Local router ID is 2.2.2.2 Status codes: * - valid, > - best, d - damped,h - history,  i - internal, s - suppressed, S - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 2Network            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 timeConfiguration console time out, please press any key to log on

R3

The device is running!<R3>dis	
<R3>display  bg	
<R3>display  bgp  p	
<R3>display  bgp  pathsTotal Number of Routes: 0Total Number of Paths: 0
<R3>display bgp pe	
<R3>display bgp peer BGP local router ID : 3.3.3.3Local AS number : 100Total number of peers : 2		  Peers in established state : 2Peer            V          AS  MsgRcvd  MsgSent  OutQ  Up/Down       State Pre
fRcv10.10.1.1       4         100        3        3     0 00:01:27 Established    0192.168.34.4    4         200        3        4     0 00:01:56 Established    0
<R3>dis	
<R3>display  bg	
<R3>display  bgp  ro	
<R3>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 - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 1Network            NextHop        MED        LocPrf    PrefVal Path/Ogn*>   10.10.4.4/32       192.168.34.4    0                     0      200i
<R3>dis	
<R3>display  bg	
<R3>display  bgp  r	
<R3>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 - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 2Network            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
<R3>Please check whether system data has been changed, and save data in timeConfiguration console time out, please press any key to log on<R3>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 timeConfiguration console time out, please press any key to log on

R4

The device is running!<R4>dis	
<R4>display  bg	
<R4>display  bgp  pe	
<R4>display  bgp  peer BGP local router ID : 4.4.4.4Local AS number : 200Total number of peers : 2		  Peers in established state : 2Peer            V          AS  MsgRcvd  MsgSent  OutQ  Up/Down       State Pre
fRcv192.168.24.2    4         100        4        4     0 00:02:06 Established    0192.168.34.3    4         100        4        4     0 00:02:06 Established    0
<R4>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 200router-id 4.4.4.4peer 192.168.24.2 as-number 100 peer 192.168.34.3 as-number 100 #ipv4-family unicastundo synchronizationpeer 192.168.24.2 enablepeer 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 : 4.4.4.4Local AS number : 200Total number of peers : 2		  Peers in established state : 2Peer            V          AS  MsgRcvd  MsgSent  OutQ  Up/Down       State Pre
fRcv192.168.24.2    4         100        7        8     0 00:05:05 Established    0192.168.34.3    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 : 4.4.4.4Local AS number : 200Total 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    0192.168.34.3    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 - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 2Network            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 timeConfiguration console time out, please press any key to log on<R4>
<R4>
<R4>
<R4>dis	
<R4>display  bg	
<R4>display  bgp  ro	
<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 - StaleOrigin : i - IGP, e - EGP, ? - incompleteTotal Number of Routes: 2Network            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 timeConfiguration 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 : 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]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。

<R1>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]
<R1>refresh bgp all import
<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: 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
<R1>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 yet

BGP 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
<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 10.10.3.3 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-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]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
<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 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
<R1>

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 '?'。

<R2>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-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

[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-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]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
<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: 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

<R1>display bgp routing-table 10.10.4.4BGP local router ID : 192.168.12.1Local AS number : 100Paths:   2 available, 1 best, 1 selectBGP 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: 192.168.13.3Relay IP Out-Interface: GigabitEthernet0/0/1Original nexthop: 10.10.3.3Qos information : 0x0AS-path 200, origin igp, MED 0, localpref 100, pref-val 0, valid, internal, bes
t, select, active, pre 255, IGP cost 1Not 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: 00h01m02s  Relay IP Nexthop: 192.168.12.2Relay IP Out-Interface: GigabitEthernet0/0/0Original nexthop: 10.10.2.2Qos information : 0x0AS-path 200, origin incomplete, MED 0, localpref 100, pref-val 0, valid, intern
al, pre 255, IGP cost 1, not preferred for OriginNot advertised to any peer yet<R1>

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: 2Network            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
<R1>display bgp routing-table Total Number of Routes: 2Network            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

<R2>dis
<R2>display bg
<R2>display bgp r
<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-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-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]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 10.10.4.4

BGP 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 yet

BGP 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