bgp的路径属性及实验

bgp的路径属性及实验

  • bgp的路径属性分类
    • preferred-value
    • local_preference
    • AS_path
    • Origin
    • MED
    • next_hop
  • 实验

bgp的路径属性分类

preferred-value

路由的权重值,越大越优,在路由器本地配置,只影响本设备的优选,默认为0,从其他bgp对等体学到的默认为0

local_preference

用于告诉as中的路由器,哪条路径是首选,只能传递给ibgp对等体,不能传递给ebgp对等体

AS_path

是前往目标网段的路由经过的AS号列表

Origin

标识了bgp路由的起源,igp>egp>incomplete

MED

用于向外部对等体指出进入本AS的首选路径

next_hop

用于指定达到目标网段的下一跳地址

实验

bgp的路径属性及实验_第1张图片
按照实验要求,配置ip,然后配置ospf区域

<R5>
#
ospf 1 router-id 5.5.5.5 
 area 0.0.0.0 
  network 5.5.5.5 0.0.0.0 
  network 45.1.1.0 0.0.0.255 
#
<R4>
#
ospf 1 router-id 4.4.4.4 
 area 0.0.0.0 
  network 4.4.4.4 0.0.0.0 
  network 34.1.1.0 0.0.0.255 
  network 45.1.1.0 0.0.0.255 
#
<R3>
#
ospf 1 router-id 3.3.3.3 
 area 0.0.0.0 
  network 3.3.3.3 0.0.0.0 
  network 34.1.1.0 0.0.0.255 
#

然后R1,R3建立ebgp邻居,R3,R4,R5建立ibgp邻居,R5,R2建立ebgp邻居

<R1>
#
bgp 100
 router-id 1.1.1.1
 peer 13.1.1.2 as-number 300 
#
<R2>
bgp 200
 router-id 2.2.2.2
 peer 25.1.1.2 as-number 300 
<R3>
#
bgp 300
 router-id 3.3.3.3
 peer 4.4.4.4 as-number 300 
 peer 4.4.4.4 connect-interface LoopBack0
 peer 5.5.5.5 as-number 300 
 peer 5.5.5.5 connect-interface LoopBack0
 peer 13.1.1.1 as-number 100 
<R4>
#
bgp 300
 router-id 4.4.4.4
 peer 3.3.3.3 as-number 300 
 peer 3.3.3.3 connect-interface LoopBack0
 peer 5.5.5.5 as-number 300 
 peer 5.5.5.5 connect-interface LoopBack0
<R5>
#
bgp 300
 router-id 5.5.5.5
 peer 3.3.3.3 as-number 300 
 peer 3.3.3.3 connect-interface LoopBack0
 peer 4.4.4.4 as-number 300 
 peer 4.4.4.4 connect-interface LoopBack0
 peer 25.1.1.1 as-number 200 
 #
<R5> dis bgp pe

 BGP local router ID : 5.5.5.5
 Local AS number : 300
 Total number of peers : 3		  Peers in established state : 3

  Peer            V          AS  MsgRcvd  MsgSent  OutQ  Up/Down       State Pre
fRcv

  3.3.3.3         4         300      109      106     0 01:41:30 Established    
   2
  4.4.4.4         4         300      207      228     0 03:23:48 Established    
   0
  25.1.1.1        4         200       91       90     0 01:28:26 Established    
   1
<R5>
<R3>dis bgp pe

 BGP local router ID : 3.3.3.3
 Local AS number : 300
 Total number of peers : 3		  Peers in established state : 3

  Peer            V          AS  MsgRcvd  MsgSent  OutQ  Up/Down       State Pre
fRcv

  4.4.4.4         4         300      209      271     0 03:25:50 Established    
   0
  5.5.5.5         4         300      107      111     0 01:42:26 Established    
   1
  13.1.1.1        4         100      102      101     0 01:38:03 Established    
   2
<R3>

将100.1.1.1引入bgp内,在R4上查看bgp路由表,发现100从3.3.3.3走最优

<R4>dis bgp ro

 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: 3
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>i  1.1.1.1/32         3.3.3.3         0          100        0      100i
 *>i  100.1.1.0/24       3.3.3.3         0          100        0      100i
 * i                     5.5.5.5         0          100        0      200i
<R4>

我们可以修改preferred-value值来改变路径,在R4上配置

[R4-bgp]peer 5.5.5.5 preferred-value 100
[R4-bgp]dis bgp ro

 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: 3
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>i  1.1.1.1/32         3.3.3.3         0          100        0      100i
 *>i  100.1.1.0/24       5.5.5.5         0          100        100    200i
 * i                     3.3.3.3         0          100        0      100i
[R4-bgp]

也可以修改local_preference来改变路由优先,在R5上配置

[R5-bgp]default local-preference 200
[R4-bgp]dis bgp ro

 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: 3
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>i  1.1.1.1/32         3.3.3.3         0          100        0      100i
 *>i  100.1.1.0/24       5.5.5.5         0          200        0      200i
 * i                     3.3.3.3         0          100        0      100i
[R4-bgp]

可以修改AS_path,来改变路由优先,先写一条acl

#
acl number 2000  
 rule 5 permit source 100.1.1.0 0.0.0.255 
[R3]route-policy 1 permit node  10
Info: New Sequence of this List.
[R3-route-policy]if-match  acl 2000
[R3-route-policy]apply as-path 20 additive 
[R3-route-policy]q
[R3]route-policy 1 pe no 20
Info: New Sequence of this List.
[R3-route-policy]bgp 300
[R3-bgp]peer 4.4.4.4 route-policy 1 export 

在R4上看

[R4-bgp]dis bgp ro

 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: 3
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>i  1.1.1.1/32         3.3.3.3         0          100        0      100i
 *>i  100.1.1.0/24       5.5.5.5         0          100        0      200i
 * i                     3.3.3.3         0          100        0      20 100i
[R4-bgp]

可以修改Origin来改变路由选择,在R1上引入直连

[R1-bgp]im direct 
[R4-bgp]dis bgp ro

 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: 3
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>i  1.1.1.1/32         3.3.3.3         0          100        0      100i
 *>i  100.1.1.0/24       5.5.5.5         0          100        0      200i
 * i                     3.3.3.3         0          100        0      100?
[R4-bgp]

可以看到igp优于incomplete

可以修改med来改变路径选择,在R3上配置

[R3]route-policy 1 permit node  10
Info: New Sequence of this List.
[R3-route-policy]apply cost 100
[R3-route-policy]q
[R3]route-policy 1 permit node 20
Info: New Sequence of this List.
[R3-route-policy]q
[R3]bgp 300
[R3-bgp]peer 13.1.1.1 route-policy 1 import 

注意,要比较不同的as的路由,使用compare-different-as-med开启不同as之间的比较
可以看到R4上5.5.5.5的路径优先

[R4-bgp]dis bgp ro

 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: 3
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>i  1.1.1.1/32         3.3.3.3         100        100        0      100i
 *>i  100.1.1.0/24       5.5.5.5         0          100        0      200i
 * i                     3.3.3.3         100        100        0      100i
[R4-bgp]

实验总结:bgp的路径属性有很多种,有些属性改变可以改变bgp的路径选择,选择顺序是
bgp的路径属性及实验_第2张图片

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