IBGP水平分割――路由反射器

IBGP水平分割：从IBGP学习到的路由绝不对再传播给其它的IBGP邻居（可以传给EBGP邻居）。IGP中的RIP、IGRP是基于端口的水平分割；而IBGP是基于邻居的水平分割。

IBGP水平分割主要是为了防止在AS内部产生路由环路！（而对于EBGP的水平分割主要有AS-PATH控制！）

解决办法：1、full mesh（大型的网络中不现实）

          2、路由反射器

          3、联邦

这里我们这里就详细的讨论路由反射器。

1、路由反射器：C/S模型，在一个AS内，其中一台路由器作为路由反射器RR(Route Reflector)，其它路由器做为客户机(Client)。客户机与路由反射器之间建立IBGP连接。路由反射器和它的客户机组成一个集群(Cluster)。

2、工作原理：

　　1)从非客户机IBGP对等体学到的路由，发布给此RR的所有客户机。

　　2)从客户机学到的路由，发布给此RR的所有非客户机和其他客户机

　　3)从EBGP对等体学到的路由，发布给所有的非客户机和客户机。

　　RR只需要在反射器上配置，客户机不需要知道自己是客户机。（所以在选RR的时候要根据拓扑选择最合适的路由器，不然达不到效果！！）

3、路由反射器的两个可选非传递属性：Originator_ID和Cluster_List。都是为了防止环路的。

ORIGINATOR_ID是本地AS中路由发起方的Route ID，如果发起方发现接收到的路由的Originator_ID是自己Route ID，就知道出现了路由环路，因而忽略该路由

CLUSTER_LIST是由一串由路由传递所经过的路由反射簇（cluster）ID，如果RR发现其本地簇ID在其所接收到得路由的Cluster_list中，那么就知道出现了环路。

实验拓扑：

R1：

interface Loopback100  ip address 100.1.1.1 255.255.255.0 ! interface FastEthernet0/0  ip address 11.1.1.1 255.255.255.0 ! router bgp 100  no synchronization  bgp log-neighbor-changes  network 100.1.1.0 mask 255.255.255.0  neighbor 11.1.1.2 remote-as 200 !

 

R2:

interface Loopback1  ip address 2.2.2.2 255.255.255.0 ! interface FastEthernet0/0  ip address 12.1.1.1 255.255.255.0 ! interface FastEthernet1/0  ip address 11.1.1.2 255.255.255.0 ! router rip  version 2  network 2.0.0.0  network 12.0.0.0  no auto-summary ! router bgp 200  no synchronization  bgp router-id 2.2.2.2  bgp log-neighbor-changes  neighbor 3.3.3.3 remote-as 200  neighbor 3.3.3.3 update-source Loopback1  neighbor 3.3.3.3 next-hop-self  neighbor 11.1.1.1 remote-as 100 !

 

R3:

interface Loopback1  ip address 3.3.3.3 255.255.255.0 ! interface FastEthernet0/0  ip address 13.1.1.1 255.255.255.0 ! interface FastEthernet1/0  ip address 12.1.1.2 255.255.255.0  duplex half ! router rip  version 2  network 3.0.0.0  network 12.0.0.0  network 13.0.0.0  no auto-summary ! router bgp 200  no synchronization  bgp router-id 3.3.3.3  bgp log-neighbor-changes  neighbor 2.2.2.2 remote-as 200  neighbor 2.2.2.2 update-source Loopback1  neighbor 4.4.4.4 remote-as 200  neighbor 4.4.4.4 update-source Loopback1 !

 

R4:

interface Loopback1  ip address 4.4.4.4 255.255.255.0 ! interface FastEthernet0/0  ip address 14.1.1.1 255.255.255.0  duplex half ! interface FastEthernet1/0  ip address 13.1.1.2 255.255.255.0  duplex half ! router rip  version 2  network 4.0.0.0  network 13.0.0.0  no auto-summary ! router bgp 200  no synchronization  bgp router-id 4.4.4.4  bgp log-neighbor-changes  neighbor 3.3.3.3 remote-as 200  neighbor 3.3.3.3 update-source Loopback1  neighbor 3.3.3.3 next-hop-self  neighbor 14.1.1.2 remote-as 300

 

R5:

interface Loopback30  ip address 30.1.1.1 255.255.255.0 ! router bgp 300  no synchronization  bgp log-neighbor-changes  network 30.1.1.0 mask 255.255.255.0  neighbor 14.1.1.1 remote-as 200 !

 

R3#sh ip bg BGP table version is 9, local router ID is 3.3.3.3 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete    Network          Next Hop            Metric LocPrf Weight Path *>i30.1.1.0/24      4.4.4.4                  0    100      0 300 i *>i100.1.1.0/24     2.2.2.2                  0    100      0 100 i

 

R2#sho ip bg BGP table version is 8, local router ID is 2.2.2.2 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete    Network          Next Hop            Metric LocPrf Weight Path *> 100.1.1.0/24     11.1.1.1                 0             0 100 i

 

R4#sh ip bg  BGP table version is 6, local router ID is 4.4.4.4 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete    Network          Next Hop            Metric LocPrf Weight Path *> 30.1.1.0/24      14.1.1.2                 0             0 300 i

由上看到R2和R4都将学到了路由传给了R3，但是由于IBGP水平分割问题，R3不会转发给其邻居。

将R3配做路由反射器：

R3(config)#router b 200 R3(config-router)#neighbor 2.2.2.2 route-reflector-client 03:21:59: %BGP-5-ADJCHANGE: neighbor 2.2.2.2 Down RR client config change R3(config-router)#neighbor 4.4.4.4 route-reflector-client 03:22:15: %BGP-5-ADJCHANGE: neighbor 4.4.4.4 Down RR client config change R3(config-router)# 03:22:25: %BGP-5-ADJCHANGE: neighbor 2.2.2.2 Up R3(config-router)# 03:22:41: %BGP-5-ADJCHANGE: neighbor 4.4.4.4 Up

可以看到R3与R2和R4重新建立了邻居关系。

R3#sho ip bg neighbors BGP neighbor is 2.2.2.2,  remote AS 200, internal link   BGP version 4, remote router ID 2.2.2.2   BGP state = Established, up for 00:02:57   Last read 00:00:56, hold time is 180, keepalive interval is 60 seconds   Neighbor capabilities:     Route refresh: advertised and received(old & new)     Address family IPv4 Unicast: advertised and received   Message statistics:     InQ depth is 0     OutQ depth is 0                          Sent       Rcvd     Opens:                  8          8     Notifications:          0          0     Updates:               10         12     Keepalives:           300        300     Route Refresh:          2          1     Total:                320        321   Default minimum time between advertisement runs is 5 seconds    For address family: IPv4 Unicast   BGP table version 29, neighbor version 29   Index 1, Offset 0, Mask 0x2   Route-Reflector Client  //在RR可以看到R2和R4是client                                  Sent       Rcvd   Prefix activity:               ----       ----     Prefixes Current:               1          1 (Consumes 36 bytes)     Prefixes Total:                 1          1     Implicit Withdraw:              0          0     Explicit Withdraw:              0          0     Used as bestpath:             n/a          1     Used as multipath:            n/a          0   ! ! SRTT: 197 ms, RTTO: 984 ms, RTV: 787 ms, KRTT: 0 ms minRTT: 4 ms, maxRTT: 300 ms, ACK hold: 200 ms Flags: higher precedence, nagle           Datagrams (max data segment is 536 bytes): Rcvd: 9 (out of order: 0), with data: 7, total data bytes: 199 Sent: 13 (retransmit: 0, fastretransmit: 0), with data: 7, total data bytes: 213           BGP neighbor is 4.4.4.4,  remote AS 200, internal link   BGP version 4, remote router ID 4.4.4.4   BGP state = Established, up for 00:02:43   Last read 00:00:43, hold time is 180, keepalive interval is 60 seconds   Neighbor capabilities:     Route refresh: advertised and received(old & new)     Address family IPv4 Unicast: advertised and received   Message statistics:     InQ depth is 0     OutQ depth is 0                          Sent       Rcvd     Opens:                  8          8     Notifications:          0          0     Updates:                9         14     Keepalives:           300        300     Route Refresh:          2          3     Total:                319        325   Default minimum time between advertisement runs is 5 seconds    For address family: IPv4 Unicast   BGP table version 29, neighbor version 29   Index 2, Offset 0, Mask 0x4   Route-Reflector Client                                  Sent       Rcvd   Prefix activity:               ----       ----     Prefixes Current:               1          1 (Consumes 36 bytes)     Prefixes Total:                 1          1     Implicit Withdraw:              0          0     Explicit Withdraw:              0          0     Used as bestpath:             n/a          1     Used as multipath:            n/a          0 ! ! ! iss: 3706214856  snduna: 3706215070  sndnxt: 3706215070     sndwnd:  16171 irs:  807270701  rcvnxt:  807270901  rcvwnd:      16185  delrcvwnd:    199   SRTT: 186 ms, RTTO: 1079 ms, RTV: 893 ms, KRTT: 0 ms minRTT: 4 ms, maxRTT: 352 ms, ACK hold: 200 ms Flags: higher precedence, nagle           Datagrams (max data segment is 536 bytes): Rcvd: 7 (out of order: 0), with data: 5, total data bytes: 199 Sent: 10 (retransmit: 0, fastretransmit: 0), with data: 6, total data bytes: 21