在一个PE-CE网络中，我们将重新分配BGP和IGP之间的路由，而不需要“BGP重新分配-内部”。再分配是如何运作的？

Question

在Cisco IOS/XE设备上部署PE-CE网络，如-

   +-------------+                                                                                                                                              +-------------+
   |             |.1  198.51.13.0/24                                                                                                      198.51.56.0/24     .6 |             |
   |  R1-CUST-A  +--------------------------+                                                                                        +--------------------------+  R6-CUST-A  |
   |             | E0/1                     |                                                                                        |                      E0/1|             |
   +-------------+              +----------------------------------------------------------------------------------------------------|-----------+              +-------------+
                                |           |                                                                                        |           |
                                |           |                                                                                        |           |
                                |       .3  | 3.3.3.3/32                            4.4.4.4/32                            5.5.5.5/32 | .5        |
                                |      +----+------------+                      +---------------+                       +------------+----+      |
                                |      |                 |.3   10.3.4.0/24    .4|               |.4     10.4.5.0/24   .5|                 |      |
                                |      |    R3-PE1       +----------------------+     R4-P      +-----------------------+    R5-PE2       |      |
                                |      |                 |E1/0              E1/0|               |E1/1               E1/1|                 |      |
                                |      +----+------------+                      +---------------+                       +------------+----+      |
                                |       .3  |E0/2                                                                               E0/2 | .5        |
                                |           |                                                                                        |           |
                                |           |                            SERVICE PROVIDER MPLS CORE NETWORK                          |           |
   +-------------+              +----------------------------------------------------------------------------------------------------|-----------+              +-------------+
   |             | E0/2                     |                                                                                        |                       .6 |             |
   |  R2-CUST-Z  +--------------------------+                                                                                        +--------------------------+  R7-CUST-Z  |
   |             |.2  198.51.23.0/24                                                                                                      198.51.57.0/24    E0/2|             |
   +-------------+                                                                                                                                              +-------------+

R3-PE1和R5-PE2是提供商边缘路由器。R4-P是一个提供者中间路由器.R1-CUST-A和R6-CUST-A是“客户A”路由器。R2-CUST-B和R7-CUST-B是“客户B”路由器。

在这种MPLS-L3-VPN拓扑结构中，为了提供客户路由器(如R1-CUST-A和R6-CUST-A )之间的连接，我们将在提供商边缘路由器(R3-PE1和R5-PE2)上重新分配BGP和IGP (EIGRP/OSPF)之间的路由。

在R3-PE1上的配置是-

BGP

router bgp 1                                                                                                                                                                                                                                                         
 bgp log-neighbor-changes                                                                                                                                                                                                                                            
 no bgp default ipv4-unicast                                                                                                                                                                                                                                         
 neighbor 5.5.5.5 remote-as 1                                                                                                                                                                                                                                        
 neighbor 5.5.5.5 update-source Loopback0                                                                                                                                                                                                                            
 !                                                                                                                                                                                                                                                                   
 address-family ipv4                                                                                                                                                                                                                                                 
 exit-address-family                                                                                                                                                                                                                                                 
 !                                                                                                                                                                                                                                                                   
 address-family vpnv4
  neighbor 5.5.5.5 activate
  neighbor 5.5.5.5 send-community extended
  neighbor 5.5.5.5 next-hop-self
 exit-address-family
 address-family ipv4 vrf CUST-A
  redistribute eigrp 65001
 exit-address-family
 !
 address-family ipv4 vrf CUST-Z
  redistribute eigrp 65026
 exit-address-family

EIGRP

router eigrp CUST-A                                                                                                                                                                                                                                                  
 !                                                                                                                                                                                                                                                                   
 address-family ipv4 unicast vrf CUST-A autonomous-system 65001                                                                                                                                                                                                      
  !
  topology base
   redistribute bgp 1 metric 1500 100 255 1 1500
  exit-af-topology
  network 198.51.13.3 0.0.0.0
 exit-address-family
router eigrp CUST-Z
 !
 address-family ipv4 unicast vrf CUST-Z autonomous-system 65026
  !
  topology base
   redistribute bgp 1 metric 1500 100 255 1 1500
  exit-af-topology
  network 198.51.23.3 0.0.0.0
 exit-address-family

R6-PE2 is - BGP上的组态

router bgp 1                                                                                                                                                                                                                                                         
 bgp log-neighbor-changes                                                                                                                                                                                                                                            
 no bgp default ipv4-unicast                                                                                                                                                                                                                                         
 neighbor 3.3.3.3 remote-as 1
 neighbor 3.3.3.3 update-source Loopback0
 !
 address-family ipv4
 exit-address-family
 !
 address-family vpnv4
  neighbor 3.3.3.3 activate
  neighbor 3.3.3.3 send-community extended
  neighbor 3.3.3.3 next-hop-self
 exit-address-family
 !
 address-family ipv4 vrf CUST-A
  redistribute eigrp 65001
 exit-address-family
 address-family ipv4 vrf CUST-Z
  redistribute eigrp 65026
 exit-address-family

EIGRP

router eigrp CUST-Z
 !
 address-family ipv4 unicast vrf CUST-Z autonomous-system 65026
  !
  topology base
   redistribute bgp 1 metric 1500 100 255 1 1500
  exit-af-topology
  network 198.51.57.5 0.0.0.0
 exit-address-family
router eigrp CUST-A
 !
 address-family ipv4 unicast vrf CUST-A autonomous-system 65001
  !
  topology base
   redistribute bgp 1 metric 1500 100 255 1 1500
  exit-af-topology
  network 198.51.56.5 0.0.0.0
 exit-address-family

如果您观察到，我们还没有在BGP配置下配置bgp redistribute-internal。我已经读过，命令bgp redistribute-internal需要在BGP配置下配置，以便可以将BGP路由重新分发到IGP协议上。然而，在这种情况下，即使没有命令bgp redistribute-internal重新分配BGP路由到IGP(EIGRP)工作。这怎麽可能？

Answer 1

来自：https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/command/irg-cr-book/bgp-a1.html?bookSearch=true#wp4270480859

命令默认值在Cisco IOS发布之前的版本15.1(2)S、15.2(1)T和Cisco IOS XE3.3S中，在IPv4 VRF和IPv6 VRF地址系列中，IBGP路由不被重新分配到IGP中。

我猜你有这个：

从Cisco IOS发布的15.1(2)S、15.2(1)T和Cisco IOS XE3.3S开始，在IPv4 VRF和IPv6 VRF地址家族中，IBGP路由被重新分配到IGP中。