I. Overview:Bidirectional redistribution is generally required when route redistribution is performed. However, if redundant paths exist, bidirectional dual-point routing redistribution is performed, there may be routing loops or sub-optimal routing problems. For external routing entries of the VPN gateway, you can only use route-map to modify metric. Instead, you cannot use the distance command to pick out routes and use the ACL to modify the Management distance, if the problem is solved by using VPN, you can only modify metric. Refer to the following link: 650) this. width = 650; "src =" http://333234.blog.51cto.com/e/u/themes/default/images/spacer.gif "style =" url (/e/u/lang/zh-cn/images/localimage.png) no-repeat center; border: 1px solid # ddd "/> http://www.groupstudy.com/archives/ccielab/200309/msg00018.html
You can change the distance of Kerberos on a per prefix basis, but only for internal VPN routes.
Ii. Test topology:650) this. width = 650; "src =" http://www.bkjia.com/uploads/allimg/131227/05091961P-1.jpg "title =" vintage. JPG "/>
Iii. Problems arising from bidirectional dual-point redistribution and solutions:
A. External route 5.5.5.0/24--- Introduce the 5.5.5.0/24 of the OSPF 500 to the MongoDB 100 as an external route, and the Management Distance learned by SW1 is 170. If R1 learns the route first, then, it will re-distribute the route to OSPF in the form of OE2, so R4 can learn the route through OSPF and OSPF, because the OSPF management distance is 110, because the Management Distance of the external route is 170 smaller than that of the VPN gateway, the routes that reach the v5.5.0/24 are considered to be OSPF, rather than the left-side of the VPN gateway. ---- Then R4 will re-distribute the OSPF route to the OSPF route so that SW1 can learn two equivalent routes to 5.5.5.0/24, one for R4 and the other for R5.
Solution 1:
Solve this problem by adjusting distance① Use an ACL to capture all external routes of the network. Then, use distance to specify the router-id and ACL in OSPF between R3 and R4, and set the Management distance to greater than 170.
Solution example:
R3:Access-list 5 permit 5.5.5.0 0.0.255router ospf 1 router-id 3.3.3.3 distance 171 4.4.4.4 0.0.0.0 5
R4:Access-list 5 permit 5.5.5.0 0.0.255router ospf 1 router-id 4.4.4.4 distance 171 3.3.3.3 0.0.0.0 5 ② because it is an external routing of the network, the distance, IP Source address, and ACL cannot be used to set the Management distance of the specified route. Adjusting the Management distance of the external routing of the VPN gateway can solve the problem of sub-optimal routing of v5.5.0/24, however, a new sub-optimal route is generated, which is not recommended.
Solution 2: tag through route redistribution① When each distribution point is redistributed to OSPF, It is tagged. Another redistribution point uses route-map to discard all the tagged routes. ---- This configuration can solve the problem of sub-optimal paths and routing loops. However, when a distribution point and the neighbor of the VPN gateway have a problem, there is no redundant path, therefore, GNS adopts solution 1.
Solution example:
R3 and R4:Route-map tag10 deny 10
Match tag 10
Route-map tag10 permit 20 router ospf 1 redistribute VPN 100 subnets tag 10 distribute-list route-map tag10 in
B. distribution point: the direct connection route advertised by OSPF or
Re-distributed direct connection route---- For example, if R3's direct connection route 3.3.3.0/24 is declared as OSPF, it will publish this route to OSPF and redistribute this OSPF route to OSPF, when R4 learns this route through OSPF, it will also re-distribute it to the OSPF, so that SW1 has two equivalent paths to 3.3.3.0/24, one to R3 and the other to R4, obviously, the path that follows R4 is a sub-optimal path. ---- If the direct connection route of the distribution point is not declared in both the network and OSPF, but enters the network in the redistribution mode, if both the network and OSPF are declared, the two equal-cost routes of the Network B will also appear, take two distribution points.
Solution:
Solve this problem by adjusting metric① Through ACL, each redistribution point can capture the direct connection route or re-distributed route of another distribution point, and use route-map to modify the metric value in the out direction of the connection of the re-distribution point.
Solution example:
R3:Access-list 4 permit 4.4.4.0 0.0.255route-map 4 addmetric permit 10
Match ip address 4
Set metric 361120
Route-map 4 addmetric permit 20 router image100
Distribute-list route-map 4 addmetric out Ethernet0/0
R4:Access-list 3 permit 3.3.3.0 0.0.255route-map 3 addmetric permit 10
Match ip address 3
Set metric 361120
Route-map 3 addmetric permit 20 router image100
Distribute-list route-map 3 addmetric out Ethernet0/0
4. GNS3 topology and configuration file:
---- See uploaded attachments.
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