Redistribution and route selection protocols

We all know that the destination address can be effectively selected for data distribution when the routing selection protocol is used. So how can we allocate resources when multiple protocols coexist? Now let's talk about this issue.

I. Redistribution

1. Redistribution means that when an organization runs multiple routing protocols, it must notify the network learned by one routing protocol to the other by the selection protocol, when each endpoint can reach other points, this process is re-distributing. Although multiple routing protocols are run in the Organization, however, each internal routing protocol is considered to be the only internal routing selection protocol in AS. For example, after the VPN is redistributed to OSPF, OSPF considers that the VPN is an external routing from the external ｡

2. Select overnight routes. After redistribution, all networks will be added to the routing selection table and the routing decision is made based on the network status in the table, however, the routing selection protocol only notifies the network that has been learned through the process. When routing selection processes do not share information about the network system, it is called night routing (ships in night, SIN )｡

3. Default seed measurement values. The default seed measurement values of RIP, IGRP, and VPN are all infinite. They do not enter the route selection table unless the default value is changed; the default IS-IS metric value IS 0, but it can enter the routing table. The default OSPF metric IS two types of LSA value 20, and the routing from bgp is 1; BGP sets MED to the measurement value of IGP ｡

4. When different protocols and different paths exist, use the Management Distance and measurement value for selection:

◆ Add routes with the minimum management distance to the route table in vrouters of multiple protocols;

◆ Add a smaller metric value to the selection table for routes with multiple paths;

◆ To re-distribute a route, the route must be located in the corresponding route selection table. For example, if you want to re-distribute the RIP to the OSPF, the RIP route must be located in the RIP route table;

◆ After a route is re-distributed, the management distance is the default Management Distance from the selected protocol of the target route;

◆ The routes that are redistributed are considered as external routes. After BGP and VPN are redistributed, they are considered as external routes, and internal routes are prioritized ｡

Ii. Redistribution may cause selection loops and secondary routes. To avoid these problems, consider using default routes, passive interfaces, and distribution lists, you can use only one-to-one redistribution method, for example, RIP redistribution method, modify the measurement value, and modify the Management Distance ｡

3. Control route updates during redistribution to hide the network, prevent loops, control traffic, and ensure security. The methods include:

1. Passive interfaces. Passive interfaces do not participate in the routing process. In RIP and IGRP, they do not send updates and only listen; this type of interface does not listen, send updates, and send HELLO messages in OSPF and OSPF, so they do not establish a neighbor relationship) # passive-interface ethernet 0/0 configure the passive interface in routing process mode

2. Static Routing, Which is manually configured and applicable in small network segments, such as dial-up networks. Static Routing such as redistribution between BGP and IGP is also commonly used, for example, you can define a static supernetwork to resend a static route to BGP. Static Routing overnetworks are also used when routing protocols that support VLSM are redistributed to those that do not support VLSM ｡

3. Default route: use the default route when there is no targeted target route. If there is no default route, the group will be lost. IGP uses the default route to connect to the BGP domain, in addition, default routes are often used to connect to large networks ｡

4. The empty interface is a virtual interface and is used as the logical next hop for Static Routing, all data streams destined for the network are routed to a black hole ｡

5. distribution list. the distribution list is the access list of the application in the route selection process. It is used to determine which routes will be added to the route table or sent out through update ｡

6. route ing table. route map is a complex access list, it can be used for conditional programming. When the match condition is met, the set Modification result is executed. It has the same function as the distribution list, but the specified condition can be more complex ｡