Resend and access control list of Network Attached Routers

To set up a router, you must understand the functions of the router. This article mainly introduces two concepts of the router, re-transmission and access control list.
I. Route redistribution 1. The same routing protocol only maintains its own route. However, in some cases, for example, there are two AS instances that use the OSPF protocol, however, OSPF between AS cannot communicate with each other, so the routes between the two AS cannot communicate with each other. To enable the intercommunication between the two AS, it is necessary to run a BGP protocol between the two, through configuration, the routes calculated by OSPF in the two AS nodes can be redistributed between the two nodes through BGP. 2. BGP will advertise the routes inside the two AS nodes to the other AS nodes, and the two AS nodes will implement intercommunication. In this case, the OSPF route entries are redistributed through the BGP protocol. 3. In another case, the administrator configures a static route on a vro, but this static route can only work on this vro technology, if you want it to work on another vro, You can manually configure a static route on each vro, but this is troublesome. 4. A better way IS to re-distribute this static route through dynamic routing protocols such as OSPF or IS-IS, in this way, dynamic routing is used to re-distribute the static route to other routers, saving the trouble of manual configuration of one router.
2. Access Control List www.2cto.com 1. The ACL can work on the second or third layer of the network. Here, the ACL that works on the third layer is used as an example. The basic principle is as follows: to control access to an IP address using an ACL (such as a cut-off) on a vro, you only need to add the IP address to the ACL through configuration, and define a control action for this IP address, such as the simplest discard action. 2. When a packet passes through this router technology, the ACL is matched before the packet is forwarded. If the destination IP address of the packet exists in the ACL, perform operations based on the control actions defined in the previous ACL for the IP address, such as discarding the packet. In this way, access to this IP address can be cut off through ACL. 3. The ACL can also be used to control the source address of a message. If the ACL works on the second layer, the object controlled by the ACL changes from the third layer IP address to the second layer MAC address, according to the working principle of ACL, the ACL inserts an ACL-matching operation in the normal packet forwarding process, which will definitely affect the packet forwarding efficiency, if you need to control a large number of IP addresses, the ACL list will be longer, and the time required to match the ACL will be longer, so the forwarding efficiency of the packets will be lower, which is intolerable for some backbone routers. Today's popular science is over now. Through the above introduction, I think everyone has already understood the resending and access control list. We will introduce other router knowledge to you later.