On-Demand Routing principle (ODR-On Demand Routing)

On-Demand Routing principle (ODR-On Demand Routing)
ODR uses Cisco's Discovery Protocol CDP to transmit network information between the branch router and the central router. It is only applicable to the central-branch topology environment. The vrolan may have connected several LANs, however, there is usually only one WAN connection instance that reaches the central router: basic configuration: listen tint s0/0 clock rate 64000ip add 12.1.1.1 comment shutint lo0ip add Comment RouterBenconf tint s0/1 clock rate 64000ip add 12.1.1.2 comment shutint s0/2 clock rate 64000ip add 23.1.1.2 comment shutint s0/ 3 clock rate 64000ip add 24.1.1.2 255.255.255. 0no shutint s0/4 clock rate 64000ip add Comment comment shutint lo0ip add 10.2.0.1 Comment comment tint s0/0 clock rate 64000ip add 23.1.1.1 comment shutint lo0ip add Comment comment RouterDenconf tint s0/0 clock rate 64000ip add 24.1.1.1 255.255.255.0no shutint lo0ip add 172.16.3.1 255.255.255.0exit ISPenconf tint s0/0 clock rate 64000ip add 40.1.1.1 255.2 55.255.0no shut, the other routers only have direct connection routing information. Configure the ODR on the central router RouterB. Run the command: RouterB (config) # router odr to view the route table of the remote router and the central router RouterB again: routerARouterB finds that a default route entry starting with "o" is added to RouterB, and three route entries starting with "o" are added to RouterB, here, o is short for ODR, rather than OSFP. Note: In the route table, ODR uses the lowercase letter "o". The management distance is 160. after the central router is configured with an ODR, The vro sends the prefix information of all its direct connections to the central router through the CDP protocol. ODR carries a subnet mask. Therefore, it allows different subnets in the same primary network to use a subnet mask of different lengths (VLSM ). The central router will place a default route to the branch router and add the shortest network in the ODR report to the routing table (for example, three ODR route entries in RouterB ). The central router uses the branch router's interface for sending CDP information as the next hop address to the corresponding non-direct connection network (for example, the next hop address of RouterB to the CIDR Block 172.16.1.0/24 is the s0/0 interface of router1. ). Note: ODR is not a routing protocol. The information exchanged by ODR is limited to IP prefix and default route. ODR does not report metric values. The default metric value for all routes reported by ODR is 1 hop. The route table of each branch router only contains its direct connection route entry and the ODR static default route entry from the central router. Through ODR, the central router can dynamically learn the routing information about the slave network, without the overhead required by the dynamic routing protocol. No manual configuration is required on the slave router, you can provide a default route for the vro. In the ODR environment, all routers without IP routing protocols are automatically considered as virtual routers. Because ODR relies on CDP to transmit network prefix information between the Central router and the branch router, CDP must be enabled on all links between the central router and the branch router. Run the CDP protocol command: Router (config) # cdp run CDP sends an update every 60 seconds in multicast mode. You can use the cdp timer command to modify the update cycle Show cdp interface to view CDP settings.