Static and dynamic routing routes
a static route is the basic concept of
the routing system administrator manually set called static (static) routing, when the system is generally installed on the network according to preset configuration, it will not follow the future automatically changing the network topology changes. It does not take advantage of network, system resources, security; the drawback is the need to configure the network administrator to manually one by one, does not automatically make adjustments to network status changes. No redundant connection to the network, the static route may be the best choice. Static route in the routing table depends next hop is reachable routes generated in the static mode (onwer) in the routing table as static (static), as a route priority, which metric is zero.
Second, the basic configuration commands 
three, the BFD technique
1. Background
In order to protect critical applications, the network will be designed to have a certain link redundancy, network device requires a network failure can quickly detect the failure and the traffic is switched to the backup link to accelerate network convergence. At present, some link (eg POS) to achieve fast fault detection hardware detection mechanisms. However, certain links (e.g., an Ethernet link) does not have such a detection mechanism. In this case, the application must rely on its own upper layer protocol mechanisms for fault detection, the detection time of the upper layer protocols are more than one second, so the time for failure detection can not be tolerated in some applications. Some routing protocols, such as the OSPF, IS-IS although there Fast Hello function to speed up the detection rate, but the time can only reach the detection accuracy of one second, but this is only for Fast Hello protocol function, can not provide fast fault detection of other protocols
2. a technical advantage
between network devices of any type of bi-directional transfer path failure detection, including direct physical link, virtual circuit, tunnel, MPLS LSP, multihop routing paths unidirectional link and the like.
It may be a different upper layer application services, to provide consistent fast fault detection time.
Providing a detection time of less than one second, to accelerate the convergence speed of the network, reduce application downtime, improve the reliability of the network
3. technology Introduction
BFD session is established on two network devices, used to detect the bidirectional forwarding paths between network devices for applications the service. BFD itself does not neighbor discovery mechanism, but to inform their neighbors of information by the upper application services to establish a session. Periodically send BFD packets quickly after the session is established, if not received within the detection time of BFD packets is considered bidirectional forwarding path fails, the service notifies the upper application corresponding treatment.
4.BFD session establishment process
OSPF Hello mechanism discovered by their neighbors and establish a connection;
OSPF after the establishment of a new neighbor relationship, the neighbor information (including destination and source addresses, etc.) to notify the BFD; BFD session is established according to the received neighbor information.
5.BFD fault detection process flow 
is detected link failure occurs;
BFD detects a link fault, BFD neighbor session dismantle
BFD notifies the local OSPF process BFD neighbor is unreachable;
local OSPF process is interrupted OSPF neighbor relationship
four, RIP
1. Basic Concepts
RIP is a protocol based on distance vector (distance-vector) algorithm for exchanging routing information packets via UDP, the port number is 520.
RIP uses a hop count to measure the distance to the destination, the number of hops called the metric. Number of hops in the RIP, a router to its directly connected network is 0, the number of hops up to the router through a network of 1, and so on. To limit convergence time, the RIP predetermined metric is an integer between 0 ~ 15, 16 is greater than or equal to the number of hops is defined as infinite, i.e., the destination network is unreachable. Because of this limitation, RIP is not suitable for large networks.
To improve performance, prevent routing loops, RIP supports split horizon (Split Horizon) reversal and toxicity (Poison Reverse) function
2. Anti-loop mechanism
counting to infinity (Counting to infinity): The metric value 16 is defined as unreachable (infinity). When a routing loop occurs, the metric value of a route will be increased to 16, the route is considered unreachable.
Triggered update (Triggered Updates): RIP by triggering updates to avoid routing loops may be formed between a plurality of routers, but can accelerate the convergence speed. Once a route metric changes, immediately release the update message to the neighbor router, rather than waiting until the arrival of the update cycle.
Split Horizon (Split Horizon): RIP route learned from an interface is not sent back from the neighbor to the neighbor router. This not only reduces bandwidth consumption, but also to prevent routing loops.
Poison reverse (Poison Reverse): RIP learned after routing, the route metric is set to 16 (unreachable) from an interface and the interface back to the neighbor router from the original. In this way, you can delete useless information in the routing table.
3.RIP running processes
(1) to start RIP router, the router will send a request to an adjacent packet (Request message), the RIP adjacent router receives the packet, in response to the request and send the local routing table comprising response message information (response message).
(2) the router receives the response packet, update the local routing table, and sends triggered update to the neighbor router packet routing updates advertised. Adjacent router receives triggered updates, and its neighbor router sends triggered updates. After a series of triggering broadcast, each router can get and keep the updated routing information.
(3) the local router periodically transmits routing table to neighboring routers, the neighboring routers in the RIP after receiving the packets, maintenance of the local routes, selecting an optimal route, and then sent to their respective neighbors update information the updated route globally known effective. Furthermore, RIP uses the aging mechanism out routes by aging process, in order to ensure real and effective routing.
4.RIP version differences
RIP-1 is a type of routing protocol (Classful Routing Protocol), it only supports broadcasting protocol packets. RIP-1 packets do not carry mask information, it can only recognize A, B natural route segment, such Class C, so RIP-1 does not support discontinuous subnets (Discontiguous Subnet).
RIP-2 is a classless routing protocol (Classless Routing Protocol), compared with RIP-1, it has the following advantages:
support the routing tag for flexible control over routing according to the routing tag in the routing policy.
Packets masks, support route aggregation and CIDR (Classless Inter-Domain Routing, Classless Interdomain Routing).
The next hop on broadcast networks can select the optimal next hop address.
Supporting multicast routing update packets. Only RIP-2 routers can receive updates to reduce resource consumption.
Support for packet authentication protocol and provides a simple authentication and MD5 authentication to enhance security.
RIP-2 packets in two transmission: broadcast mode and multicast mode, the default send multicast packets for multicast address 224.0.0.9. When the interface runs RIP-2 broadcast mode, you can also receive RIP-1 packets.