Relationship: routing algorithm (protocol): determines the value inserted into the forwarding table inside, determines the forwarding table entries
Structure Type : Dynamic / Static Routing - internal and external gateway protocol (the BGP) - distance vector (the RIP) / link status (OSPF) routing protocol
Static, dynamic routing algorithm
static routing algorithms: simple and less overhead, but not in time to adapt to changes in network status, set by the network administrator
dynamic routing algorithms: Dynamic routing algorithm is also called adaptive routing selection algorithm, which is characterized by a more capable good adapt to changes in network status, but are complex to implement, the overhead is relatively large. Are all dynamic routing algorithm discussed below
Two routing algorithms corresponding to two routing table
(1) static routing table
static routing table is manually created by the network administrator of each path is inputted to a destination address in the routing table. When the network structure changes, the routing table can not be updated automatically. Updating the static routing table must be modified manually by the network administrator. Therefore, the static routing tables are normally only used in a small, local area network system structure does not change often happens in or troubleshooting experimental network.
(2) the dynamic routing table
large internetworks typically employ dynamic routing table. In the network system is running, the system will automatically run a dynamic routing protocol to establish a routing table. When the Internet structure changes, such as when a router fails or when a link is interrupted, the dynamic routing protocol will automatically update all the routers in the routing table. Networks of all sizes need to choose different sizes of dynamic routing protocols
Autonomous System (AS, Autonomous System): namely network (public network)
all networks within an autonomous system belongs to an administrative unit, for example, a university, a company, a government department and so on. The most important features of an autonomous system is that it have the right to choose which routing protocol (RIP / OSPF) employed within the system. Routing System (routing architecture) involves how Internet router of the regional division, management and control, routing system determines the efficiency of the Internet.
Application of the same router routing protocol (RIP / OSFP) in the same AS
gateway router (gateway router): AS is an edge, and the other is connected to the AS through physical link gateway routers directly exchange routing information of the two systems. 
Internal routing autonomous system selection algorithm
1. Distance Vector (DV, distance-victor) routing protocol RIP (Routing Information Protocol, Routing Information Protocol): talk only with their neighbors, but to the neighbors to provide their own routes to other nodes in the network ( what we know of) has the lowest cost (distance vector), and it is all his neighbors to share: the entire routing table.
2. Link status (LS, link state) routing algorithm the OSPF (the Open Shortest the Path First Open Shortest Path First): to communicate with all the nodes within the same gateway, but only provide overhead directly connected with its own link (neighboring node) is himself a neighbor to the link-state packet broadcast to all nodes within the same gateway
Some choose to add two protocols : two routing algorithms are used to determine the shortest path (minimum traffic overhead) of
link-state routing protocol, also known as Shortest Path First, it Edsger Dijkstra shortest path based on priority (SPF) algorithm, the link state protocol to collect information from all of the other routers within the defined area network or network router has information on the final one and the same link status information about each network. And each router can independently calculate their optimal path.
RIP uses B ellman - F ord algorithm to determine the shortest path, designed for small network environments, in large network environments, slow convergence, the use of regularly updated convergence will lead to slow down, resulting in inconsistent routing table can not be updated in time. Every 30 seconds, it is necessary to send the entire routing table neighboring site distance vector routing protocol, so that the routing table is updated neighboring site. Its use of "hops" (ie metric) to measure the distance of the route to the destination address. This router agreement concerned only with the world around them, only to exchange information with their neighboring routers, the range is limited to 15 hops (15 degrees), the further away, it does not care about
Inter-autonomous system routing protocol
Border Gateway Routing (BGP, broder gateway protocol) routing protocol: to achieve routing between different AS. For the AS located in the same destination, the router forwarding table is an internal routing protocol determined by the AS. For AS located outside destination, forwarding the selected AS by the protocol between AS and protocol jointly determine (RIP + BGP / OSPF + BGP )
Router according to the inter AS, the AS routing algorithm to obtain a routing table, in order to achieve complete process forward data to the destination network
to the subnet to X, are forwarded through the interface I: is calculated by the Interior Gateway Routing Protocol 1d via an interface I forwarded to the gateway router 1c to spend a minimum (shortest path, skip least)
If both X network can reach through AS3, AS2, the use of inter-AS routing protocol computing, distributed to the nearest
gateway router (the router hot potato)
Routing table entry
destination address (destination mask pre costdestination): used to identify the packet's destination IP address or destination network.
Network mask (mask), network identification address of the destination host or router resides with the destination address.
Routing IP routing table identifier added Priority (pre). How might reach a destination routes, but there is a priority to let them choose high priority routes use.
Routing overhead (cost) route to a destination when a plurality of the same priority, the minimum cost route becomes the optimal route.
Output interface (interface): Description IP packets from which interface to forward.
Next hop IP address (nexthop): indicates the next router IP address in the IP packet passes through.
