[Network layer] analyzes the network layer-the Internet route selection Protocol

[Network layer] Analysis of Network Layer-Internet route selection Protocol 1, ideal Routing Algorithm 1) algorithm must be correct 2) Simple computing 3) adapt to changes in traffic and network topology 4) algorithm stability 5) algorithm is fair 6) algorithm is the best: relatively reasonable 2. Hierarchical Route Selection 1) Static Route Selection: Non-adaptive route selection, simple, low overhead Dynamic Route Selection: adaptive route selection, complex, high overhead 2) Internal Gateway Protocol IGP: RIP and OSPF external gateway protocol EGP: bgp iii, RIP Routing Information Protocol (Routing Information Protocol) of the Internal Gateway Protocol 1) route table: each route is required to maintain its distance record (number of hops, A path can contain up to 15 routers) 2) RIP cannot use multiple routes between two networks at the same time. Select a path with the least routes as the current path, even if there are still faster but more routes. 3) features 1> only exchange route information with adjacent routes (current route table) 2> exchange route information at fixed intervals 4) distance Vector Algorithm 1> a rip packet is sent from an adjacent Route whose IP address is X. Change the next hop address to X. Add 1 for all distances. 2> if N is not specified in the original route table, add it. Otherwise, if the next hop address is X, the next hop address will be updated. Otherwise, if the hop count is small and the target host matches, the next hop address will be updated. Otherwise, no updates will be received in 3> 3 minutes, this route is set to 16 4> return 5). The RIP packet header is 20 bytes. It is transmitted using UDP encapsulation (port number 520). a rip can contain up to 25 routes, the maximum RIP length is 4 + 25*20 = 504 bytes. The message transmission speed is fast, and the bad message transmission speed is low. The OSPF 1 of the Internal Gateway) difference between RIP and OSPF 1> send information to all routes of the autonomous system, and use the flood method. 2> the sent information is the "link status" of all routes connected to the current route, and the link status is the router to which the router is connected. The measurement of the link indicates the cost, distance, latency, and bandwidth. The messages sent by RIP are: distance and next hop. 3> the router sends this message to all routing flood methods only when the link status changes. RIP periodically exchanges route table information regardless of link changes. 2) using the OSPF autonomous link, each route can finally establish a link status database, that is, the entire network topology. Although RIP knows the distance and next hop of all network routers, it does not know the network-wide topology. 3) OSPF uses IP datagram for sending. RIP is sent in UDP encapsulation. Benefit: the composition of a datagram is shortened without sending it in parts. 4) The first 24 bytes, RIP20 bytes. 5) Five OSPF grouping types 1> greeting group: Discover and maintain the accessibility of the Site 2> database description: summary of all link status items in the link status database sent by the site 3> Link Status Request: request to send certain link statuses 4> link status update: send a full-network update status message in flood mode 5> confirm link status: confirm link Update group 6) Send a greeting group every 10 seconds for each adjacent Route during the update process, confirm which site is reachable.