计算机网络原理(英文版)课件Chapter4new.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Chapter 4: Network Layer 4. 1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What’s inside a router 4.4 IP: Internet Protocol Datagram format IPv4 addressing ICMP IPv6 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4.6 Routing in the Internet RIP OSPF BGP OSPF “advanced” features (not in RIP) Uses Link State algorithm Carried in OSPF messages directly over IP Security: all OSPF messages authenticated (to prevent malicious intrusion) Multiple same-cost paths allowed For each link, multiple cost metrics for different TOS Integrated uni- and multicast support: Multicast OSPF (MOSPF) uses same data base as OSPF Hierarchical OSPF in large domains. Hierarchical OSPF Back bone area internal router area internal router area internal router area border router (区域边缘路由器） boundary router （边界路由器） To other AS AS To other AS Hierarchical OSPF Two-level hierarchy: local area, backbone. Link-state advertisements only in area each nodes has detailed area topology; only know direction (shortest path) to nets in other areas. Area border（边缘） routers: “summarize” distances to nets in own area, advertise to other Area Border routers. Backbone routers: run OSPF routing limited to backbone. Boundary（边界） routers: connect to other AS’s. Chapter 4: Network Layer 4. 1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What’s inside a router 4.4 IP: Internet Protocol Datagram format IPv4 addressing ICMP IPv6 4.5 Routing algorithms Link state Distance Vector Hierarchical routing 4.6 Routing in the Internet RIP OSPF BGP BGP is the de facto standard Distance Vector algorithm? Path vector algorithm protocol: an extension of Distance Vector Each Border Gateway broadcasts to neighbors (peers) the entire path (ie, sequence of ASes) to destination (no cost info is sent) BGP plays a central role in internet. BGP can be used inside an AS and is called Internal BGP