基础计算机网络——网络层(Network Layer)笔记

【Forwarding & Routing 转发与路由】

1. Forwarding：process of getting through single interchange

2. Routing: process of planning trip from source node to destination node

【Virtual circuits & Datagram network 虚拟电路与数据包网络】

1. VC: behaves like telephone circuit (connection service), every router on src-dst path maintains state for each passing connections

            VC provides network-layer connection service

 

2. DN: packets between same src-dst pair may take different paths.

            DN provides network-layer connnection-less service

【Forwarding table 转发表】

1. Longest prefix matching

2. Routing protocol: RIP, OSPF, BGP 

【Subnet 子网】

1. IP address=host part+subnet part

2. device interfaces with same part of IP address

3. can physically reach each other without intervening the router

【DHCP】

Dynamic host configuration protocol: Allow host to dynamically obtain its IP address from network server when it joins network

【NAT】

Network address translation: 对外使用同一router interface的IP address，内部通过不同的Port Number识别不同的host

【IPV6】

1. 32-bit address space soon to be  completely allocated

2. header format helps speed processing and forwarding

3. header changes to facilitate QoS

4. no fragmentation allowed

【Routing Algorithm路由算法】

1. Link-state algorithm

              D(v)=min{D(v), D(w)+c(w,v)}

 2. Distance vector algorithm

              Dx(y)=min{Dv(y)+c(x,v)}

【Hierarchical routing 分级路由选择】

1. aggregate routers into regions: Autonomous System (AS)

2. routers in AS run same routing protocol

【Broadcast routing 广播路由】

1. source duplication and in-network duplication

2. using spanning tree