《计算机网络——自顶向下方法与Internet特色》幻灯片Lecture43

multicast routing
Network Layer 4-9
IP Addressing: introduction
Ì IP address: 32-bit
223.1.1.1 223.1.2.1 223.1.1.2 223.1.1.4 223.1.1.3 223.1.2.9 223.1.2.2
Ì 较大的IP分组在网络中会被分
fragmentation: in: one large datagram out: 3 smaller datagrams
(“fragmented”) 割(“fragmented”)
r
一个分组就被分成了若干分 组 分组只是在最终的信宿站点 被重新“组装reassembled” 在IP 分组的首部有些位标记 用来确认和排序相关的组“ 片”
E.g. timestamp, record route taken, specify list of routers to visit.
Network Layer
4-4
IP 数据报格式
IP 协议版本号 首部长度 (bytes) 数据“类型” 余留步跳 (在经过 每个路由器后递减) ver 32 bits length service len fragment 16-bit identifier flgs offset time to upper Internet layer live checksum 32 bit source IP address 用来递交有效负荷的 上层协议 32 bit destination IP address Options (if any) E.g. 时间戳,记录路 由标记, 定义要访问 的路由器 head. type of 数据报长度 (bytes) 用于 分包/ 重装
how much overhead with TCP? Ì 20 bytes of TCP Ì 20 bytes of IP Ì = 40 bytes + app layer overhead
data (variable length, typically a TCP or UDP segment)
datagram networks Ì 4.3 What’s inside a router Ì 4.4 IP: Internet Protocol
r r r r
Internet
r r r
Datagram format IPv4 addressing ICMP IPv6
RIP OSPF BGP
Ì 4.7 Broadcast and
fragmentation: in: one large datagram out: 3 smaller datagrams
reassembly
Network Layer
4-6
IP 分包 & 重组
Ì 网络链路具有 MTU (最大传输单
位)属性 – 是有链路层最大帧的 限制决定的. r 不同类型的链路, 不同的 MTUs
223.1.3.1
223.1.3.2
223.1.1.1 = 11011111 00000001 00000001 00000001 223 1 1 1
Network Layer 4-10
IP 寻址:
IP 地址: 32-bit 用来 定义主机,路由器的接 口 Ì 接口: 连接主机,路由器 之间的物理链路
class A B C D
0 network 10 110 1110 network network multicast address host host host
1.0.0.0 to 126.255.255.255 128.0.0.0 to 191.255.255.255 192.0.0.0 to 223.255.255.255 224.0.0.0 to 239.255.255.255
identifier for host, router interface Ì interface: connection between host/router and physical link
r
223.1.3.27
r
r
router’s typically have multiple interfaces host typically has one interface IP addresses associated with each interface
Chapter 4: Network Layer
Ì 4. 1 Introduction Ì 4.2 Virtual circuit and Ì 4.5 Routing algorithms r Link state r Distance Vector r Hierarchical routing Ì 4.6 Routing in the
reassembly
r
r
Network Layer
4-7
IP Fragmentation and Reassembly
Example Ì 4000 byte datagram Ì MTU = 1500 bytes
length ID fragflag offset =4000 =x =0 =0 One large datagram becomes several smaller datagrams length ID fragflag offset =1500 =x =1 =0 length ID fragflag offset =1500 =x =1 =185 length ID fragflag offset =1040 =x =0 =370
multicast routing
Network Layer 4-1
The Internet Network layer （因特
网的网络层）
Internet network layer functions: 3 Components
Transport layer: TCP, UDP
Routing protocols •path selection •RIP, OSPF, BGP IP protocol •addressing conventions •datagram format •packet handling conrk Layer 4-12
Subnets
Ì IP address: r subnet part (high order bits) r host part (low order bits) Ì
223.1.1.1 223.1.2.1 223.1.1.2 223.1.1.4 223.1.1.3 223.1.2.9 223.1.2.2
1480 bytes in data field offset = 1480/8
Network Layer
4-8
Chapter 4: Network Layer
Ì 4. 1 Introduction Ì 4.2 Virtual circuit and Ì 4.5 Routing algorithms r Link state r Distance Vector r Hierarchical routing Ì 4.6 Routing in the
data (可变长度, 一般为一个 TCP 或UDP 数据段)
Network Layer
4-5
IP Fragmentation & Reassembly
Ì network links have MTU
(Maximum Transfer Unit) largest possible link-level frame. r different link types, different MTUs Ì large IP datagram divided (“fragmented”) within net r one datagram becomes several datagrams at source host or routers r “reassembled” only at final destination r IP header bits used to identify, order related fragments
Network layer
forwarding table
ICMP protocol •error reporting •router “signaling”
Link layer physical layer
Network Layer
4-2
Chapter 4: Network Layer
Ì 4. 1 Introduction Ì 4.2 Virtual circuit and Ì 4.5 Routing algorithms r Link state r Distance Vector r Hierarchical routing Ì 4.6 Routing in the
What’s a subnet ?
r
223.1.3.27
r
device interfaces with same subnet part of IP address can physically reach each other without intervening router
subnet
223.1.3.1 223.1.3.2
点分十进制记法 Dotted-decimal notation
223.1.1.1 = 11011111 00000001 00000001 00000001 223 1 1
Network Layer
1
4-11
IP地址
为讨论 “网络”的说法, 重新审视 IP地址:
“分类” 编址(Classful addressing):