1. 不同设备聚合带宽

image.png

1. 由交换机聚合带宽性质得到9100=900M
1. 集线器是一个单冲突域,每个系内设备都会冲突,最大吞吐量100,因此1003+200=500M
1. 同二,最大只有100M,系内设备和三个系与两台服务器间都会冲突

2. DHCP四次交互的MAC和IP变化

如图new host为了从DHCP获取IP192.168.1.4,其中pkt的IP和MAC情况如何?(ARP为空)
image.png

src MAC dest MAC src IP dest IP yiaddr
66-66-66-66-66-66 FF-FF-FF-FF-FF-FF 0.0.0.0 255.255.255.255 0.0.0.0
33-33-33-33-33-33 FF-FF-FF-FF-FF-FF 192.168.1.1 255.255.255.255 192.168.1.4
66-66-66-66-66-66 FF-FF-FF-FF-FF-FF 0.0.0.0 255.255.255.255 192.168.1.4
33-33-33-33-33-33 FF-FF-FF-FF-FF-FF 192.168.1.1 255.255.255.255 192.168.1.4

**注意IP广播时,即IP中主机位都是1时,MAC一定广播,即FF-FF…; 反向不成立,MAC广播时**,IP可指定

3. MAC&IP综合⭐

| image.png
如图网络结构,其中A-F为hosts,H,S,R分别代表hub,switch,router,则:
①为了确保A-F可以连入Internet,则R1上运行什么服务
②E如果要发送IP datagram pkt给F,则E怎样直接发给F而不会被传递给R2
③给定如下格式
image.jpeg
假设E->A发送IP datagram pkt,且网络中所有节点的ARP cache都是空的,按该格式给出E->A所有frame信息
④假设C->A发送IP datagram pkt,则C发出的frame与A接收的frame情况如何? | | —- |

  1. NAT服务(注意网络号明显不同,说明处于私有子网,尤其是注意192.168.1.0或者10.xx这类地址,且题中标出了以太网1,2,3,但注意1,3在虽然非同一子网内,但是划分自一个共有地址块无需NAT)
  2. S1查询交换表,frame中的dest MAC对应接口一定指向F,指向对F的转发
  3. 如下

image.png

  1. 如下(忽略ARP),C->A需要在R2进行NAT,因此R2处发出的pkt中src IP变成了R2#1 | | src MAC | dest MAC | src IP | dest IP | | —- | —- | —- | —- | —- | | C发 | C | R2#2 | C | A | | A收 | R2#1 | A | R2#1 | A |

**NAT才会使得路由器出口的frame中IP改变

4. Cache,DHCP.DNS,MAC综合⭐

| After getting the IP address 192.168.1.4, the local DNS server and the web proxy of the new host is set as 192.168.1.2 and 192.168.1.3, respectively. Now, the user of the new host wants to access an url on the web server www.scu.edu.cn. Luckily the DNS cache of local DNS server has cached the RR of www.scu.edu.cn. On the other hand, ARP table of all the nodes in fig 3 are empty. Please list the sequence of all the packets sent/received by the new host as well as any other packets sent/received by as other nodes. Please indicate the source and destination MAC address as well as the source and destination IP address of each packets | | —- | | image.png |

共22步

pkt src MAC dest MAC src IP dest IP
New host->Web cache(ARP广播) 66 FF 192.168.1.4 192.168.1.3
Web cache->New host(返回Mac) 55 66 192.168.1.3 192.168.1.4
TCP SYN 66 55 1.4 1.3
SYN ACK 55 66 1.3 1.4
New host-> cache(Http request) 66 55 1.4 1.3
cache->DNS server
(cache空,改作server解析DNS,ARP广播)		 55 FF 1.3 1.2
DNS server -> Cache (返回MAC) 44 55 1.2 1.3
Cache->DNS server(DNS请求) 55 44 1.3 1.2
DNS server ->Cache(DNS响应) 44 55 1.2 1.3
Cache->Router (ARP广播) 55 FF 1.3 1.1
Router->Cache (返回Mac) 33 55 1.1 1.3
Cache->Router (SYN)* 55 33 1.3 1.8**
Router-> Dest (ARP广播) 22 FF 1 18
destination -> Router(返回Mac) 11 22 18
(NAT,非1.3)		 1
Router-> Dest (SYN) 22 11 1 18
Dest->Router(SYN ACK) 11 22 18 1
Router->Cache(SYN ACK) 33 55 1.1 1.3
Cache->Router (HTTP request) 55 33 1.3 1.1
Router-> Dest (HTTP request) 22 11 1 18
Dest->Router(HTTP reponse) 11 22 18 1
Router->Cache(HTTP reponse) 33 55 1.1 1.3
Cache->New host(HTTP response) 55 66 1.3 1.4

实际流程如下:
image.png

**