-
《
Computer Networks and
Internet
》
Chapter
2
1.
Consider
the
following
string
of
ASCII
characters
that
were
captured
by
Wireshark when the browser sent an HTTP
GET message (i.e., this is the actual
content of an HTTP GET message). The
characters
and line-feed characters (that is, the
italized character string
represents the single carriage-return
character that was contained at that point in
the HTTP header). Answer the following
questions, indicating where in the HTTP
GET message below you find the
answer.
GET /cs453/
HTTP/1.1
Mozilla/5.0 (Windows;U; Windows NT 5.1;
en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax)
text/plain;q=0.8,image
/png,*/*;q=0.5
en-us,en;q=0.5
ISO-
8859-1,utf-8;q=0.7,*;q=0.7
300
a.
What is the URL of the document requested by the
browser?
b. What version of HTTP is the
browser running?
c. Does the browser
request a non-persistent or a persistent
connection?
d. What is the IP address
of the host on which the browser is running?
e. What type of browser initiates this
message? Why is the browser type needed in an
HTTP request message?
考虑以下的<
/p>
ASCII
字符字符串被
Wiresha
rk
当浏览器发送一个
HTTP GET
消息
(
即。
,
这是一个
HTTP GET
消息的实际
内容
)
。字符
< cr > < >
如果是回车和换行符字符
(
即
italized
下面的文本字符串
< cr
>
代表单一回车字符包含在
这一点上的
HTTP
头
)
。回答下列问题
,
表明在
HTTP
GET
消息下面你找到答案。
a
。什么是文档的
URL
请求的浏览器
?
b
。浏览器运行
HTTP
版本是什么
?
c
。浏览器请求一个非持久性或持久连接
?
d
。什么是浏览器的
IP
地址的主机运行吗<
/p>
?
e
。什么样的浏览器启动这个消息吗
?
为什么浏览器类型所需的
HTTP<
/p>
请求消息吗
?
1
浏览器类型信息需要由服务器发送同一对象的不同版本
,
不同类型的浏览器。
2. The text below shows the reply sent
from the server in response to the HTTP GET
message in the question above. Answer
the following questions, indicating where in
the message below you find the
answer.
HTTP/1.1 200
OK
Date: Tue, 07 Mar
2008
12:39:45GMT
Server:
Apache/2.0.52
(Fedora)
ETag:
526c3-f22-
a88a4c80”
Connection: Keep-
Alive
Accept-Ranges:
bytes
Content-Length:
3874
Keep-
Alive: timeout=max=100
Content-Type:
text/html; charset=ISO-8859-1
-//w3c//dtd html 4.0
transi
tional//en”>
equiv=”Content
-
Type”content=”text/html;
charset=iso-8859-
1”>
U) Netscape]”>
<<
/p>
much more document text following here
(not shown)
>
a.
Was
the
server
able
to
successfully
find
the
document
or
not?
What
time
was
the
document
reply provided?
b. When was the
document last modified?
c. How many
bytes are there in the document being returned?
d. What are the first 5 bytes of the
document being returned? Did the server agree to a
persistent connection?
下面的文本显示来自服务器的应答发送响应
HTTP
GET
消息在上面的问题中。回答下列问题
,<
/p>
显示下面的消息
,
你
找到答案。
一个。服务器能够成功地找到文档吗
?
文档回复提供时间是什么
?
b
。最后修改的文档是什么时候
?
c
。有多少字节的文档返回
?
d
。第一个是什么
5
字节的文档返回
?
服务器同意一个持久连接吗
< br>?
3. Consider following Figure, for which
there is an institutional network connected to
the
Internet.
Suppose
that
the
average
object
size
is
900kb
and
that the
average
re
quest
rate from the institution’s browsers to the origin
servers is 1
5 requests per
second. Also suppose that the amount of
time it takes from when the router on the
Internet
side
of
the
access
link
forwards
an
HTTP
request
until
it
receives
the
response is 3s on average. Model the
total average response time as the sum of the
average access delay (that is, the
delay from Internet router to institution router)
and the average
Internet
delay. For the average access delay, use
Δ/(1–Δ
β
), where
Δ
is the
average time required to send an
object over the access link and
β
is the
arrival rate of objects to the access
link.
2
Figure 1
Bottleneck between an
institutional network and the Internet
a. Find the total average response
time.
b. Now suppose a cache is
installed in the institutional LAN. Suppose the
miss rate is
0.4. Suppose hit rate
increases to 0.95. Find the total response time. <
/p>
考虑下面的图
,
有一个机构网络连接到互
联网。
假设对象的平均尺寸是
900 kb,
< br>平均请求率从机构的浏览器起源
服务器每秒
15
请求。
还假设的时间在互联网上需要从路由器的访问链接转发
HTTP
请求
,
直到接收
到响应平均
3
s
。模型总平均响应时
间平均访问延迟之和
(
即延迟从互联网路由器到路由器
)
机构和平均网络延迟。平均
访问延迟
,
使用
Δ/(1
-
Δβ),Δ
发送对象所需的平均时间的访问链接和
< br>β
的到达率是对象的访问链接。
发现总平均响应时间。
b
。现在假设一个缓存是安装在机构局域网。想错过率是
0.4
。假设命中率增加到
0.95
。发现总响应时间。<
/p>
4. Print out the
header of an e-mail message you have recently
received. How many
Received
:
header lines are there? Analyze each of the header
lines in the message.
(Allow printing
of an email header file.)
打印头你最近收到的一封电子
邮件。多少接受
:
头行吗
?
分析每个头线的消息。
(
允许打印头文件的电子邮
件。
)
3
5.
Read
RFC
5321
for
SMTP.
What
does
MTA
stand
for?
Consider
the
following
received
spam
email
(modified
from
a
real
spam
email).
Assuming
only
the
originator of this spam email is
malacious and all other hosts are honest, identify
the malacious host that has generated
this spam email.
为
SMTP
读
RFC 5321
。
MT
A
代表什么
?
考虑以下收到垃圾邮件从
一个真正的垃圾邮件
(
修改
)
。假设只
malacious
这个垃圾邮件的发
起者和所有其他主机是诚实的
,
识别
m
alacious
主机生成的这个垃圾邮件。
From - Fri Nov 07 13:41:30 2008
Return-Path:
Received: from
(
[128.119.240.3]) by (8.13.1/8.12.6) for
Nov 2008 13:27:10 -0500
Received:
from
asusus-4b96
(localhost
[127.0.0.1])
by
(Spam
Firewall)
for
Received: from
asusus-4b96 ([58.88.21.177]) by for
Nov 2008 13:27:07 -0500 (EST)
Received: from [58.88.21.177] by Sat,
8 Nov 2008 01:27:07 +0700
From:
To:
Subject: How to
secure your savings
MTA
stands for Mail Transfer Agents. A mail is
forwarded by a source to a MTA and then it follows
a
sequence of MTAs to reach the
receiver’s mail reader.
We
see that this spam email follows a chain of
MTAs.
An
honest
MTA
should
report
where
it
receives
the
message.
Notice
that
in
this
email,
“asusus
-
4b96
([58.88.21.177])” does not report where it
receives the email. As we assume that the only
the originator is dishonest, so
“asusus
-
4b96
([58.88.21.177])” must be the
originator.
MTA
代表
邮件传输代理。邮件转发由源到
MTA
然后遵循一系列放在到达
接收方的邮件阅读器。我们看到这个垃
圾邮件之前放在链。一个诚实的
< br>MTA
应该报告接收消息。注意
,
在这封邮件中
,“asusus
-
4
b96([58.88.21.177])“
不
报告接收电子邮
件。当我们假定唯一的发起人是不诚实的
,
所以
“asusus
-
4b96([58.88.21.1
77])”
必须发起人。
6.
Answer
the
following
question,
using
the
WHOIS
Tools
(such
as,
SmartWhois,
WhereIsIP
,CountryWhois, /) and nslookup.
a. What
is a whois database?
b. Use various
whois databases on the Internet to obtain the
names of two DNS servers.
Indicate
which whois databases you used. (such as, , ,
, )
c.
Use
nslookup
on
your
local
host
to
send
DNS
queries
to
three
DNS
servers:
your
local DNS server and the two DNS
servers
you found in part (b). Try
querying for
Type A, NS, and MX
reports. Summarize your findings.
d.
Use
nslookup
to
find
a
Web
server
that
has
multiple
IP
addresses.
Does
the
Web
server of
BUPT have multiple IP addresses?
e.
Use
the
ARIN
whois
database
to
determine
the
IP
address
range
used
by
your
institution (such as,. , , ).
回答下列问题
,
使用
WHOIS<
/p>
工具
(
如
Sma
rtWhois
WhereIsIP
,CountryWho
is,/)
和网路资讯
查询。
4