CentOS6下DHCP服務（二）簡單配置案例及故障排查

1、預分配網絡參數如下：
linux服務器：eth0 IP為192.168.8.250  做為局域網DHCP服務器
局域網網段設置為192.168.8.0/24；
內部計算機的router為192.168.8.254；
DNS主機為聯通的202.102.224.68和202.102.227.68
每個用戶默認租約為3天(3*24*60*60=259200秒），最長為6天
要分配的IP范圍只有192.168.8.101至192.168.8.199，其他IP則保留

2、根據網絡參數，編輯DHCP服務配置文件/etc/dhcp/dhcpd.conf如下：

#整體環境設置

ddns-update-style  none;
ignore client-update ;
default-lease-time  259200;
max-lease-time     518400;
option routers  192.168.8.254;
option domain-name    "centos.me"
option  domain-name-servers  202.102.224.68,202.102.227.68;

#IP分配

subnet  192.168.8.0 netmask 255.255.255.0 {
    range  192.168.8.101   192.168.8.199;
    }

3、dhcp服務器的啟動與觀察

3.1 啟動前要注意
    1、linux服務器的網絡環境已經設置好
    2、防火牆規則已經處理好



如果以上都設置好了那么現在開始啟動dhcp
[root@NMS dhcp]# /etc/init.d/dhcpd start
正在啟動 dhcpd：                                           [失敗]

很不幸!失敗了~那么為什么會失敗呢？我們來查看下啟動日志/var/log/messages
這里面記錄了dhcp的啟動過程，都發生了什么！

[root@NMS dhcp]# tail  -n 30 /var/log/messages
Aug 31 12:25:00 NMS rsyslogd: [origin software="rsyslogd" swVersion="5.8.10" x-pid="1214" x-info="http://www.rsyslog.com"] rsyslogd was HUPed
Aug 31 15:40:48 NMS dhcpd: Internet Systems Consortium DHCP Server 4.1.1-P1
Aug 31 15:40:48 NMS dhcpd: Copyright 2004-2010 Internet Systems Consortium.
Aug 31 15:40:48 NMS dhcpd: All rights reserved.
Aug 31 15:40:48 NMS dhcpd: For info, please visit https://www.isc.org/software/dhcp/
Aug 31 15:40:48 NMS dhcpd: /etc/dhcp/dhcpd.conf line 4: expecting allow/deny key
Aug 31 15:40:48 NMS dhcpd: ignore client-update
Aug 31 15:40:48 NMS dhcpd:         ^
Aug 31 15:40:48 NMS dhcpd: /etc/dhcp/dhcpd.conf line 4: expecting a parameter or declaration
Aug 31 15:40:48 NMS dhcpd: ignore client-update ;
Aug 31 15:40:48 NMS dhcpd:                       ^
Aug 31 15:40:48 NMS dhcpd: /etc/dhcp/dhcpd.conf line 9: semicolon expected.
Aug 31 15:40:48 NMS dhcpd: option
Aug 31 15:40:48 NMS dhcpd:  ^
Aug 31 15:40:48 NMS dhcpd: Configuration file errors encountered -- exiting
Aug 31 15:40:48 NMS dhcpd:
Aug 31 15:40:48 NMS dhcpd: This version of ISC DHCP is based on the release available
Aug 31 15:40:48 NMS dhcpd: on ftp.isc.org.  Features have been added and other changes
Aug 31 15:40:48 NMS dhcpd: have been made to the base software release in order to make
Aug 31 15:40:48 NMS dhcpd: it work better with this distribution.
Aug 31 15:40:48 NMS dhcpd:
Aug 31 15:40:48 NMS dhcpd: Please report for this software via the CentOS Bugs Database:
Aug 31 15:40:48 NMS dhcpd:     http://bugs.centos.org/
Aug 31 15:40:48 NMS dhcpd:
Aug 31 15:40:48 NMS dhcpd: exiting.

由日志我們看出來配置文件錯誤造成dhcp啟動失敗，“Configuration file errors encountered -- exiting”
那么我來看配置文件，根據提示找出其中的錯誤；

[root@NMS dhcp]# cat  -n  /etc/dhcp/dhcpd.conf
     1    #整體環境設置
     2    
     3    ddns-update-style  none;
     4    ignore client-update ;
     5    default-lease-time  259200;
     6    max-lease-time     518400;
     7    option routers  192.168.8.254;
     8    option domain-name    "centos.me"
     9    option  domain-name-servers  202.102.224.68,202.102.227.68;
    10    
    11    #IP分配
    12    
    13    subnet  192.168.8.0 netmask 255.255.255.0 {
    14        range  192.168.8.101   192.168.8.199;
    15        }
    16        
第一個錯誤信息表示配置文件第4行有錯誤，是關鍵字錯誤！仔細看是update少了個s應該是updates
Aug 31 15:40:48 NMS dhcpd: /etc/dhcp/dhcpd.conf line 4: expecting allow/deny key
Aug 31 15:40:48 NMS dhcpd: ignore client-update
第二個錯誤也是在第4行，根據指數符號（^）標注的位置，原來配置項結束后要緊接";"，我不小多了個空格，所以報錯
Aug 31 15:40:48 NMS dhcpd: /etc/dhcp/dhcpd.conf line 4: expecting a parameter or declaration
Aug 31 15:40:48 NMS dhcpd: ignore client-update ;
第三個錯誤指出錯誤在第9行，可以看出我們在最后沒有加";"所以報錯，semicolon是分號的意思；
Aug 31 15:40:48 NMS dhcpd: /etc/dhcp/dhcpd.conf line 9: semicolon expected.
Aug 31 15:40:48 NMS dhcpd: option

按照日志信息更改后的配置文件如下：
[root@NMS etc]# cat /etc/dhcp/dhcpd.conf  -n
     1    #整體環境設置
     2    
     3    ddns-update-style  none;
     4    ignore client-updates;
     5    default-lease-time  259200;
     6    max-lease-time     518400;
     7    option routers  192.168.8.254;
     8    option domain-name    "centos.me";
     9    option  domain-name-servers  202.102.224.68,202.102.227.68;
    10    
    11    #IP分配
    12    
    13    subnet  192.168.8.0 netmask 255.255.255.0 {
    14        range  192.168.8.101   192.168.8.199;
    15        }
    16        
 
接下來再次啟動DHCP，

[root@NMS etc]# /etc/init.d/dhcpd start
正在啟動 dhcpd：                                           [確定]

可以看到這次能啟動了。

DHCP使用的端口是port 67,查看端口是否監聽；
[root@NMS etc]# netstat -tlunp |grep dhcp
udp        0      0 0.0.0.0:67                  0.0.0.0:*                               17017/dhcpd         

再次查看日志文件輸出信息

[root@NMS etc]# tail -n  10 /var/log/messages
Aug 31 16:09:16 NMS dhcpd: Internet Systems Consortium DHCP Server 4.1.1-P1
Aug 31 16:09:16 NMS dhcpd: Copyright 2004-2010 Internet Systems Consortium.
Aug 31 16:09:16 NMS dhcpd: All rights reserved.
Aug 31 16:09:16 NMS dhcpd: For info, please visit https://www.isc.org/software/dhcp/
Aug 31 16:09:16 NMS dhcpd: Not searching LDAP since ldap-server, ldap-port and ldap-base-dn were not specified in the config file
Aug 31 16:09:16 NMS dhcpd: Wrote 0 leases to leases file.
Aug 31 16:09:16 NMS dhcpd: Listening on LPF/eth0/00:0c:29:23:fe:20/192.168.8.0/24
Aug 31 16:09:16 NMS dhcpd: Sending on   LPF/eth0/00:0c:29:23:fe:20/192.168.8.0/24
Aug 31 16:09:16 NMS dhcpd: Sending on   Socket/fallback/fallback-net

看到這些信息說明成功了！沒有報錯！

4、服務器端已經准備好，萬事俱備只欠東風了就等給客戶端服務了！接下來看下客戶端的設置
4.1客戶端是linux

客戶端環境
[root@nmserver-7 ~]# uname -a
Linux nmserver-7.test.com 3.10.0-514.el7.centos.plus.i686 #1 SMP Wed Jan 25 12:55:04 UTC 2017 i686 i686 i386 GNU/Linux
[root@nmserver-7 ~]# cat /etc/redhat-release
CentOS release 7.3.1611 (AltArch)

在客戶端修改網卡配置文件，讓主機自動取得網絡參數；
[root@nmserver-7 ~]# vi /etc/sysconfig/network-scripts/ifcfg-ens33

TYPE=Ethernet
DEVICE=ens33
ONBOOT=yes
BOOTPROTO=dhcp

~                                                                                                                                                
                                                                                                                                            
~                                                                                                                                                
"/etc/sysconfig/network-scripts/ifcfg-ens33" 5L, 54C

注意：重點是將BOOTPROTO由原來的靜態“static“，改為”dhcp“就可通過dhcp服務器來獲取網絡參數了！


修改配置文件后重啟客戶端網絡
[root@nmserver-7 ~]# systemctl restart network

查看IP，可以看到客戶端已經獲取到的IP是192.168.8.101/24
[root@nmserver-7 ~]# ifconfig
bridge0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether b6:83:d4:66:3a:4c  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

ens33: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.8.101  netmask 255.255.255.0  broadcast 192.168.8.255
        inet6 fe80::20c:29ff:fe56:bccf  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:56:bc:cf  txqueuelen 1000  (Ethernet)
        RX packets 29323  bytes 2119863 (2.0 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 29052  bytes 2256533 (2.1 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1  (Local Loopback)
        RX packets 2212  bytes 150063 (146.5 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 2212  bytes 150063 (146.5 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

查看一下客戶端路由
[root@nmserver-7 ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.8.254   0.0.0.0         UG    100    0        0 ens33
192.168.8.0     0.0.0.0         255.255.255.0   U     100    0        0 ens33

查看客戶端DHCP連接狀態，
[root@nmserver-7 ~]# netstat -tunlp |grep dhc
udp        0      0 0.0.0.0:68              0.0.0.0:*                           4195/dhclient       
udp        0      0 0.0.0.0:22424           0.0.0.0:*                           4195/dhclient       
udp6       0      0 :::56121                :::*                                4195/dhclient       
查看客戶端DNS設置
[root@nmserver-7 dhclient]# cat /etc/resolv.conf
# Generated by NetworkManager
search centos.me test.com
nameserver 202.102.224.68
nameserver 202.102.227.68
 

通過以上信息可以看到客戶端獲取的網絡參數與之前DHCP服務器上設置的一致！！


那么在客戶端網絡重啟的過程中，DHCP服務器都做了什么呢？我們來看下DHCP服務器的日志信息，可以清楚看到
DHCP協議工作的4個過程：

[root@NMS etc]# tail -n  10 /var/log/messages
Aug 31 16:09:16 NMS dhcpd: Listening on LPF/eth0/00:0c:29:23:fe:20/192.168.8.0/24
Aug 31 16:09:16 NMS dhcpd: Sending on   LPF/eth0/00:0c:29:23:fe:20/192.168.8.0/24
Aug 31 16:09:16 NMS dhcpd: Sending on   Socket/fallback/fallback-net
Aug 31 16:52:21 NMS dhcpd: DHCPDISCOVER from 00:0c:29:56:bc:cf via eth0                             #IP租用請求
Aug 31 16:52:22 NMS dhcpd: DHCPOFFER on 192.168.8.101 to 00:0c:29:56:bc:cf (nmserver-7) via eth0　　#IP租用提供
Aug 31 16:52:22 NMS dhcpd: DHCPREQUEST for 192.168.8.101 (192.168.8.6) from 00:0c:29:56:bc:cf (nmserver-7) via eth0 #IP租用選擇
Aug 31 16:52:22 NMS dhcpd: DHCPACK on 192.168.8.101 to 00:0c:29:56:bc:cf (nmserver-7) via eth0  #IP租用確認

查看DHCP服務器與客戶端的租約信息，

[root@NMS etc]# cat /var/lib/dhcpd/dhcpd.leases
# The format of this file is documented in the dhcpd.leases(5) manual page.
# This lease file was written by isc-dhcp-4.1.1-P1

lease 192.168.8.101 {
  starts 4 2017/08/31 09:22:42;
  ends 0 2017/09/03 09:22:42;
  cltt 4 2017/08/31 09:22:42;
  binding state active;
  next binding state free;
  hardware ethernet 00:0c:29:56:bc:cf;
  client-hostname "nmserver-7";
}
server-duid "\000\001\000\001!:\200\254\000\014)#\376 ";

從這個文件里面我們就知道有多少個客戶端已經向DHCP申請IP了。目前只有一個客戶端：
客戶端主機名：nmserver-7
MAC地址：00:0c:29:56:bc:cf
客戶端IP：192.168.8.101