Linux日志中出现大量dhclient mesage浅析

最近检查发现一台linux服务器，发现其日志里面有大量下面信息，其中部分信息做了脱敏处理。其中一个地址a(192.168.aaa.aaa) 为dns服务器地址,地址b(192.168.bbb.bbb)为动态获取的ip地址。

 

 

#脱敏后信息如下所示：

 

jul 24 15:14:18 xxxxxx dhclient: dhcprequest on eth0 to 192.168.aaa.aaa port 67 (xid=0x1ff3cda3)

jul 24 15:14:18 xxxxxx dhclient: dhcpack from 192.168.aaa.aaa (xid=0x1ff3cda3)

jul 24 15:14:18 xxxxxx dhclient: bound to 192.168.bbb.bbb -- renewal in 863 seconds.

jul 24 15:28:41 xxxxxx dhclient: dhcprequest on eth0 to 192.168.aaa.aaa port 67 (xid=0x1ff3cda3)

jul 24 15:28:41 xxxxxx dhclient: dhcpack from 192.168.aaa.aaa (xid=0x1ff3cda3)

jul 24 15:28:41 xxxxxx dhclient: bound to 192.168.bbb.bbb -- renewal in 681 seconds.

jul 24 15:40:02 xxxxxx dhclient: dhcprequest on eth0 to 192.168.aaa.aaa port 67 (xid=0x1ff3cda3)

jul 24 15:40:02 xxxxxx dhclient: dhcpack from 192.168.aaa.aaa (xid=0x1ff3cda3)

jul 24 15:40:02 xxxxxx dhclient: bound to 192.168.bbb.bbb -- renewal in 763 seconds.

 

那么dhcprequest、dhcpack是什么东西呢？ 初步判断很有可能是服务器动态申请ip（dhcp）的相关性。然后搜索了相关资料验证一下：

 

dhcprequest简介：

 

dhcp请求（request） 当客户pc收到一个ip租约提供时，它必须告诉所有其他的dhcp服务器它已经接受了一个租约提供。因此，该客户会发送一个dhcprequest消息，其中包含提供租约的服务器的ip。当其他dhcp服务器收到了该消息后，它们会收回所有可能已提供给该客户的租约。然后它们把曾经给该客户保留的那个地址重新放回到可用地址池中，这样，它们就可以为其他计算机分配这个地址。任意数量的dhcp服务器都可以响应同一个ip租约请求，但是每一个客户网卡只能接受一个租约提供。

 

dhcpack简介：

当dhcp服务器收到来自客户的request消息后，它就开始了配置过程的最后阶段。这个响应阶段包括发送一个dhcpack包给客户。这个包包含租期和客户可能请求的其他所有配置信息。这时候，tcp/ip配置过程就完成了。

 

但是这台服务器不是设置的静态ip吗？ 怎么会有dhcp的相关日志呢？ 首先检查确认地址a(192.168.aaa.aaa)为一个dns服务器地址。如下所示：

 

[root@xxxx log]# more /etc/resolv.conf

; generated by /sbin/dhclient-script

search eel1.esquel.com

nameserver 192.168.aaa.aaa

nameserver 192.168.xxx.xxx

 

然后查看该服务器的ip地址。如下所示：

 

[root@xxxxx log]# ifconfig
eth0      link encap:ethernet  hwaddr 00:0c:29:af:0f:87 
          inet addr:192.168.bbb.bbb  bcast:192.168.xxx.xxx  mask:255.255.255.0
          up broadcast running multicast  mtu:1500  metric:1
          rx packets:1113647339 errors:0 dropped:0 overruns:0 frame:0
          tx packets:5394185429 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          rx bytes:232836326224 (216.8 gib)  tx bytes:7577117537336 (6.8 tib)

lo        link encap:local loopback 
          inet addr:127.0.0.1  mask:255.0.0.0
          up loopback running  mtu:16436  metric:1
          rx packets:943142413 errors:0 dropped:0 overruns:0 frame:0
          tx packets:943142413 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          rx bytes:37841765933 (35.2 gib)  tx bytes:37841765933 (35.2 gib)

 

检查发现这个网络绑定了两个ip地址。如下所示所示（其中192.168.ccc.ccc为静态ip地址）,最让人惊奇的是ifconfig中显示的是动态ip地址，而不是ifcfg-eth0设置的静态ip地址

 

[root@xxxxx log]# ip addr show eth0

2: eth0: <broadcast,multicast,up,lower_up> mtu 1500 qdisc pfifo_fast qlen 1000

    link/ether 00:0c:29:af:0f:87 brd ff:ff:ff:ff:ff:ff

    inet 192.168.bbb.bbb/24 brd 192.168.152.255 scope global eth0

    inet 192.168.ccc.cc/24 brd 192.168.152.255 scope global secondary eth0

[root@xxx network-scripts]# more ifcfg-eth0 

# intel corporation 82545em gigabit ethernet controller (copper)

device=eth0

bootproto=none

onboot=yes

hwaddr=00:0c:29:af:0f:87

netmask=255.255.255.0

ipaddr=192.168.ccc.ccc

gateway=192.168.xxx.xxx

type=ethernet

userctl=no

ipv6init=no

peerdns=yes

 

个人猜测是因为local的系统管理员，不知出于什么原因给网卡多绑定了一个地址，下面在测试服务器，做了一个简单的测试。如果网络设置动态获取ip地址，基本上就会有这类信息出现，

 

jul 20 13:01:49 db-server dhclient: bound to 10.20.57.24 -- renewal in 12333 seconds.

jul 20 16:27:22 db-server dhclient: dhcprequest on eth0 to 192.168.27.210 port 67 (xid=0x293091fd)

jul 20 16:27:22 db-server dhclient: dhcpack from 192.168.27.210 (xid=0x293091fd)

jul 20 16:27:22 db-server dhclient: bound to 10.20.57.24 -- renewal in 11811 seconds.

jul 20 19:44:12 db-server dhclient: dhcprequest on eth0 to 192.168.27.210 port 67 (xid=0x293091fd)

jul 20 19:44:13 db-server dhclient: dhcpack from 192.168.27.210 (xid=0x293091fd)

jul 20 19:44:13 db-server dhclient: bound to 10.20.57.24 -- renewal in 13245 seconds.

jul 20 23:24:58 db-server dhclient: dhcprequest on eth0 to 192.168.27.210 port 67 (xid=0x293091fd)

jul 20 23:24:58 db-server dhclient: dhcpack from 192.168.27.210 (xid=0x293091fd)

jul 20 23:24:58 db-server dhclient: bound to 10.20.57.24 -- renewal in 13115 seconds.

jul 21 03:03:32 db-server dhclient: dhcprequest on eth0 to 192.168.27.210 port 67 (xid=0x293091fd)

jul 21 03:03:33 db-server dhclient: dhcpack from 192.168.27.210 (xid=0x293091fd)

jul 21 03:03:33 db-server dhclient: bound to 10.20.57.24 -- renewal in 13533 seconds.

 

测试过程中也发现，如果第一个地址是静态ip地址，第二个（secondary）地址为动态地址，在message里面也没有出现上面的dhcprequest 、dhcpack日志信息。但是如果网卡的第一个地址为动态地址就会在message中出现dhcp相关日志。

 

[root@db-server network-scripts]# ifconfig eth0

eth0      link encap:ethernet  hwaddr b0:83:fe:55:32:e5  

          inet addr:10.20.57.24  bcast:10.255.255.255  mask:255.0.0.0

          up broadcast running multicast  mtu:1500  metric:1

          rx packets:230 errors:0 dropped:0 overruns:0 frame:0

          tx packets:162 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:1000 

          rx bytes:22435 (21.9 kib)  tx bytes:20666 (20.1 kib)

          interrupt:233 base address:0x4000 

[root@db-server network-scripts]# more /etc/resolv.conf

; generated by /sbin/dhclient-script

search gfg1.esquel.com

nameserver 192.168.xxx.xxx

nameserver 192.168.xxx.xxx

[root@db-server network-sc

[root@db-server network-scripts]# ifconfig eth0:1 10.20.57.26 netmask 255.0.0.0

[root@db-server network-scripts]# ip addr show eth0

2: eth0: <broadcast,multicast,up,lower_up> mtu 1500 qdisc pfifo_fast qlen 1000

    link/ether b0:83:fe:55:32:e5 brd ff:ff:ff:ff:ff:ff

    inet 10.20.57.24/8 brd 10.255.255.255 scope global eth0

    inet 10.20.57.26/8 brd 10.255.255.255 scope global secondary eth0:1

 

 

 

参考资料：

 

https://zh.wikipedia.org/zh-hans/%e5%8a%a8%e6%80%81%e4%b8%bb%e6%9c%ba%e8%ae%be%e7%bd%ae%e5%8d%8f%e8%ae%ae