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一个客户端用DHCP CLIENT 从DHCP SERVER那里拿IP,标准流程如下(用ubuntu 下dhcpdump抓包):
1)DHCP-DISCOVER
TIME: 2011-04-07 09:43:43.422
IP: 0.0.0.0 (c8:a:a9:9e:14:a5) > 255.255.255.255 (ff:ff:ff:ff:ff:ff)
OP: 1 (BOOTPREQUEST)
HTYPE: 1 (Ethernet)
HLEN: 6
HOPS: 0
XID: 3a8471d5
SECS: 0
FLAGS: 0
CIADDR: 0.0.0.0
YIADDR: 0.0.0.0
SIADDR: 0.0.0.0
GIADDR: 0.0.0.0
CHADDR: c8:0a:a9:9e:14:a5:00:00:00:00:00:00:00:00:00:00
SNAME: .
FNAME: .
OPTION: 53 ( 1) DHCP message type 1 (DHCPDISCOVER)
OPTION: 61 ( 7) Client-identifier 01:c8:0a:a9:9e:14:a5
OPTION: 60 ( 12) Vendor class identifier udhcp 1.13.3
OPTION: 57 ( 2) Maximum DHCP message size 576
OPTION: 55 ( 7) Parameter Request List 1 (Subnet mask)
3 (Routers)
6 (DNS server)
12 (Host name)
15 (Domainname)
28 (Broadcast address)
42 (NTP servers)
---------------------------------------------------------------------------
2)DHCP-OFFER
TIME: 2011-04-07 09:43:43.422
IP: 10.10.50.10 (0:13:72:4e:2a: > 10.10.50.243 (c8:a:a9:9e:14:a5)
OP: 2 (BOOTPREPLY)
HTYPE: 1 (Ethernet)
HLEN: 6
HOPS: 0
XID: 3a8471d5
SECS: 0
FLAGS: 0
CIADDR: 0.0.0.0
YIADDR: 10.10.50.243
SIADDR: 10.10.50.10
GIADDR: 0.0.0.0
CHADDR: c8:0a:a9:9e:14:a5:00:00:00:00:00:00:00:00:00:00
SNAME: .
FNAME: .
OPTION: 53 ( 1) DHCP message type 2 (DHCPOFFER)
OPTION: 54 ( 4) Server identifier 10.10.50.10
OPTION: 51 ( 4) IP address leasetime 86400 (24h)
OPTION: 1 ( 4) Subnet mask 255.255.255.0
OPTION: 3 ( 4) Routers 10.10.50.1
OPTION: 6 ( DNS server 10.10.50.10,10.10.50.11
---------------------------------------------------------------------------
3)DHCP-REQUEST
TIME: 2011-04-07 09:43:43.445
IP: 0.0.0.0 (c8:a:a9:9e:14:a5) > 255.255.255.255 (ff:ff:ff:ff:ff:ff)
OP: 1 (BOOTPREQUEST)
HTYPE: 1 (Ethernet)
HLEN: 6
HOPS: 0
XID: 3a8471d5
SECS: 0
FLAGS: 0
CIADDR: 0.0.0.0
YIADDR: 0.0.0.0
SIADDR: 0.0.0.0
GIADDR: 0.0.0.0
CHADDR: c8:0a:a9:9e:14:a5:00:00:00:00:00:00:00:00:00:00
SNAME: .
FNAME: .
OPTION: 53 ( 1) DHCP message type 3 (DHCPREQUEST)
OPTION: 61 ( 7) Client-identifier 01:c8:0a:a9:9e:14:a5
OPTION: 60 ( 12) Vendor class identifier udhcp 1.13.3
OPTION: 50 ( 4) Request IP address 10.10.50.243
OPTION: 54 ( 4) Server identifier 10.10.50.10
OPTION: 55 ( 7) Parameter Request List 1 (Subnet mask)
3 (Routers)
6 (DNS server)
12 (Host name)
15 (Domainname)
28 (Broadcast address)
42 (NTP servers)
---------------------------------------------------------------------------
4)DHCP-ACK
TIME: 2011-04-07 09:43:43.446
IP: 10.10.50.10 (0:13:72:4e:2a: > 10.10.50.243 (c8:a:a9:9e:14:a5)
OP: 2 (BOOTPREPLY)
HTYPE: 1 (Ethernet)
HLEN: 6
HOPS: 0
XID: 3a8471d5
SECS: 0
FLAGS: 0
CIADDR: 0.0.0.0
YIADDR: 10.10.50.243
SIADDR: 10.10.50.10
GIADDR: 0.0.0.0
CHADDR: c8:0a:a9:9e:14:a5:00:00:00:00:00:00:00:00:00:00
SNAME: .
FNAME: .
OPTION: 53 ( 1) DHCP message type 5 (DHCPACK)
OPTION: 54 ( 4) Server identifier 10.10.50.10
OPTION: 51 ( 4) IP address leasetime 86400 (24h)
OPTION: 1 ( 4) Subnet mask 255.255.255.0
OPTION: 3 ( 4) Routers 10.10.50.1
OPTION: 6 ( DNS server 10.10.50.10,10.10.50.11
---------------------------------------------------------------------------
我的疑问:
第2)步,DHCP CLIENT尚未分配IP,为何DHCP-OFFER报文的目的地址却已经是10.10.50.243?
这样DHCP CLIENT会怎么处理这个DHCP-OFFER报文?
很疑惑,求解答。 |
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