1. 問(wèn)題背景

不同品牌的交換機(jī)通過(guò)dhcp請(qǐng)求，獲取到不同的bootfile-name。

2. 抓包分析

2.1. 抓包命令

tcpdump -n -s0 -i eth0 net 198.19 -w ./dhcp.pcap

2.2. 包分析

使用wireshark來(lái)分析數(shù)據(jù)包的內(nèi)容。這里只展示了部分信息。
只分析 DHCP Discover 就可以。

1. 銳捷交換機(jī)

使用： Option: (12) Host Name

...
    Option: (53) DHCP Message Type (Discover)
    Option: (61) Client identifier
    Option: (12) Host Name
        Length: 6
        Host Name: Ruijie
    Option: (55) Parameter Request List
    Option: (255) End
    Padding: 000000000000000000000000000000000000000000000000…

2. 華為交換機(jī)

使用： Option: (60) Vendor class identifier

...
    Option: (53) DHCP Message Type (Discover)
    Option: (55) Parameter Request List
    Option: (60) Vendor class identifier
        Length: 15
        Vendor class identifier: HUAWEI CE5855EI
    Option: (61) Client identifier
    Option: (255) End

3. 華三交換機(jī)

使用： Option: (60) Vendor class identifier

...
    Option: (53) DHCP Message Type (Discover)
    Option: (55) Parameter Request List
    Option: (57) Maximum DHCP Message Size
    Option: (60) Vendor class identifier
        Length: 19
        Vendor class identifier: H3C. H3C S6850-56HF
    Option: (61) Client identifier
    Option: (255) End
    Padding: 0000000000000000

3. dhcp配置

group host_pool {
    allow bootp;
    allow booting;


    default-lease-time 1800;
    max-lease-time 2400;

    #是的，不是0,5.確實(shí)是0,6。代表前6個(gè)字符
    if substring (option host-name, 0, 6) = "Ruijie" {
        option tftp-server-name "192.168.1.254";
        option bootfile-name "ruijie.py";
    }
    else if substring (option vendor-class-identifier, 0, 6) = "HUAWEI" {
        option tftp-server-name "192.168.1.254";
        option bootfile-name "huawei.py";
    }
    else if substring (option vendor-class-identifier, 0, 3) = "H3C" {
        option tftp-server-name "192.168.1.254";
        option bootfile-name "h3c.py";
    }
    else {
        next-server 192.168.1.254;
        filename "default.py";
    }
    #也可以匹配mac地址分析，不同品牌的交換機(jī)，前三位的mac不一樣。不過(guò)此方法不太好
    #if substring (hardware, 1, 3) = 00:74:9c {
    #    option tftp-server-name "192.168.1.254";
    #    option bootfile-name "ruijie.py";
    #}


    subnet 198.168.0.0  netmask 255.255.255.0 {option routers 198.168.0.254   ; range 198.168.0.151 198.168.0.169;}

}