记一次Multicast DNS(mdns)的问题-(linux 下ifconfig)，mdnsifconfig
记一次Multicast DNS(mdns)的问题-(linux 下ifconfig)，mdnsifconfig
前言：近期在查询mdns的问题过程一波三折，问题总结下来可以分为三块，都是比较基础性的问题：
1.网关ifconfig查询地址
2.多个程序同时占用一个端口号占用编码问题
3.mdns协议及实现源码
mdns是用于局域网发现的一种协议，网关搭载的linux系统，首先得确定其使用的是哪个地址作为通讯，说一个最简单的指令：ifconfig，虽然早就知道这个指令，但是其实这个指令包含比较多的基础知识。
用我使用的openwrt路由器输入ifconfig:
br-lan Link encap:Ethernet HWaddr 04:A1:51:9A:03:67
inet addr:198.100.100.1 Bcast:198.100.100.255 Mask:255.255.255.0
inet6 addr: fdbb:e076:9029::1/60 Scope:Global
inet6 addr: fe80::6a1:51ff:fe9a:367/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:37358673 errors:0 dropped:0 overruns:0 frame:0
TX packets:49805372 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:10001210378 (9.3 GiB) TX bytes:49536338006 (46.1 GiB)
eth0 Link encap:Ethernet HWaddr BE:7F:7D:5D:09:D9
inet6 addr: fe80::bc7f:7dff:fe5d:9d9/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:71274265 errors:0 dropped:0 overruns:383 frame:0
TX packets:67972711 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:23375869 (22.2 MiB) TX bytes:4047624223 (3.7 GiB)
Interrupt:4
eth0.1 Link encap:Ethernet HWaddr BE:7F:7D:5D:09:D9
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:27485423 errors:0 dropped:0 overruns:0 frame:0
TX packets:32246955 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:8388027931 (7.8 GiB) TX bytes:32142311436 (29.9 GiB)
eth0.2 Link encap:Ethernet HWaddr 04:A1:51:9A:03:68
inet addr:193.168.1.125 Bcast:193.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::6a1:51ff:fe9a:368/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:43788842 errors:0 dropped:0 overruns:0 frame:0
TX packets:35727507 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:46186987470 (43.0 GiB) TX bytes:10288278423 (9.5 GiB)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:10489 errors:0 dropped:0 overruns:0 frame:0
TX packets:10489 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1066479 (1.0 MiB) TX bytes:1066479 (1.0 MiB)
wlan0 Link encap:Ethernet HWaddr 04:A1:51:9A:03:67
inet6 addr: fe80::6a1:51ff:fe9a:367/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:4839004 errors:0 dropped:0 overruns:0 frame:0
TX packets:5852922 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:670518236 (639.4 MiB) TX bytes:1589348208 (1.4 GiB)
wlan1 Link encap:Ethernet HWaddr 04:A1:51:9A:03:69
inet6 addr: fe80::6a1:51ff:fe9a:369/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:5443036 errors:0 dropped:0 overruns:0 frame:0
TX packets:9474688 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1115674576 (1.0 GiB) TX bytes:1268032438 (1.1 GiB)
此处br-lan,eth0,eth0.1…代表的是什么意思呢？
通过查阅，知道了其实在系统文件（network ,wireless）中针对有线和无线早有配置。
root@OpenWrt:/etc/config# cat network
config interface 'loopback'
option ifname 'lo'
option proto 'static'
option ipaddr '127.0.0.1'
option netmask '255.0.0.0'
config globals 'globals'
option ula_prefix 'fdbb:e076:9029::/48'
config interface 'lan'
option ifname 'eth0.1'
option force_link '1'
option type 'bridge'
option proto 'static'
option netmask '255.255.255.0'
option ip6assign '60'
option macaddr '04:a1:51:9a:03:67'
option ipaddr '198.100.100.1'
config interface 'wan'
option ifname 'eth0.2'
option proto 'dhcp'
option macaddr '04:a1:51:9a:03:68'
config interface 'wan6'
option ifname 'eth0.2'
option proto 'dhcpv6'
config switch
option name 'switch0'
option reset '1'
option enable_vlan '1'
config switch_vlan
option device 'switch0'
option vlan '1'
option ports '0t 1 2 3 4'
config switch_vlan
option device 'switch0'
option vlan '2'
option ports '0t 5'
root@OpenWrt:/etc/config# cat wireless
config wifi-device 'radio0'
option type 'mac80211'
option hwmode '11g'
option path 'platform/ar934x_wmac'
option htmode 'HT20'
option txpower '22'
option country 'US'
option channel '6'
config wifi-device 'radio1'
option type 'mac80211'
option channel '36'
option hwmode '11a'
option path 'pci0000:00/0000:00:00.0'
option htmode 'HT20'
option txpower '14'
option country 'US'
config wifi-iface
option device 'radio1'
option network 'lan'
option mode 'ap'
option ssid 'jthlw-cj5G'
option encryption 'psk-mixed'
option key '11223344'
config wifi-iface
option device 'radio0'
option mode 'ap'
option network 'lan'
option ssid 'jthlw-cj'
option encryption 'psk-mixed'
option key 'cjcjcj12345'
首先粘贴一张盗版的openwrt的架构：
网关的两个网卡：eth0,eht2分别为一个有线一个无线网卡，这是两个真实的网卡，是有对应的mac地址的。
通过配置
config interface 'lan'
option ifname 'eth0.1'
option force_link '1'
option type 'bridge'
option proto 'static'
option netmask '255.255.255.0'
option ip6assign '60'
option macaddr '04:a1:51:9a:03:67'
option ipaddr '198.100.100.1'
config interface 'wan'
option ifname 'eth0.2'
option proto 'dhcp'
option macaddr '04:a1:51:9a:03:68'
可以看出：eth0是有线网卡，eth0.1，eth0.2从上面通过switch虚拟出来，eth0.1对应LAN口，eth0.2对应WAN口，其地址都可以手动修改。
而radio0, radio1对应的是无线网卡（2.4G ,5G）
而br-lan是虚拟出来的，用于统一管理LAN
root@OpenWrt:/etc/config# brctl show
bridge name bridge id STP enabled interfaces
br-lan 7fff.04a1519a0367 no eth0.1
wlan1
wlan0
所以可以看出，eth0.2用于WAN口，其上一级的IP为：193.168.1.125；eth0.1用于管理LAN口，子LAN口的IP都由198.100.100.1进行分配。
（以上只是自己对网关很浅的一些认识，更多的可以关注下面引用的博客，并且诸如防火墙（firewall的设置可以参见：、etc/config 下面的firewall文件）））
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