localhost与本机IP IPtables匹配顺序

localhost&host IPtables

iptables链匹配顺序

ping localhost

• 当前实验网络为IPV4模式
• 通过tcpdump抓包，我们可以发现ping localhost的流量最终发送到lo网卡了
• 通过iptables pkts数据计数我们可知，ping localhost的iptables过滤流程为：应用程序->OUTPUT->POSTROUTING(路由决策到lo网卡)->lo网卡(处理完成后)->PREROUTING(路径决策到本地)->INPUT->应用程序，由此可见我们针对localhost做一些防火墙规则是会生效的
• ping 127.0.0.1和ping localhost效果一致，这里不做测试了

# 查看本地网卡列表
[root@localhost ~]# ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: ens160: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:0c:29:82:82:e5 brd ff:ff:ff:ff:ff:ff
    altname enp2s0
    inet 192.168.0.21/24 brd 192.168.0.255 scope global noprefixroute ens160
       valid_lft forever preferred_lft forever
   
# 设置iptables规则，用于记录icmp流量
	iptables -t raw -A PREROUTING -p icmp -j ACCEPT
	iptables -t raw -A OUTPUT -p icmp -j ACCEPT
	iptables -t mangle -A INPUT -p icmp -j ACCEPT
	iptables -t mangle -A POSTROUTING -p icmp -j ACCEPT

# 一个窗口ping localhost: ping -c 1 localhost,我们抓去lo网卡流量，可见有icmp相关数据报文
[root@localhost ~]# tcpdump -i lo -Nnnvl icmp6 or icmp
dropped privs to tcpdump
tcpdump: listening on lo, link-type EN10MB (Ethernet), snapshot length 262144 bytes
07:24:23.690903 IP6 (flowlabel 0xe1051, hlim 64, next-header ICMPv6 (58) payload length: 64) ::1 > ::1: [icmp6 sum ok] ICMP6, echo request, id 2, seq 1
07:24:23.690938 IP6 (flowlabel 0xfcb2c, hlim 64, next-header ICMPv6 (58) payload length: 64) ::1 > ::1: [icmp6 sum ok] ICMP6, echo reply, id 2, seq 1
^C
2 packets captured
4 packets received by filter
0 packets dropped by kernel

# 查看raw 表规则
[root@localhost ~]# iptables -t raw -nvL
Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
    2   168 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0           

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
    2   168 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0
    
# 查看mangle表规则
[root@localhost ~]# iptables -t mangle -nvL
Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
    2   168 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0           

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
    2   168 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0 
 
# 清空iptables规则
	iptables -t raw -F
	iptables -t mangle -F

Ping 本机地址

• 由于ping本机地址，数据报文最终也被送到lo网卡了，其iptables过滤顺序和ping localhost一致，这里不重复分析了

# 查看网卡列表
	同上面网络信息

# 一个窗口ping localhost: ping -c 1 192.168.0.10,我们抓ens160和lo网卡，可见数据报文还是去lo网卡了
[root@localhost ~]# ping 192.168.0.21 -c 1
ping: socket: Address family not supported by protocol
PING 192.168.0.21 (192.168.0.21) 56(84) bytes of data.
64 bytes from 192.168.0.21: icmp_seq=1 ttl=64 time=0.090 ms

--- 192.168.0.21 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.090/0.090/0.090/0.000 ms

[root@localhost ~]# tcpdump -i ens160 icmp -Nnnvl
dropped privs to tcpdump
tcpdump: listening on ens160, link-type EN10MB (Ethernet), snapshot length 262144 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

[root@localhost ~]# tcpdump  -i lo icmp -Nnnvl
dropped privs to tcpdump
tcpdump: listening on lo, link-type EN10MB (Ethernet), snapshot length 262144 bytes
21:51:04.409541 IP (tos 0x0, ttl 64, id 37837, offset 0, flags [DF], proto ICMP (1), length 84)
    192.168.0.21 > 192.168.0.21: ICMP echo request, id 4, seq 1, length 64
21:51:04.409557 IP (tos 0x0, ttl 64, id 37838, offset 0, flags [none], proto ICMP (1), length 84)
    192.168.0.21 > 192.168.0.21: ICMP echo reply, id 4, seq 1, length 64
^C
2 packets captured
4 packets received by filter
0 packets dropped by kernel