无法 telnet 到私有 IP 或端口

Question

需要进行哪些特定更改，以便本地 IP 上的 CentOS 7 安装192.168.1.6可以telnet到另一个本地 IP上的CentOS 7 安装192.168.1.5？

如您所见，可以192.168.1.6PING192.168.1.5如下：

[root@localhost /]# ping 192.168.1.5
PING 192.168.1.5 (192.168.1.5) 56(84) bytes of data.
64 bytes from 192.168.1.5: icmp_seq=1 ttl=64 time=0.515 ms
64 bytes from 192.168.1.5: icmp_seq=2 ttl=64 time=0.565 ms
^C
--- 192.168.1.5 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1000ms
rtt min/avg/max/mdev = 0.515/0.540/0.565/0.025 ms

但telnetFROM 192.168.1.6TO192.168.1.5失败如下：

[root@localhost /]# telnet 192.168.1.5
Trying 192.168.1.5...
telnet: connect to address 192.168.1.5: No route to host

并且telnetFROM 192.168.1.6TO port 5432at192.168.1.5也失败如下：

[root@localhost /]# telnet 192.168.1.5:5432
telnet: 192.168.1.5:5432: Name or service not known
192.168.1.5:5432: Unknown host
[root@localhost /]#

PostgreSQL 正在运行192.168.1.5，并且应该正在接收telnet 192.168.1.5:5432. 因此，我pg_hba.conf在运行上述代码之前添加了以下行：

host    all    all    192.168.1.6/24    trust

我在运行上述之前ping并telnet通过键入systemctl restart postgresql.

同样，在运行上述ping和telnet命令之前，我还在 上创建了以下防火墙规则192.168.1.5：

[root@localhost ~]# firewall-cmd --zone=public --add-port=5432/tcp
[root@localhost ~]# firewall-cmd --permanent --zone=trusted --add-source=192.168.1.6/32
[root@localhost ~]# firewall-cmd --reload  

另外，我确认 PostgreSQL 正在运行，port 5432在 的终端中键入以下命令192.168.1.5：

[root@localhost ~]# ss -l -n | grep 5432
u_str  LISTEN     0      128    /var/run/postgresql/.s.PGSQL.5432 71466                 * 0
u_str  LISTEN     0      128    /tmp/.s.PGSQL.5432 71468                 * 0
tcp    LISTEN     0      128    127.0.0.1:5432                  *:*
tcp    LISTEN     0      128     ::1:5432                 :::*
[root@localhost ~]#

---

@roaima 的建议：

---

根据@roaima 的建议，我尝试了以下操作，但仍然无法连接：

从 192.168.1.6，我发送了：

[root@localhost ~]# telnet 192.168.1.5 5432
Trying 192.168.1.5...
telnet: connect to address 192.168.1.5: No route to host

而在 192.168.1.5 上，请求tcpdump的接收端telnet是：

[root@localhost ~]# tcpdump -i eth0 port 5432 or arp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
16:52:49.309526 IP 192.168.1.6.53328 > localhost.localdomain.postgres: Flags [S], seq 3210933916, win 29200, options [mss 1460,sackOK,TS val 629624820 ecr 0,nop,wscale 7], length 0
16:52:54.312716 ARP, Request who-has localhost.localdomain tell 192.168.1.6, length 28
16:52:54.312750 ARP, Reply localhost.localdomain is-at 52:54:00:ef:35:18 (oui Unknown), length 28
^C
3 packets captured
4 packets received by filter
0 packets dropped by kernel  

同样，从 192.168.1.6 我仅将以下 telnet 发送到 IP 级别：

[root@localhost ~]# telnet 192.168.1.5
Trying 192.168.1.5...
telnet: connect to address 192.168.1.5: No route to host
[root@localhost ~]#

而在 192.168.1.5 上，请求tcpdump的接收端telnet是：

[root@localhost ~]# tcpdump -i eth0 port 5432 or arp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
//THESE 2 LINES PRINTED BEFORE 2ND TELNET WAS RUN: 16:58:11.619638 ARP, Request who-has gateway tell localhost.localdomain, length 28
//THESE 2 LINES PRINTED BEFORE 2ND TELNET WAS RUN: 16:58:11.619940 ARP, Reply gateway is-at b8:ec:a3:11:74:6e (oui Unknown), length 46
16:58:35.555570 ARP, Request who-has 192.168.1.6 tell localhost.localdomain, length 28
16:58:35.555753 ARP, Reply 192.168.1.6 is-at 52:54:00:ab:31:40 (oui Unknown), length 28
^C
4 packets captured
4 packets received by filter
0 packets dropped by kernel
[root@localhost ~]#  

---

@cutrightjm 的建议：

---

在 上192.168.1.5，我在一次 Putty 会话中输入了以下内容：

[root@localhost ~]# telnet localhost 5432
Trying ::1...
Connected to localhost.
Escape character is '^]'.

同时，在单独的 Putty 会话中192.168.1.5，我没有看到 的结果tcpdump，如下所示：

[root@localhost ~]# tcpdump -i eth0 port 5432 or arp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel
[root@localhost ~]#

---

@JeffSchaller 的建议：

---

根据@JeffSchaller 的建议，我在192.168.1.6. 请注意，这是 CentOS 7，已替换netstat为ss，并已替换iptables为firewalld：

ss -rn生产了 90 行输出。你能建议一个有意义的grep或其他过滤器来减少输出到允许添加到发布的数量吗？

[root@localhost ~]# iptables -Ln
iptables: No chain/target/match by that name.


[root@localhost ~]# firewall-cmd --list-all
public (active)
  target: default
  icmp-block-inversion: no
  interfaces: eth0
  sources:
  services: dhcpv6-client ssh
  ports: 8080/tcp
  protocols:
  masquerade: no
  forward-ports:
  sourceports:
  icmp-blocks:
  rich rules:

[root@localhost ~]#

我还在上运行了以下命令192.168.1.6：

[root@localhost ~]# ip route
default via 192.168.1.1 dev eth0  proto static  metric 100
192.168.1.0/24 dev eth0  proto kernel  scope link  src 192.168.1.6  metric 100

[root@localhost ~]# ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1
    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
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 52:54:00:ab:31:40 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.6/24 brd 192.168.1.255 scope global dynamic eth0
       valid_lft 133013sec preferred_lft 133013sec
    inet6 fe80::5054:ff:feab:3140/64 scope link
       valid_lft forever preferred_lft forever
[root@localhost ~]#

---

删除两台机器上的防火墙

---

作为一个极端的测试，我删除了两个防火墙192.168.1.5，并192.168.1.6通过打字yum remove firewalld和yum remove iptables在两台机器上。然后我按如下方式验证了两个删除：

在192.168.1.5：

[root@localhost ~]# systemctl status firewalld
Unit firewalld.service could not be found.
[root@localhost ~]# iptables -L -n
-bash: /sbin/iptables: No such file or directory

在192.168.1.6：

[root@localhost ~]# systemctl status firewalld
Unit firewalld.service could not be found.
[root@localhost ~]# iptables -L -n
-bash: /sbin/iptables: No such file or directory

接下来，我输入tcpdump -i eth0 port 5432 or arp上192.168.1.5，接着打字telnet 192.168.1.5 5432上192.168.1.6。

telnet 的结果是打印了以下拒绝消息192.168.1.6：

[root@localhost ~]# telnet 192.168.1.5 5432
Trying 192.168.1.5...
telnet: connect to address 192.168.1.5: Connection refused
[root@localhost ~]#

同时，来自电话的tcpdump打印输出是： 192.168.1.5telnet1.6

[root@localhost ~]# tcpdump -i eth0 port 5432 or arp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
10:25:11.349238 ARP, Request who-has localhost.localdomain tell gateway, length 46
10:25:11.349261 ARP, Reply localhost.localdomain is-at 52:54:00:ef:35:18 (oui Unknown), length 28
10:25:14.391222 IP 192.168.1.6.53344 > localhost.localdomain.postgres: Flags [S], seq 3043089625, win 29200, options [mss 1460,sackOK,TS val 692769902 ecr 0,nop,wscale 7], length 0
10:25:14.391265 IP localhost.localdomain.postgres > 192.168.1.6.53344: Flags [R.], seq 0, ack 3043089626, win 0, length 0
10:25:19.395578 ARP, Request who-has 192.168.1.6 tell localhost.localdomain, length 28
10:25:19.396039 ARP, Reply 192.168.1.6 is-at 52:54:00:ab:31:40 (oui Unknown), length 28
^C
6 packets captured
6 packets received by filter
0 packets dropped by kernel
[root@localhost ~]#

为了确定 PostgreSQL 是否正在侦听port 5432，我在 上键入了以下两个命令192.168.1.5：

请注意，在运行以下命令时，firewalld和iptables仍然会被删除：

首先，我查看了该pg_hba.conf文件192.168.1.5以查看是否存在值得信任的规则192.168.1.6：

[root@localhost ~]# vi /var/lib/pgsql/data/pg_hba.conf
# LOTS OF # COMMENTED LINES OMITTED HERE FOR BREVITY
# TYPE  DATABASE        USER            ADDRESS                 METHOD

# "local" is for Unix domain socket connections only
local   all             all                                     trust
# IPv4 local connections:
host    all             all             127.0.0.1/32            trust
host    all             all             192.168.1.6/24          trust
# IPv6 local connections:
host    all             all             ::1/128                 trust

接下来，我输入以下netstat命令192.168.1.5来查看是否有以下规则port 5432：

[root@localhost ~]# netstat -anpt | grep LISTEN
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      943/sshd
tcp        0      0 127.0.0.1:5432          0.0.0.0:*               LISTEN      25166/postgres
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      1483/master
tcp6       0      0 127.0.0.1:45228         :::*                    LISTEN      19089/java
tcp6       0      0 127.0.0.1:8020          :::*                    LISTEN      14338/java
tcp6       0      0 :::7990                 :::*                    LISTEN      19089/java
tcp6       0      0 :::22                   :::*                    LISTEN      943/sshd
tcp6       0      0 ::1:5432                :::*                    LISTEN      25166/postgres
tcp6       0      0 127.0.0.1:7992          :::*                    LISTEN      19066/java
tcp6       0      0 ::1:7992                :::*                    LISTEN      19066/java
tcp6       0      0 ::1:25                  :::*                    LISTEN      1483/master
tcp6       0      0 127.0.0.1:36122         :::*                    LISTEN      19089/java
tcp6       0      0 :::8095                 :::*                    LISTEN      14338/java
tcp6       0      0 :::5701                 :::*                    LISTEN      19089/java
[root@localhost ~]#

Answer 1

第一个问题是您对telnet命令使用了错误的语法。运行man telnet会告诉你语法是这样的：

telnet <host> [<port>]

所以在你的情况下，你应该运行这个：

telnet 192.168.1.5 5432

第二个问题是，您在每台主机上都有一个防火墙规则，以防止到 5432/tcp 的出站流量。（也可能是其他的端口也是。）错误信息，“到主机的路由”，由产生iptables --j REJECT该规则OUTPUT具有链--reject-with icmp-host-prohibited。以下是创建此类规则的示例：

iptables -I OUTPUT -p tcp --dport 5432 -j REJECT --reject-with icmp-host-prohibited

这满足了路由明确存在的情况，因为ping成功了，但你的telnet会话失败了。您自己可以使用命令iptables --line-numbers -nvL（不是iptables -Ln，它试图列出链的规则n）来检查这一点。

确认流量确实可以建立的两个临时修复是

• 完全禁用两个系统上的防火墙

• 在两个系统上运行这两个命令（您可以通过替换-I为之后删除它们-D）

  iptables -I INPUT -p tcp --src 192.168.1.5/30 -j ACCEPT
  iptables -I OUTPUT -p tcp --dst 192.168.1.5/30 -j ACCEPT
  

我（还）不够熟悉 CentOS 7 防火墙工具，无法为您提供完整的解决方案。我可以去挖掘，或者其他人可能想编辑此答案以提供该信息。