Starting from R12.8SP5 Access Gateway, the "server.conf" has the following change.
R12.8SP4
<Server> #General Server Information
#Define the listeners between #HTTP listener and proxy engine worker.ajp13.port=8009 worker.ajp13.host=localhost worker.shutdown.port=8005
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R12.8SP5/6
<Server> #General Server Information
#Define the listeners between #HTTP listener and proxy engine worker.ajp13.port=8009 worker.ajp13.host=::1 worker.shutdown.port=8005
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They are both listening on loopback address but one is ipv4 and another is ipv6.
So in case if you have explicitly disabled ipv6 on the server, probably due to hardening process, then the Proxy Engine can no longer listen on the specified address hence the error.
Following is a demonstration of ipv6 being disabled.
Before disabling IPv6
$ ifconfig -a ens192: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 inet 192.1.100.1 netmask 255.255.255.0 broadcast inet6 2001:db8::12:1 prefixlen 64 scopeid 0x20<link> ether 11:0c:29:b5:a4:xx txqueuelen 1000 (Ethernet) RX packets 4283589 bytes 3705255697 (3.4 GiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 2821941 bytes 1241545434 (1.1 GiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10<host> loop txqueuelen 1000 (Local Loopback) RX packets 1970997 bytes 12455630018 (11.6 GiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 1970997 bytes 12455630018 (11.6 GiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
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After disabling IPV6
[root@hostname ~]# sysctl -w net.ipv6.conf.all.disable_ipv6=1 net.ipv6.conf.all.disable_ipv6 = 1 [root@hostname ~]# sysctl -w net.ipv6.conf.default.disable_ipv6=1 net.ipv6.conf.default.disable_ipv6 = 1
[root@smps-02 ~]# ifconfig -a ens192: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 inet 192.1.100.1 netmask 255.255.255.0 broadcast ether 11:0c:29:b5:a4:xx txqueuelen 1000 (Ethernet) RX packets 4284067 bytes 3705440475 (3.4 GiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 2822301 bytes 1241724545 (1.1 GiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 loop txqueuelen 1000 (Local Loopback) RX packets 1971413 bytes 12455861332 (11.6 GiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 1971413 bytes 12455861332 (11.6 GiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
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As a result, "::1" cannot be used.
[root@smps-02 ~]# ssh ::1 ssh: connect to host ::1 port 22: Network is unreachable
[root@smps-02 ~]# ssh localhost The authenticity of host 'localhost (127.0.0.1)' can't be established. ECDSA key fingerprint is SHA256:ZHj3q5iSqxeRweBcqsarzdbUcu3APT7Gg1cvN8OXN6w. ECDSA key fingerprint is MD5:95:4a:c2:98:16:65:e1:ac:33:b4:f0:53:96:9f:da:ae. Are you sure you want to continue connecting (yes/no)? no
Host key verification failed.
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