I have Comcast service with 5 static IP addresses, using a Cisco DPC3939B as the cable modem. In addition to the 5 machines with static IP addresses, there are additional devices that get their IP addresses dynamically from the DPC3939B using DHCP.
Everything works as expected, except that we don't have connectivity from clients on the DHCP devices to servers on our static-IP machines.
Here are some details:
The static IP addresses assigned are A.B.C.209, A.B.C.210, A.B.C.211, A.B.C.212, and A.B.C.213. The Cisco gateway's IP address is A.B.C.214.
The devices using DHCP are assigned addresses of the form 10.1.10.x. The Cisco gateway's IP address on the DHCP LAN is 10.1.10.1.
So, for example, consider Machine 1 that uses DHCP and has IP address 10.1.10.19, and Machine 2 (running a server) that has static IP address A.B.C.212. Machine 1 cannot connect to a web server or ssh server on Machine 2.
(In contrast, connectivity to and from remote sites works just as I expected: both Machine 1 and Machine 2 can connect to remote servers on the Internet, and remote machines on the Internet can connect to Machine 2. Connectivity from one static-IP machine to another static-IP machine also works.)
I tried temporarily turning off all firewalls, but that didn't correct things, so it doesn't appear to be a firewall issue.
It doesn't make any difference if the machines are connecting over wifi or a hard-wired Ethernet connection; the results are the same.
Occasionally the connection appears to start to work, but very slowly (too slow to be usable at all) and only for a short while.
If I ping Machine 2 from Machine 1, sometimes all packets fail to get through, but sometimes some of the packets show results like:
Request timeout for icmp_seq 0 92 bytes from 10.1.10.1: Redirect Host(New addr: A.B.C.212) Vr HL TOS Len ID Flg off TTL Pro cks Src Dst 4 5 00 0054 91a8 0 0000 3f 01 8ad6 10.1.10.19 A.B.C.212
Comcast tech support thought that maybe I needed to set up a static routing table on the Cisco gateway, but that hasn't worked either (but maybe I just don't know how to set it up correctly).
Can anybody suggest what I could try so that our DHCP-based machines can talk to our machines with static IP addresses?