Connectivity from machines on DHCP to machines with static IP addresses

​We have our Comcast cable modem (which is a Cisco ​​DPC3939B) set up so that some machines on our LAN have a static IP address, while other machines use DHCP (with dynamic IP addresses provided by the Cisco device).​

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​For some reason, we don't have connectivity from the devices which use DHCP to the devices which have static IP addresses.  (Clients on DHCP-connected machines can't access servers on static-IP machines.)​

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​Everything else works the way I expect:​

​- clients on all devices (both those with static IP addresses and those on DHCP) can connect to servers on the Internet;​

​- remote machines can connect to servers on our static IP addresses;​

​- clients on our machines with static IP addresses can access servers on our other machines with static IP addresses.​

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​Could anyone suggest what we need to do in our configuration so that clients on our DHCP-connected machines can connect to servers on our static-IP machines?  (If it matters, we only need connections on a few specific ports.)​

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​Thanks in advance for any help!​

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