My router has dynamic DNS support through three services:

• DynDNS - Now owned by Oracle and a paid service.
• No-IP - It has a free tier with 1 hostname but sends you a confirmation email every month to make sure you're still using the address (which they can tell anyways if record is accessed and by pinging the IP so it's more like they want send you a monthly marketing reminder).
• TP-Link - This is the router company's one. You need a TP-Link ID which you have if you want to remote control your router.

I used TP-Link provider:

1. Login toTP-Link account then add a domain (enter anything, though it rejected my first couple of suggestions with invalid term and maybe it doesn't like www2 in www2-tgd-inc): dyn-tgd-inc.tplinkdns.com.
2. Delete the current A record for www2.tgd-inc.com.
3. Add a CNAME record for www2 that points to dyn-tgd-inc.tplinkdns.com.

Now if you do a DNS lookup:

% nslookup -debug www2.tgd-inc.com         
Server:		192.168.0.1
Address:	192.168.0.1#53

------------
    QUESTIONS:
	www2.tgd-inc.com, type = A, class = IN
    ANSWERS:
    ->  www2.tgd-inc.com
	canonical name = dyn-tgd-inc.tplinkdns.com.
	ttl = 7200
    ->  dyn-tgd-inc.tplinkdns.com
	internet address = 192.184.151.221
	ttl = 900
    AUTHORITY RECORDS:
    ADDITIONAL RECORDS:
------------
Non-authoritative answer:
www2.tgd-inc.com	canonical name = dyn-tgd-inc.tplinkdns.com.
Name:	dyn-tgd-inc.tplinkdns.com
Address: 192.184.151.221

In your web browser if you go to https://www2.tgd-inc.com:

1. Your computer does a DNS lookup for www2.tgd-inc.com
2. That response says lookup at dyn-tgd-inc.tplinkdns.com
3. Your computer does a DNS lookup for dyn-tgd-inc.tplinkdns.com
4. That response gives an IP address
5. Your browser goes that IP address and in URL bar it still says https://www2.tgd-inc.com so SSL certificate still works.

I rebooted the router, which picks up a new IP address. It took an hour or so for dyn-tgd-inc.tplinkdns.com to reflect the new IP address — you'd think the router knows the IP address changed so it should update immediately but still fast enough for home use.