Connecting a 2nd router

> I am planning to connect a 2nd router in order to connect a CCTV DVR
> to the 2nd Router. [...]

   That's not as clear as you might think.   Does this (unspecified) "a
CCTV DVR" use a wired or wireless network connection?

   You may or may not need some kind of gizmo where you want to put "a
2nd router", but it very likely wouldn't be configured as a
full-function router.  (Either some specialized extender, or a router
configured as something less capable than it could be.)

> [...] Drawing a ethernet cable from DVR to Router 1 is a challenge.
> [...]

   But that might make things much easier.  A pair of Powerline gizmos
might let you use your power wiring to emulate an Ethernet cable, with
less wall-piercing.

> The Router 1 is a ZTE 268A.

   ZTE ZXHN H268A?

   Having no CG3000-2STAUS to explore, and no useful manual to read, I'm
still relatively helpless on its details.

   If your (unspecified) "a CCTV DVR" has a (Ethernet) wired interface,
and you don't want to run a cable to it, then what you'd seem to want is
a wireless bridge.  For reference purposes, you might want to fetch a
User Manual for a different model, an R7000, and look in its User Manual
for "Set Up the Router in Bridge Mode".  If the picture there shows what
you want to do, then you could explore your CG3000v2 to see if has a
similar capability.  If not, then you may be able to find a cheap
wireless-bridge gizmo somewhere.

   If your (unspecified) "a CCTV DVR" has only a wireless interface,
then what you'd seem to want is a wireless extender, or, in the R7000
User Manual, look for "Set Up a Wireless Distribution System".  Again,
no bets on whether your CG3000v2 can do that, either.

   If you could run a cable (real or Powerline) to an Ethernet port on
the DVR, then you might need no additional gizmos at all.  If the DVR is
strictly wireless, and you could run a cable to its neighborhood, then
you ought to be able to configure the CG3000v2 as a wireless access
point (because that can be done with almost any wireless
(modem+)router).

> [...] then port forward the DVR to the Router 1, and then access the
> DVR on piblic internet. [...]

   If you can get the DVR connected to the LAN of the main router, then
the only remaining worry would be configuring port forwarding on the
main router.  I didn't find much useful info on a ZTE ZXHN H268A,
either, so I couldn't say if that's possible.