a) Loop can't occure on a single cable, of course.
b) It is NOT a bad thing, the only dangerous portfast feature is a possibility of a very-short-time loop in the case you connect two portfast-enabled ports into one hub, e.g. But the switch is still sending BPDUs on portfast ports, so even in that case loop will be disconnected after first BPDU received (2 sec default).
So I think there is no problem with portfast on port connecting a router.
But you are saying "STP is disabled, which means all of the ports are in portfast mode". Have you really disabled STP on the switch or have you just enabled portfast on all ports (i.e. STP is still running)? I would be afraid of disabling STP on the switch, this is really dangerous.
An admin at a previous job decided to turn off STP to save the bandwidth consumed by STP generated packets flying around every 2 seconds. Since the network was designed without any redundant links, STP was not needed.
Until . . .
One day a tech plugged a cable from one switch to another. Why? I have no idea. But, it brought the entire network to its knees until we found this long cable running down the hall.
The admin's respose was - don't do that.
I agree - turning off STP can have some severe unintended consequences - at the most unfortunate time.
We are pleased to announce availability of Beta software for 16.6.3.
16.6.3 will be the second rebuild on the 16.6 release train targeted
towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are
looking for early feedback from customers befor...
Introduction Featured Speakers Luis Espejel is the Telecommunications
Manager of IENova, an Oil & Gas company. Currently he works with Cisco
IOS® and Cisco IOS XE platforms, and NX to some extent. He has also
worked as a Senior Engineer with the Routing P...
In this session you can learn more about Layer 3 multicast and the best
practices to identify possible threats and take security measures. It
provides an overview of basic multicast, the best security practices for
use of this technology, and recommendati...