By default, all ports are untrusted when QoS is enabled. This means that any traffic received on these ports will not be trusted and will be subjected to the switch's QoS policies for classification and marking. This default behavior is intended to prevent any incoming traffic from being treated with higher priority or different QoS treatment without proper classification and assignment.

Edge-1 is unable to establish OSPF neighbor adjacency with ISP-1 due to an MTU mismatch. To resolve this, reduce the MTU on edge-1 to 1500 to match ISP-1's MTU. Additionally, you can configure the ip ospf mtu-ignore command on the edge-1 Gi0/0 interface to allow OSPF to establish adjacency despite the MTU mismatch.

Named ACLs (Access Control Lists) in networking are used to identify ACLs with a specific name rather than a number, making them easier to manage. They support both standard and extended ACLs, allowing for more flexibility and detailed traffic filtering.