First of all, do a show running-config interface GigabitEthernet 1/0/X and have a look at how those interfaces are actually configured.

Then do what is needed:


If they are in shutdown state, issue a no shutdown command.
If they are not in the right VLAN, issue a switchport access vlan X command.
If they are configured for something else than standard access (i.e. trunking), clear their configuration and reconfigure them.


How to Enable Ports 25 - 28 on a Cisco Catalyst 3750
I'm looking at a problem in my textbook and it says:

Let $ψ : G_1 → G_2$ be a surjective group homomorphism. Let $H_1$ be a normal subgroup of $G_1$ and suppose that $ψ(H_1) = H_2$. Prove or disprove that $G_1/H_1$ is isomorphic $G_2/H_2$.

So far, I know that since $H_1$ is normal in $G_1$, $H_2$ is also normal in $G_2$. I'm unsure how to proceed from here though, can someone give me a hint?
