Temporary slow network. What to look for in a capture?

A customer beleives that they are having network problems. I want to make a capture from a mirrored port on a switch.

How can I see the following in a capture:

- if a switch port is bad?
- if a host have a bad network interface? Bad driver? Wrong speed settings 10/100 half/full Auto and so on?
- if a host are broadcasting (why would it do that?)

Im a beginner on this so please help me on what to look for.
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I would look for
1. broadcasts,
2. network scans (it is virus)
3. broken packets and therefore a lot of retransmits

I would also look at logs on switches and firewall
TANGLADAuthor Commented:
I now how to look for broadcasts in a capture. But how do I see network scans and retransmits in a capture?
network scans - just look for patterns, for example it is strange when a single pc is sending out a lot of arp who has requests for the ips not in your subnet
retransmits and broken packets are marked with red in wireshark

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Network Analysis

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