Since this is not our case, we need to investigate further.
This is common on protocols for serial links such as PPP or HDLC.
In case the physical layer is up but the protocol is down, you are having a problem with the negotiation of protocol’s parameters. Only if the physical layer is up the protocol can be up, in any other case it will be down. up – The interface is receiving a signal (technically it closes the Tx/Rx loop).down – The interface is down, it does not receive any electric signal.administratively down – The interface is configured to be shut down with the shutdown command.There are three possible states for the Status field. Given that the switch is OK, we need to check the Status and the Protocol. When troubleshooting interface errors, it is unlikely to have a problem in the “OK?” field, as this means something very bad happened on the switch. Protocol – Indicates the data link layer status of the interfaceĪs you can imagine, we need to focus on three fields: OK?, Status and Protocol.Status – Indicates the physical layer status of the interface.
Method – Indicates how the interface obtained an IP address, it can be manual (statically configured from the administrator) or DHCP.OK? – Whether that interface is hardware OK on the switch (do not consider the cable/link, only the port).IP-Address – The IP address assigned to that interface, if any.Before we can draw a conclusion, we should explain the output of this powerful command. Look at the last two columns, they are both indicating “down”. We highlighted the interface connecting the hub. We are looking for the FastEthernet 0/24, the interface connecting the hub. Connect, jump into enable and then check the status of all interfaces with show ip interface brief. Given that, we cannot check anything on the hub, so we should check what’s wrong on the Left switch. In real-life, always prioritize the most impacting problem. Therefore, we can define this problem as more severe than others, even if we are talking about two users over a single one. The reason for that is simple: this problem is impacting more users. Even if this is not the first problem in our list, we should work on this before the others. Sometimes, you need to prioritize your work. It is time to start! Interface Troubleshooting step-by-step The link between SWL and Hub is down Since all of these are small issues, we will use a single ticket in our ticket-based troubleshooting approach.
In this lab, we are going to work with two switches, Left and Right (SWL, SWR), and a hub.