show interfaces status - Lists the interface status.For LAN switch interfaces, both codes typically have the same value, either “up” or “down.” These generally indicate whether Layer 1 is working (line status) and whether Layer 2 is working (protocol status). Show interfaces and show interfaces description - These commands list the line status and protocol status.Both sets of status codes can determine whether an interface is working. Show Interfaces Command and Interface Status CodesĬisco switches use two different sets of interface status codes. You can use any port number from 1 to 65535 to test whether a remote device is listening to the specific port, for example, telnet 172.17.5.74 8080. When you use Telnet to connect to a remote device, it uses the default port (23). You can also use an extended traceroute command to test connectivity from a specified source - for example, traceroute 10.10.60.6 source Loopback0. Therefore, you can traceroute to test the path that packets chose to move to their destination. This process continues until the packet reaches the final destination and receives a “port unreachable” ICMP message. Then traceroute sends a set of three UDP datagrams with TTL 2, so they time out when they hit the second router, causing it to responds with timeout message. Traceroute works by sending remote host a sequence of three UDP datagrams with a TTL of 1 in the IP header this causes the datagram to time out when it hits the first router on the path, causing the router to respond with an “ICMP time exceeded” message. Traceroute is a function that traces the path from one network to another, so it can help diagnose the source of many problems. You can ping from the particular interface by adding the source parameter with the interface name at the end of the command - for example, ping 172.17.4.6 source Ethernet 0/0. No reply was received within the timeout period. ! - An ICMP echo reply packet was received within the timeout period (2 seconds, by default)
This command sends an Internet Control Message Protocol (ICMP) echo request and displays one of the following: In order to troubleshoot a device for these properties, we need to use specify the IP address of the device - for example, ping 172.17.4.6. The basic purpose for ping is to check for reachability, round trip time (RTT) and packet loss.
Of course, being able to discover a lot of information about neighboring devices is a network security exposure.
To get additional details, such as the full name of the model of switch and the IP address configured on the neighboring device, add the detail parameter as follows: show cdp neighbors detail This interface command also lists the platform, identifying the specific model of the neighboring router or switch.
Each line provides the most important topology information about the neighbor: its hostname (device ID), the local device’s interface, and its interface (under the Port heading). This command lists each neighboring device, one per line. To see this information, use the show cdp command: show cdp neighbors Platform: The IOS version running on the device.Capabilities list: Device type (for example, router or switch).Port identifier: The interface on the remote device that sent the CDP advertisement.Address list: Network and data link addresses.CDP discovers several useful details from neighboring Cisco devices: Therefore, Cisco hardware that supports CDP can learn about other devices by listening for these messages. This is possible because Cisco routers and switches routinely send out CDP messages that announce information about themselves. The Cisco Discovery Protocol (CDP) discovers basic information about neighbor routers and switches without needing to know the passwords for those Cisco network devices. Let’s review them and see which issues they can help you investigate. There are various tools that can help with network troubleshooting.