Difference between "show interface" and "show ethernet-switching table" commands in Juniper switches

In Juniper switches running Junos OS, the commands show interface and show ethernet-switching table are used to retrieve different types of information related to the network interfaces and Layer 2 (Ethernet) switching behavior. Here's a detailed comparison of the two commands:

1. show interface Command

The show interface command is used to display detailed information about the physical and logical interfaces on a Juniper device. It provides information such as interface status, operational metrics, and configuration details.

What you get with show interface:

• Interface Status: Whether the interface is up or down.
• Interface Configuration: IP address, MTU size, encapsulation type, and other configuration settings for Layer 3 interfaces.
• Traffic Statistics: Ingress and egress packet counts, error statistics, and other performance-related metrics.
• Interface Settings: Details like link speed, duplex mode, and whether the interface is administratively up or down.
• Errors and Drops: Information about packet drops, CRC errors, or other issues on the interface.

Example Output:

user@switch> show interfaces ge-0/0/0
Physical interface: ge-0/0/0, Enabled, Physical link is Up
  Interface index: 93, SNMP ifIndex: 524
  Link-level type: Ethernet, MTU: 1514, Speed: 1000mbps, Duplex: Full-Duplex
  Input packets: 123456789, Output packets: 987654321, Errors: 0
  Input bytes: 1000000000, Output bytes: 500000000

This command provides detailed operational statistics about the physical interface itself, including packet counts, errors, speed, and more.

2. show ethernet-switching table Command

The show ethernet-switching table command is used to display the MAC address table (also known as the forwarding table or bridge table) on a Juniper switch. This table contains the mappings of MAC addresses to the specific ports or VLANs where those MAC addresses are reachable. It’s crucial for Layer 2 Ethernet switching, as the switch uses the MAC address table to forward frames based on the destination MAC address.

What you get with show ethernet-switching table:

• MAC Address Entries: The table lists MAC addresses that the switch has learned.
• VLAN Association: The VLAN in which the MAC address is located.
• Port Information: The physical interface (or virtual interface) associated with each MAC address.
• Age of Entries: How long the MAC address has been in the table before it ages out or is refreshed.
• Dynamic or Static Entries: Whether the MAC address was dynamically learned or manually configured (static entries).

Example Output:

user@switch> show ethernet-switching table
MAC address           Type           VLAN    Interface       Age
00:11:22:33:44:55     Dynamic        100     ge-0/0/0       00:02:10
00:66:77:88:99:00     Dynamic        200     ge-0/0/1       00:03:15
00:AA:BB:CC:DD:EE     Static         100     ge-0/0/2       Permanent

This output shows the MAC addresses, the VLAN they belong to, the interface (port) where the MAC address was learned, and how long the entry has been in the table.

Key Differences

Summary:

• show interface is used to gather information about the operational status and statistics of individual interfaces, including layer 1 and 3 details (such as link status, IP addresses, and traffic counters).
• show ethernet-switching table provides the Layer 2 forwarding table, showing how MAC addresses are mapped to switch ports and VLANs, which is key for troubleshooting Ethernet switching and frame forwarding.