JN0-280 Exam Dumps : Data Center, Associate (JNCIA-DC)

Thesource MAC addressin the Ethernet header is used to populate thebridging table(also called the MAC address table) on a switch. When a frame arrives at a switch, the switch examines the source MAC address and records it along with the ingress port in its MAC address table.

Step-by-Step Breakdown:

Learning Process:When an Ethernet frame arrives on a switch port, the switch looks at thesource MAC addressand adds this MAC address to the MAC table along with the port it was received on. This process is calledMAC learning.

Purpose:The switch uses this information to determine the correct port to send frames destined for that MAC address in future transmissions, thus ensuring efficient Layer 2 forwarding.

Juniper Reference:

Ethernet Switching: Juniper switches use source MAC addresses to build and maintain the MAC address table, which is essential for Layer 2 switching.

In the exhibit, theae0andae1interfaces are in alink downstate. This occurs when no physical interfaces (member interfaces) have been added to theLAG (Link Aggregation Group)interfaces, or the member interfaces are not operational.

Step-by-Step Breakdown:

LAG Configuration:ALAGinterface (aggregated Ethernet interface) is a logical interface that combines multiple physical interfaces for redundancy and increased bandwidth. The LAG will only be operational if at least one member interface is active and configured correctly.

No Operational Member Interfaces:If no member interfaces are added or if the member interfaces are down, the LAG will remain in adownstate, as shown in the exhibit for ae0 and ae1.

Resolution:Verify that physical interfaces have been added to the LAG using commands like:

LAG Interface Status: In Juniper, the link status of the LAG depends on its member interfaces, which must be operational for the LAG to function.

A trunk interface on a switch is used to carry traffic for multiple VLANs between switches or between a switch and another network device, like a router. Trunk interfaces use 802.1Q tagging to identify which VLAN the traffic belongs to.

Step-by-Step Breakdown:

Trunk Ports:

Trunk ports are typically used for inter-switch links or switch-to-router links where multiple VLANs need to be carried over the same physical connection.

VLAN traffic is tagged with a VLAN ID to ensure that it is properly identified as it crosses the trunk link.

802.1Q VLAN Tagging:

Trunk ports use 802.1Q to tag Ethernet frames with the VLAN ID. This ensures that frames are correctly forwarded to the appropriate VLANs on the other side of the trunk.

Juniper Reference:

Trunk Interface Configuration: In Juniper switches, trunk ports are configured to carry tagged traffic for multiple VLANs, which is essential for interconnecting multiple network segments.