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

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.

In the exhibit, the BGP routes are marked ashidden. This typically happens when the routes are not considered valid for use, but they remain in the routing table for reference. One common reason for BGP routes being hidden is that thenext hopfor these routes is unreachable.

Step-by-Step Breakdown:

BGP Next Hop:In BGP, when a route is received from a neighbor, thenext hopis the IP address that must be reachable for the route to be used. If the next hop is unreachable (i.e., the router cannot find a path to the next-hop IP), the route is marked as hidden.

Analyzing the Exhibit:The exhibit shows that the BGP next hop for all hidden routes is 10.4.4.4. If this IP is unreachable, the BGP routes from that neighbor will not be considered valid, even though they appear in the routing table.

Verification:

Use the command show route 10.4.4.4 to check if the next-hop IP is reachable.

If the next-hop is not reachable, the BGP routes will be hidden. Resolving the next-hop reachability issue (e.g., fixing an IGP route or an interface) will allow the BGP routes to become active.

Juniper Reference:

Junos Command: show route hidden displays routes that are not considered for forwarding.

Troubleshooting: Check the next hop reachability for hidden BGP routes using show route .

In OSPF, routers exchange link-state information in different stages to establish full adjacency. TheMTU sizeis checked during theExchangestate.

Step-by-Step Breakdown:

OSPF Adjacency Process:

OSPF routers go through multiple stages when forming an adjacency:Down,Init,2-Way,ExStart,Exchange,Loading, andFull.

Exchange State:

During theExchangestate, OSPF routers exchangeDatabase Description (DBD)packets to describe their link-state databases. TheMTU sizeis checked at this stage to ensure both routers can successfully exchange these packets without fragmentation.

If there is anMTU mismatch, the routers may fail to proceed past the Exchange state.

Juniper Reference:

MTU Checking in OSPF: Junos uses the Exchange state to check for MTU mismatches, ensuring that routers can properly exchange database information without packet fragmentation issues.