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

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.

AMAC address of FF-FF-FF-FF-FF-FFis the Ethernetbroadcast address. When a switch receives a frame with this destination MAC address, it is required to forward the frame to all interfaces except the one it was received on.

Step-by-Step Breakdown:

Broadcast Frame Handling:When a frame with the broadcast MAC address is received, the switch will flood it out of all active ports that belong to the same VLAN as the incoming frame. The broadcast frame is not sent back out of the ingress interface (the interface where the frame was originally received).

Purpose of Flooding:Broadcasting is used to ensure that the frame reaches all devices within the broadcast domain (all devices within the same VLAN), which may not have a specific entry for the MAC address in their MAC address table.

Juniper Reference:

Layer 2 Frame Forwarding: Juniper switches flood broadcast frames to all ports in the same VLAN, except the port the frame was received on.

Filter-Based Forwarding (FBF) in Junos OS allows traffic to be routed based on specific criteria such as source address, rather than just the destination address. This is useful in scenarios like policy routing or providing multiple paths for different types of traffic.

Step-by-Step Breakdown:

Instance-Type Forwarding:You must create aninstance-type forwardingrouting instance. This routing instance allows for different routing tables based on the incoming packet filter.

Command:

set routing-instances FBF-instance instance-type forwarding

Match Filter:You need to create afilterto match the traffic that will be forwarded according to your custom routing policy. This filter is applied to an interface to determine which traffic will use the custom forwarding instance.

Command Example:

set firewall family inet filter FBF-filter term 1 from source-address