The request system configuration rescue save command in Junos OS saves the most recently

committed configuration as the rescue configuration. This rescue configuration can be used to

recover the device if future configurations cause issues. It ensures there is a stable, known-good

configuration to fall back on, which is crucial in network management and troubleshooting.

Reference:

"rescue : save configurations as the rescue: request system configuration save .................( saves the

current configs as a rescue configs )" from Useful Juniper Commands.txt​​.

Juniper official documentation: Configuring and Activating a Rescue Configuration.

The Packet Forwarding Engine (PFE) is an integral component of Juniper Networks devices,

responsible for the data plane operations. The data plane, also known as the forwarding plane, is

where the actual processing and forwarding of packets occur based on the routing and forwarding

tables. The PFE executes the forwarding decisions made by the Routing Engine (RE), handling all

packet transmissions, including routing, filtering, and switching packets towards their destination.

This contrasts with the control plane operations handled by the RE, which involve routing table

maintenance, system management, and control protocol processing.

Referring to the exhibit, the presence of the "+" symbol next to the OSPF route for 192.168.100.2/32

indicates that this is the active route being used to forward traffic. The BGP route, although present,

does not have the "+" symbol, indicating it is not the active route. In Junos OS, the routing table

displays the active route with a "+" symbol, and the fact that the OSPF route has this symbol means it

is the preferred path based on the routing protocol's decision process, which takes into account

factors such as route preference (administrative distance) and metrics.

The transport layer in the OSI model is responsible for end-to-end communication and error

recovery. In a transport header, such as TCP or UDP, the key components include the source port

number and the destination port number. These port numbers are used to identify sending and

receiving applications. The source port number indicates the port of the sending application, and the

destination port number refers to the port of the receiving application. MAC addresses, on the other

hand, are part of the data link layer (Layer 2) and would be included in an Ethernet header, not a

transport header.

In the context of VLANs (Virtual Local Area Networks) on a Juniper switch, the numerical values

assigned to each VLAN, such as those for Prod, Test, and Dev, are known as VLAN tags. These tags are

part of the 802.1Q VLAN standard, which allows multiple VLANs to coexist on a single physical

network. Each tag uniquely identifies the VLAN to which a frame belongs, enabling the switch to

segregate and manage traffic based on VLAN membership. This tagging mechanism allows for

efficient traffic separation and management, ensuring that devices within one VLAN do not receive

traffic intended for another, thus maintaining network security and efficiency.

An Ethernet frame header includes the source MAC address (B) and the destination MAC address (D).

These addresses are used to deliver the frame from one Ethernet device to another directly

connected Ethernet device on the same network segment. Ethernet frames do not include IP

addresses, as those are part of the IP packet encapsulated within the Ethernet frame.

Two physical interface properties in Junos OS include the MAC address (A) and the Maximum

Transmission Unit (MTU) size (D). The MAC address is a hardware identifier for the network interface,

while the MTU size determines the largest packet size that the interface can transmit without

needing to fragment the packet.

Routing policies in Junos OS are crucial for controlling route advertisements and path selection. The

correct answers are B and C. An import routing policy for BGP determines which received prefix

advertisements are placed in the routing information base (RIB), and policy terms are evaluated from

top to bottom, with action taken on the first match found. This sequential evaluation allows for

precise control over routing decisions.

The Packet Forwarding Engine (PFE) in Junos OS performs several key functions, including

implementing firewall filters (A) and forwarding transit traffic (C). The PFE applies firewall filter rules

to incoming and outgoing traffic and is responsible for the high-speed forwarding of packets based

on the information in the forwarding table.

MAC (Media Access Control) addresses are unique identifiers assigned to network interfaces for

communications at the data link layer of a network segment. MAC addresses are used to identify the

physical hardware on a network. In the context of Ethernet switches, the destination MAC address in

incoming frames is used to determine the appropriate output port for forwarding the frame towards

its final destination. The switch does not change the destination MAC address; it uses the MAC

address to make forwarding decisions within the local network segment.