AnIRB (Integrated Routing and Bridging)interface provides routing functionality between VLANs at Layer 3, allowing devices in different VLANs to communicate with each other.

Step-by-Step Breakdown:

IRB Functionality:

The IRB interface enables routing between different VLANs by acting as a Layer 3 gateway. Traffic within the same VLAN is handled by Layer 2 switching, while traffic between VLANs is routed through the IRB interface.

Layer 3 Routing Between VLANs:

Each VLAN can be assigned an IP address on the IRB interface, which allows traffic to flow between VLANs based on Layer 3 IP routing.

Juniper Reference:

IRB Interface Configuration: Juniper supports IRB for inter-VLAN routing on devices like the EX and QFX series switches, facilitating Layer 3 communication in data centers.

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

When aMAC limiting violationoccurs on a Juniper switch, the switch will perform the following actions by default:

Step-by-Step Breakdown:

Port Disabled:When the number of MAC addresses on an interface exceeds the configured limit, the port isautomatically disabledto prevent further violations. This is a protective mechanism to prevent MAC address flooding.

Packet Dropped:Additionally, packets from the violating MAC address aredroppedto prevent any further communication from that address. This ensures that only valid MAC addresses are allowed to communicate through the interface.

Example Configuration:

set ethernet-switching-options secure-access-port interface mac-limit 5

If more than five MAC addresses are learned, the port is disabled, and excess packets are dropped.

Juniper Reference:

MAC Limiting: When the switch detects a MAC limiting violation, it disables the port and drops further packets from the violating MAC addresses to maintain network security.

In the exhibit, we see two next-hop addresses for the default static route (0.0.0.0/0):

The first next hop is172.25.11.254, with no specified preference.

The second next hop is172.25.11.200, with a specified preference of140.

Step-by-Step Breakdown:

Default Static Route Preference:If no preference is explicitly set for a next hop in Junos, it defaults to5for static routes.

Determining Preference:In this case, the next hop172.25.11.254does not have an explicit preference defined, so it will use the default value of5. The second next hop has a preference of140, which is higher,meaning it will only be used if the primary next hop is unavailable.

Juniper Reference:

Static Route Preference: In Junos, the default preference for static routes is5, and this value is applied unless overridden by the preference parameter.

EBGP (External BGP)andIBGP (Internal BGP)operate with different rules due to the nature of their relationships.

Step-by-Step Breakdown:

TTL Differences:

EBGP: By default, EBGP peers have a TTL of 1, meaning they must be directly connected, or the TTL needs to be manually increased for multihop EBGP.

IBGP: IBGP peers within the same AS have a TTL of 255, as they are expected to communicate over multiple hops within the AS.

Preference for EBGP Routes:

Routes learned viaEBGPare typically preferred over IBGP routes. This is because EBGP routes are considered more reliable since they originate outside the AS, while IBGP routes are internal.

Juniper Reference:

BGP Configuration: The different handling of TTL and route preferences between EBGP and IBGP ensures proper route selection and security within Junos-based networks.

AnIP fabricis a network architecture commonly used in data centers to provide scalable, high-throughput connectivity using aspine-leaf topology.

Step-by-Step Breakdown:

Layer 3 Routing Protocol:An IP fabric relies on aLayer 3 routing protocol, typically BGP or OSPF, to provide routing between the leaf and spine switches. This ensures efficient traffic forwarding across the network.

Single Connection Between Spine and Leaf:In an IP fabric, each leaf switch connects toevery spine switchwith a single connection. This ensures that traffic between any two leaf switches can travel through the spine layer in just two hops.

Juniper Reference:

Spine-Leaf Design: Juniper’s IP fabric implementations are designed for scalability and low-latency routing, often using protocols like BGP for Layer 3 control.

In Junos, thedefault export policyforOSPFis toreject all routesfrom being exported.

Step-by-Step Breakdown:

Default Export Policy:By default,OSPFin Junos does not export any routes to other routing protocols or neighbors. This is a safety mechanism to prevent unintended route advertisements.

Custom Export Policies:

If you need to export routes, you must create a customexport policythat explicitly defines which routes to advertise.

Example: You can create an export policy to redistribute static or connected routes into OSPF.

Juniper Reference:

OSPF Export Behavior: In Juniper devices, the default policy for OSPF is to reject route advertisements unless explicitly configured otherwise through custom policies.