System Architecture Flashcards

What is the Junos 'forwarding table' and how does it differ from the routing table?

Answer: The forwarding table (FIB) contains only active best routes optimized for hardware lookup; the routing table (RIB) contains all learned routes

The RIB (Routing Information Base) contains all learned routes from all protocols. The FIB (Forwarding Information Base) in the PFE contains only the active best routes programmed for hardware forwarding.

Which Junos platform is specifically designed for service provider edge routing with carrier-grade scalability?

Answer: MX Series

The MX Series is Juniper's Universal Edge Router platform designed for service provider applications, supporting massive scale for BGP, MPLS, L2/L3 VPNs, and subscriber management.

What does 'graceful restart' (GR) provide in Junos?

Answer: Allows routing protocol neighbors to maintain forwarding state during a planned Routing Engine restart, preventing route flaps

Graceful Restart allows a router undergoing a planned RE restart to signal its neighbors to maintain forwarding state and adjacency during the restart period, avoiding route withdrawals and reconvergence.

In Junos, what is a 'logical system'?

Answer: A virtualized partition of a physical Junos router that acts as an independent router with its own configuration, interfaces, and routing tables

Logical Systems (LSYS) divide a physical Junos device into multiple independent virtual routers, each with its own administrator, interfaces, protocols, and routing tables, used for multi-tenancy or lab environments.

What is the purpose of the Junos 'Enhanced Layer 2 Software' (ELS) feature set?

Answer: Provides a consistent CLI and configuration hierarchy for Layer 2 features across EX and QFX platforms

ELS standardizes the configuration syntax for Layer 2 features (VLANs, bridging, IRB, spanning tree) across Juniper EX and QFX switch platforms, replacing older platform-specific CLI.

Which Junos mechanism provides In-Service Software Upgrade (ISSU) capability?

Answer: ISSU requires dual Routing Engines and NSR/GRES to upgrade Junos software with minimal forwarding disruption

Junos ISSU leverages dual-RE architectures with GRES/NSR to upgrade software by upgrading the backup RE first, switching mastership, then upgrading the former primary, with minimal impact on forwarding.