Examkin

Soru

Zorluk: ZorRouting Concepts and Dynamic Routing Protocols

A Layer 3 core router receives an IP packet addressed to a remote destination host. Place the sequential evaluation and forwarding steps the router performs in the correct order from FIRST to LAST.

  1. 1Filter candidate routes in the Routing Information Base (RIB) to identify entries with the longest matching subnet mask (Longest Prefix Match).
  2. 2Compare the Administrative Distance (AD) among candidate routes that share the exact same longest prefix length to select the preferred routing source.
  3. 3Evaluate the routing metric among candidate routes from the same protocol sharing the same prefix length and AD to select the lowest-cost path.
  4. 4Install the winning route into the Forwarding Information Base (FIB) to map the destination prefix to an egress interface and next-hop IP address.
  5. 5Perform ARP/NDP lookup for the next-hop IP address, encapsulate the packet into a Layer 2 frame, and transmit it out the egress interface.

Cevap

The correct sequence for route evaluation and packet forwarding is: 1) Filter candidate routes by Longest Prefix Match (LPM), 2) Compare Administrative Distance (AD) for identical prefix lengths, 3) Evaluate internal routing metrics for tied protocols, 4) Install the optimal route into the Forwarding Information Base (FIB), and 5) Perform Layer 2 ARP resolution and frame encapsulation for transmission.
When a router processes a destination IP address, it follows a strict hierarchical order. First, it applies the Longest Prefix Match (LPM) rule, identifying routes with the most specific subnet mask. Next, if multiple candidate routes share the exact same prefix mask, it evaluates Administrative Distance (AD) to select the route from the most trustworthy routing source. If the tied candidate routes originate from the same routing protocol (having identical AD), the router compares their internal protocol metrics to select the path with the lowest cost. Once the best path is chosen, it is installed into the Forwarding Information Base (FIB) to map the next-hop IP and outbound interface. Finally, the router uses ARP or Neighbor Discovery to resolve the next-hop MAC address, rewrites the Layer 2 Ethernet frame header, and transmits the frame.

Adım Adım Çözüm

1
Evaluate prefix mask length across all RIB routes.
The route entry with the most specific matching prefix mask is selected.
Prefix length specificity always overrides administrative distance and metric during IP lookup.
2
Compare Administrative Distance (AD) for remaining tied paths.
The path learned from the routing source with the lowest AD value is selected.
AD measures source trustworthiness and resolves ties when prefix lengths match.
3
Compare routing metric among paths from the same protocol.
The candidate path with the lowest numerical metric is selected.
Metrics are protocol-specific cost values used for path selection within the same routing protocol.
4
Populate the Forwarding Information Base (FIB).
The destination prefix is associated with the selected outbound interface and next-hop address.
The FIB holds active forwarding decisions optimized for rapid hardware lookup.
5
Perform Layer 2 encapsulation and physical transmission.
ARP resolves the next-hop MAC address, the frame header is constructed, and the packet is forwarded.
Final packet delivery requires Layer 2 Ethernet framing using the next-hop MAC address.

Anahtar Kavram

Routing Decision Hierarchy and Forwarding Pipeline
Bu soruyu puanla

Konular

Routing Concepts and Dynamic Routing Protocols

Bu konudan daha fazla soru