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Zorluk: ZorEncapsulation and De-encapsulation

A network administrator is performing packet flow analysis on a network where a host on Subnet A sends traffic to a server on Subnet B through an intermediate Layer 3 router. Which statement correctly describes the encapsulation and de-encapsulation actions executed by the router as it forwards a data packet toward its destination?

  1. The router strips the incoming Layer 2 frame header and trailer to inspect the Layer 3 IP packet destination, maintains the original IP packet payload, and encapsulates it inside a new Layer 2 frame with source and destination MAC addresses updated for the next hop.Cevap
  2. B
    The router de-encapsulates the packet through Layer 4 to inspect TCP port numbers before re-encapsulating the data into a brand-new IP packet and Ethernet frame.
  3. C
    The router strips both the Layer 2 Ethernet header and Layer 3 IP header, forwarding only the Layer 4 segment to the next switch for MAC address resolution.
  4. D
    The router modifies the destination IP address inside the Layer 3 header to match the next-hop router's physical MAC address while keeping the Layer 2 frame untouched.

Cevap

The router removes the incoming Layer 2 framing, inspects the Layer 3 IP header to determine the next hop, decrements the Time to Live (TTL), and encapsulates the preserved IP packet into a new Layer 2 frame with updated MAC addresses.
The correct response accurately highlights that Layer 3 routers strip incoming Layer 2 frame encapsulation to read the destination IP address, keep the IP packet intact for end-to-end delivery, and construct a new Layer 2 frame with updated source and destination hardware addresses for the outbound link.

Adım Adım Çözüm

1
Receive and process Layer 2 frame
The router interface receives the physical signals, validates the Frame Check Sequence (FCS), and strips the Layer 2 Ethernet header and trailer.
Layer 2 framing is hop-to-hop and only delivers data across the single local broadcast domain.
2
Inspect Layer 3 IP packet
The router reads the destination IP address from the IP header, decrements the Time to Live (TTL) field by 1, and recalculates the IP header checksum.
Logical end-to-end addressing resides at Layer 3 and governs route decision-making across subnet boundaries.
3
Re-encapsulate into new Layer 2 frame
The router queries ARP/neighbor discovery for the next-hop MAC address, encapsulates the IP packet into a new Layer 2 frame using its egress interface MAC as the source and the next-hop MAC as the destination, and sends the frame.
Data must be framed appropriately for the specific link layer protocol of the egress network interface.

Anahtar Kavram

Hop-by-Hop Layer 2 Re-framing vs End-to-End Layer 3 Packet Preservation
Tahmini Süre:2m 0s
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Konular

Encapsulation and De-encapsulation

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