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Zorluk: ZorIPv4 Static Routing

A Cisco router receives an IPv4 packet destined for host 192.168.50.45192.168.50.45. The router's routing table contains a static route `ip route 192.168.50.0 255.255.255.0 10.1.1.2` and a directly connected network 10.1.1.0/3010.1.1.0/30 out interface `GigabitEthernet0/1`. Arrange the sequential processing steps executed by the router to forward this packet from initial ingress lookup to egress transmission.

  1. 1Extract the destination IP address 192.168.50.45192.168.50.45 from the received packet header.
  2. 2Perform a routing table lookup for 192.168.50.45192.168.50.45 and identify the matching static prefix 192.168.50.0/24192.168.50.0/24 with next-hop IP 10.1.1.210.1.1.2.
  3. 3Perform a recursive lookup for next-hop IP 10.1.1.210.1.1.2 to determine the outbound interface `GigabitEthernet0/1`.
  4. 4Query the ARP table (or send an ARP request) to resolve the Layer 2 destination MAC address for 10.1.1.210.1.1.2.
  5. 5Encapsulate the IPv4 packet into a Layer 2 frame with the target MAC address and transmit it out interface `GigabitEthernet0/1`.

Cevap

The correct sequence is: Extract the destination IP address -> Perform primary routing lookup -> Perform recursive lookup for the next-hop IP -> Query ARP table for next-hop MAC -> Encapsulate packet and transmit out egress interface.
When a Cisco router receives an IP packet, it first extracts the destination IP address. Using longest prefix match, it matches the static route entry pointing to next-hop IP 10.1.1.2. Because this route specifies an IP next-hop rather than an outbound interface directly, the router performs a recursive lookup to find which connected interface reaches 10.1.1.2 (GigabitEthernet0/1). Knowing the egress Ethernet interface, it resolves the next-hop MAC address using ARP, encapsulates the IPv4 packet in an Ethernet frame, and transmits it out GigabitEthernet0/1.

Adım Adım Çözüm

1
Inspect destination header
Destination IPv4 address 192.168.50.45192.168.50.45 is extracted from the incoming frame.
Routing decisions are based on the packet's destination IPv4 address.
2
Execute primary route table lookup
Matches route `192.168.50.0 255.255.255.0` with next-hop IP 10.1.1.210.1.1.2.
The router uses longest prefix matching to select the route entry.
3
Execute recursive lookup
Resolves 10.1.1.210.1.1.2 to directly connected route 10.1.1.0/3010.1.1.0/30 on interface `GigabitEthernet0/1`.
Static routes configured solely with a next-hop IP address require a recursive lookup to identify the exit interface.
4
Resolve Layer 2 next-hop address
Obtains the target MAC address for 10.1.1.210.1.1.2 from the ARP table.
Ethernet encapsulation requires a destination Layer 2 MAC address for the next hop.
5
Encapsulate and egress
Frame is sent out `GigabitEthernet0/1`.
Final physical delivery step out the egress interface.

Anahtar Kavram

IPv4 Static Route Recursive Lookup & Packet Forwarding Pipeline
Tahmini Süre:2m 0s
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Konular

IPv4 Static Routing

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