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Zorluk: OrtaIPv4 Static Routing

An engineer configures a next-hop IPv4 static route on a Cisco router using the command `ip route 10.1.2.0 255.255.255.0 192.168.12.2`. Place the processing steps in the correct sequential order from first to last that the router performs when forwarding an incoming packet destined for 10.1.2.4510.1.2.45.

  1. 1The router performs a longest-prefix match lookup in the routing table for destination 10.1.2.4510.1.2.45 and matches the static route entry pointing to next-hop 192.168.12.2192.168.12.2.
  2. 2The router conducts a recursive lookup in the routing table for next-hop address 192.168.12.2192.168.12.2 to determine the egress interface.
  3. 3The router consults the ARP table to resolve the Layer 2 MAC address associated with next-hop address 192.168.12.2192.168.12.2.
  4. 4The router encapsulates the IPv4 packet into a Layer 2 frame and transmits it out the egress interface toward the next-hop destination.

Cevap

The correct sequence for packet forwarding with a next-hop static route is: First, match the packet destination IP 10.1.2.4510.1.2.45 to the static route entry pointing to next-hop 192.168.12.2192.168.12.2. Second, perform a recursive lookup in the routing table for 192.168.12.2192.168.12.2 to find the outgoing interface. Third, look up the MAC address of 192.168.12.2192.168.12.2 in the ARP table. Fourth, encapsulate the packet into a Layer 2 frame and transmit it out the egress interface.
When a static route specifies only a next-hop IPv4 address (recursive static route), the router must first identify the static route via longest-prefix match. Next, it performs a recursive RIB lookup on the next-hop IP address to determine the exit interface. After identifying the exit interface, it performs an ARP table lookup to find the next-hop MAC address, and finally encapsulates and transmits the frame.

Adım Adım Çözüm

1
Evaluate incoming packet destination IP against routing table entries.
The destination address 10.1.2.4510.1.2.45 matches static route 10.1.2.0/2410.1.2.0/24 with next-hop 192.168.12.2192.168.12.2.
Routing decisions begin with a longest-prefix match lookup in the RIB.
2
Perform recursive routing lookup for next-hop IP address 192.168.12.2192.168.12.2.
The router identifies the directly connected network prefix and egress interface used to reach 192.168.12.2192.168.12.2.
Static routes configured solely with a next-hop IP require a recursive lookup to identify the exit interface.
3
Resolve Layer 2 destination hardware address via ARP cache lookup for 192.168.12.2192.168.12.2.
The target next-hop MAC address is retrieved for frame header construction.
Ethernet interfaces require the next-hop MAC address to format the data-link layer encapsulation.
4
Encapsulate IPv4 packet into Layer 2 Ethernet frame and send out the egress interface.
The packet is transmitted on the physical wire.
All forwarding requirements (interface and Layer 2 rewrite info) are complete.

Anahtar Kavram

IPv4 Static Route Recursive Lookup & Forwarding Process
Tahmini Süre:1m 30s
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Konular

IPv4 Static Routing

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