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Difficulty: MediumRouting Table Components

An administrator executes the `show ip route` command on a Cisco enterprise router, resulting in the following partial routing table output:

text
Codes: C - connected, S - static, O - OSPF, D - EIGRP

Gateway of last resort is not set

10.250.0.0/16 is variably subnetted, 4 subnets, 4 masks
O 10.250.16.0/20 [110/20] via 192.168.1.2, 00:14:22, GigabitEthernet0/0
D 10.250.16.0/24 [90/307200] via 192.168.1.6, 00:05:10, GigabitEthernet0/1
S 10.250.16.128/26 [1/0] via 192.168.1.10
C 10.250.16.128/27 is directly connected, GigabitEthernet0/2

Which two statements accurately describe how the router interprets these components and forwards traffic? (Select two.)

  1. A packet destined for 10.250.16.130 is egressed via GigabitEthernet0/2 because it matches the route with the longest prefix length (/27).Answer
  2. The bracketed output [90/307200] specifies an Administrative Distance of 90 and a routing metric of 307200 for the EIGRP-learned subnet.Answer
  3. C
    A packet destined for 10.250.16.130 is routed to next-hop 192.168.1.10 because static routes possess a lower Administrative Distance than connected routes.
  4. D
    The bracketed notation [110/20] indicates an Administrative Distance of 20 and an OSPF cost metric of 110.

Answer

Packets for 10.250.16.130 match the /27 route out GigabitEthernet0/2 due to the longest prefix match rule, and the bracketed entry [90/307200] defines Administrative Distance as 90 and Metric as 307200.
When forwarding an IP packet, the router selects the route that matches the destination IP address with the longest prefix length (most specific subnet mask). Destination 10.250.16.130 fits within 10.250.16.128/27, which is a longer prefix than /26, /24, or /20, making GigabitEthernet0/2 the correct egress path. Additionally, Cisco IOS displays administrative distance and metric formatted as [Administrative Distance/Metric], meaning [90/307200] denotes an AD of 90 and a metric of 307200.

Step-by-Step Solution

1
Evaluate destination IP 10.250.16.130 against all matching prefix ranges in the routing table.
10.250.16.130 falls into 10.250.16.0/20, 10.250.16.0/24, 10.250.16.128/26, and 10.250.16.128/27.
The router determines all candidates that enclose the destination IP address.
2
Apply the Longest Prefix Match (LPM) rule to select the best forwarding path among matching routes.
The subnet 10.250.16.128/27 has the longest prefix length (/27 > /26 > /24 > /20) and is chosen, forwarding the packet out GigabitEthernet0/2.
Longest prefix match always takes precedence over administrative distance or metric when forwarding IP traffic.
3
Decode the standard Cisco IOS bracketed routing table fields [AD/Metric].
For [90/307200], 90 is the Administrative Distance (EIGRP internal default) and 307200 is the EIGRP composite metric.
In Cisco IOS output format [X/Y], the first integer represents Administrative Distance and the second integer represents the protocol metric.

Key Concept

Routing Table Interpretation and Longest Prefix Match Forwarding Logic
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Topics

Routing Table Components

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