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Zorluk: OrtaRouting Table Components

A network administrator issues the `show ip route` command on a Cisco router and observes the following partial routing table output:

text
Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 4 subnets, 3 masks
O 10.20.0.0/16 [110/20] via 192.168.12.2, 00:15:10, GigabitEthernet0/0
D 10.20.30.0/24 [90/307200] via 192.168.23.3, 01:42:15, GigabitEthernet0/1
S 10.20.30.128/25 [1/0] via 192.168.34.4, GigabitEthernet0/2
O E2 10.0.0.0/8 [110/20] via 192.168.12.2, 00:05:22, GigabitEthernet0/0

Which TWO statements correctly describe the forwarding behavior and components of this routing table? (Select TWO.)

  1. A packet destined for 10.20.30.140 is egressed via GigabitEthernet0/2 because 10.20.30.128/25 provides the longest prefix match.Cevap
  2. B
    The route entry for 10.20.30.0/24 indicates an Administrative Distance of 307200 and a routing metric of 90.
  3. For a packet destined to 10.20.30.150, the router prefers the static route (10.20.30.128/25) over the OSPF route (10.20.0.0/16) primarily due to prefix length rather than administrative distance.Cevap
  4. D
    A packet destined for 10.20.30.50 is routed out interface GigabitEthernet0/0 because OSPF has a lower metric than EIGRP.

Cevap

The router forwards a packet destined for 10.20.30.140 out GigabitEthernet0/2 due to the longest prefix match (/25), and it evaluates prefix length prior to Administrative Distance when choosing between 10.20.30.128/25 and 10.20.0.0/16 for host 10.20.30.150.
Routing table lookups prioritize the Longest Prefix Match (most specific subnet mask). For 10.20.30.140, the /25 route matches and is more specific than /24, /16, or /8, directing traffic to GigabitEthernet0/2. Similarly, prefix specificity overrides administrative distance when comparing non-identical prefix lengths such as /25 versus /16.

Adım Adım Çözüm

1
Parse the bracketed notation [AD/Metric] for Cisco routing entries.
In [90/307200], Administrative Distance is 90 and the composite metric is 307200.
Distinguishes Administrative Distance from protocol metrics.
2
Evaluate the IP destination 10.20.30.140 against candidate routing table entries.
Matches 10.0.0.0/8, 10.20.0.0/16, 10.20.30.0/24, and 10.20.30.128/25 (valid host range 10.20.30.129–10.20.30.254).
Identifies all candidate routes containing the destination IP address.
3
Apply the Longest Prefix Match (LPM) rule.
Selects 10.20.30.128/25 over shorter prefixes (/24, /16, /8), routing out GigabitEthernet0/2.
Prefix length length determines matching priority before administrative distance is ever evaluated for unequal prefixes.

Anahtar Kavram

Routing Table Components and Longest Prefix Match Determination
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Konular

Routing Table Components

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