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Difficulty: Very hardIPv4 Static Routing

A network engineer is optimizing IPv4 static routing on a Cisco IOS router connected to multiple broadcast Ethernet segments. The router currently learns internal prefix 10.10.10.0/24 via OSPFv2 (Administrative Distance 110). Which TWO statements accurately describe the forwarding and configuration behavior of static routes applied to this router? (Select two.)

  1. Configuring 'ip route 10.10.10.0 255.255.255.0 GigabitEthernet0/1 120' creates a floating static route relative to OSPF, but specifying only an Ethernet exit interface forces the router to rely on Proxy ARP from the next-hop device to resolve destination MAC addresses.Answer
  2. Traffic destined to 10.10.10.130 will be forwarded via next-hop 192.168.13.2 when both 'ip route 10.10.10.0 255.255.255.0 192.168.12.2' (AD 1) and 'ip route 10.10.10.128 255.255.255.192 192.168.13.2 130' are in the routing table, because longest prefix match evaluation precedes Administrative Distance comparison.Answer
  3. C
    The command 'ip route 10.10.10.0 255.255.255.0 192.168.12.2 90' functions as a floating static backup route that remains inactive in the routing table until the primary OSPF route (AD 110) fails.
  4. D
    Configuring a static default route with 'ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/0' on a multi-access Ethernet interface eliminates recursive routing lookups while preventing unnecessary ARP table bloat.

Answer

The correct options are the statement regarding Proxy ARP dependency when using an Ethernet exit interface for a floating static route with Administrative Distance 120, and the statement confirming that longest prefix match (/26 over /24) dictates path selection over Administrative Distance during packet forwarding.
The option describing a floating static route with AD 120 is correct because floating backup routes must have a higher AD than the primary protocol (OSPF = 110), and specifying an Ethernet interface without a next-hop IP requires Proxy ARP to discover destination MAC addresses. The option addressing destination 10.10.10.130 is also correct because the router prioritizes the most specific prefix match (/26 over /24) during forwarding lookup regardless of the AD of the installed static routes.

Step-by-Step Solution

1
Evaluate floating static route behavior and exit interface considerations.
OSPF has a default AD of 110. A static route configured with AD 120 has a higher distance, floating out of the routing table until OSPF fails. On broadcast Ethernet interfaces, omitting the next-hop IP forces ARP queries for individual target IPs, requiring Proxy ARP on adjacent devices.
Floating routes require AD > primary protocol AD. Broadcast interfaces need explicit next-hop IPs to prevent per-destination ARP lookups.
2
Analyze routing decision hierarchy (Longest Prefix Match vs Administrative Distance).
Administrative distance determines which routes are installed into the routing table. Once installed, packet forwarding decisions rely strictly on the Longest Prefix Match (/26 mask matches 10.10.10.130 more specifically than /24).
Prefix length (/26 > /24) takes absolute priority during active packet forwarding lookup.
3
Identify misconceptions in backup static route AD configuration and default route exit interface usage.
Configuring AD 90 makes the static route primary over OSPF (AD 110), failing the floating backup requirement. Pointing a static route (or default route) solely to an Ethernet exit interface causes severe ARP table expansion.
Lower AD wins installation; broadcast interfaces treat all destinations as local when no next-hop IP is provided.

Key Concept

IPv4 Static Route Selection, Administrative Distance, and Exit Interface Dynamics
Estimated Time:3m 0s
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Topics

IPv4 Static Routing

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