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Zorluk: Çok zorIPv4 Static Routing

An enterprise edge router receives internal routing updates for the prefix 192.168.50.0/24192.168.50.0/24 via OSPFv2 (Administrative Distance 110) and iBGP (Administrative Distance 200). A network administrator intends to provision a floating static route via next-hop 10.0.12.210.0.12.2 that remains inactive during normal operation, activates as a backup if the OSPF path fails, and takes precedence over the iBGP path. The administrator executes the following Cisco IOS command:

`ip route 192.168.50.0 255.255.255.0 10.0.12.2 105`

What is the operational result of this configuration, and what modification is required to achieve the desired routing behavior?

  1. The static route immediately replaces the OSPF route in the routing table because its Administrative Distance of 105 is lower than 110; the Administrative Distance must be reconfigured to a value between 111 and 199.Cevap
  2. B
    The static route is installed in the routing table alongside OSPF to perform equal-cost multipath load balancing; the distance must be set to 201 to force failover.
  3. C
    The static route remains inactive because static routes cannot override dynamic routing protocols unless the permanent keyword is appended; the command syntax must be updated.
  4. D
    The static route is rejected by Cisco IOS because Administrative Distance values below 110 are strictly reserved for internal Cisco protocols; the next-hop IP must be replaced with a exit interface.

Cevap

The static route immediately overrides the OSPF path because an Administrative Distance of 105 is lower than OSPF's default distance of 110. To function as a floating static backup for OSPF while remaining preferred over iBGP, the Administrative Distance must be configured to a value strictly between 111 and 199.
Cisco IOS selects routes for installation in the routing table based on Administrative Distance (AD), where lower values represent higher trustworthiness. OSPFv2 has a default AD of 110 and iBGP has a default AD of 200. Configuring the static route with AD 105 makes it more trustworthy than OSPF (105<110105 < 110), causing it to immediately active in the routing table rather than functioning as a backup. To properly float behind OSPF but remain ahead of iBGP, its AD must be set within the range of 111 to 199 (such as 120).

Adım Adım Çözüm

1
Analyze the Administrative Distance (AD) hierarchy of the active protocols and proposed static route.
Primary path: OSPFv2 (AD 110). Secondary requirement: Floating static backup. Tertiary path: iBGP (AD 200). Configured static route AD: 105.
Administrative Distance determines route trustworthiness in the Cisco IOS Routing Table. Lower AD values are preferred.
2
Evaluate the effect of configuring AD 105 on the router.
Since 105<110105 < 110, the static route overrides OSPF immediately and enters the routing table as the active route, breaking its intended role as a backup route.
A floating static route must have an AD higher than the primary route protocol so that it remains inactive until the primary route drops.
3
Determine the valid AD range for the floating static route.
The AD value XX must satisfy 110<X<200110 < X < 200 (e.g., X=120X = 120).
This guarantees that OSPF (110) is preferred when available, the static route (XX) activates when OSPF fails, and iBGP (200) is used only as a last resort.

Anahtar Kavram

Floating Static Route Administrative Distance Calibration
Tahmini Süre:2m 0s
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Konular

IPv4 Static Routing

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