What is enabled by default on Cisco IOS-XR routers and cannot be disabled?

The correct answer is C. IPv4 and IPv6 CEF. On Cisco IOS-XR, IPv4 and IPv6 Cisco Express Forwarding (CEF) is always enabled and cannot be disabled. CEF is the fundamental hardware-accelerated forwarding mechanism in IOS-XR's architecture - it builds the Forwarding Information Base (FIB) from the Routing Information Base…

Unicast Routing

Question

Options

ASSH server
BMulticast routing
CIPv4 and IPv6 CEF
DIPv6 routing
ECDP
FBFD

How the community answered

(21 responses)

C
86% (18)
E
5% (1)
F
10% (2)

Explanation

On Cisco IOS-XR, IPv4 and IPv6 Cisco Express Forwarding (CEF) is always enabled and cannot be disabled. CEF is the fundamental hardware-accelerated forwarding mechanism in IOS-XR's architecture - it builds the Forwarding Information Base (FIB) from the Routing Information Base (RIB) and is integral to how the platform processes packets. Unlike classic IOS where 'no ip cef' was a valid command, IOS-XR does not provide any mechanism to disable CEF. SSH server (A) must be explicitly configured. Multicast routing (B) is disabled by default. IPv6 routing (D) and CDP (E) are configurable. BFD (F) requires explicit configuration per interface.

Topics

#IOS-XR#CEF#Forwarding Plane#Default Behavior

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