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F5 Networks F5CAB5 Exam - Topic 1 Question 8 Discussion

Posted by Jerry on Apr 04, 2026 at 12:38 PM

A BIG-IP Administrator configured the following virtual server to pass traffic on all addresses and ports. After configuration is completed, the BIG-IP Administrator notices that the virtual server is unable to pass traffic.

Plaintext

ltm virtual forwarding_any_vs {

destination 0.0.0.0:any

ip-forward

mask 255.255.255.255

profiles {

fastL4 {}

}

serverssl-use-sni disabled

source 0.0.0.0/0

translate-address disabled

translate-port disabled

}

Which part of the configuration is the cause of the issue?

Suggested Answer: B

The failure of the Forwarding (IP) virtual server is caused by an incorrect Network Mask configuration for a wildcard destination.

Wildcard Destination: The administrator intends to create a 'Wildcard' Virtual Server that listens for any destination IP address (0.0.0.0).

The Mask Conflict: A mask of 255.255.255.255 (or /32) tells the BIG-IP to look for a specific, single host address. When combined with 0.0.0.0, the system is literally looking for traffic destined for the IP 0.0.0.0, which is not a valid routable destination for standard traffic.

Correct Configuration: To allow the virtual server to catch traffic for any IP address, the mask must be changed to 0.0.0.0 (or /0). This signifies that the system should ignore all bits of the destination address and match everything.

Forwarding Logic: The rest of the configuration---including ip-forward (Forwarding IP type), translate-address disabled, and translate-port disabled---is correct for a BIG-IP acting as a router/gateway.


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18 comments · newest first
MA
Ma 2 months ago
Right, clarity is key in these questions.
AN
Anastacia 2 months ago
Let's hope the exam doesn't trick us with A.
CE
Cecily 2 months ago
Overall, B is the most likely cause.
MA
Ma 3 months ago
I still feel A could cause issues in some scenarios.
AN
Anastacia 3 months ago
Yeah, B is definitely the main problem.
CE
Cecily 3 months ago
True, but the mask seems more critical here.
MA
Ma 3 months ago
But what about A? Incorrect translate-address could be an issue too.
AN
Anastacia 3 months ago
I agree, B makes sense. It limits traffic.
CE
Cecily 3 months ago
I think it's B. The mask is too restrictive.
LA
Lawrence 4 months ago
I’m not so sure, could it be something else entirely?
BI
Billy 4 months ago
I agree, the translate-address settings look okay.
VO
Von 4 months ago
Wait, is it really just the mask causing this?
DO
Donette 6 months ago
I think the destination is fine, but the mask is off.
GE
Gearldine 6 months ago
The mask 255.255.255.255 is definitely a problem.
ST
Stephanie 6 months ago
The mask seems off to me; I feel like a more standard subnet mask would allow traffic better.
SH
Shawna 7 months ago
I practiced a similar question where the translate-address setting caused issues, but I don't recall if that's the case here.
OL
Olive 7 months ago
I think the destination being set to 0.0.0.0:any is correct for a catch-all, but I'm not sure if it conflicts with the mask.
WI
Willard 7 months ago
I remember that using a mask of 255.255.255.255 means it's a host route, which might be too restrictive for passing traffic.
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