When a Cisco IOS Router receives a TCP packet with a TTL value less than or equal to 1, what will it do?
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A. B. C. D.C.
When a Cisco IOS Router receives a TCP packet with a TTL (Time to Live) value less than or equal to 1, it will drop the packet and reply with an ICMP (Internet Control Message Protocol) Type 11, Code 0 (Time Exceeded, Hop Count Exceeded) message.
The TTL value in a TCP packet is used to limit the lifetime of the packet and prevent it from being forwarded indefinitely in a routing loop. The TTL value is decremented by 1 by each router that forwards the packet. When the TTL value reaches 0, the packet is discarded by the router that receives it, and an ICMP error message is sent back to the source host.
In the case of a TCP packet with a TTL value less than or equal to 1, the packet has already expired and cannot be forwarded further. Therefore, the router drops the packet and sends an ICMP Type 11, Code 0 message back to the source host. This message indicates that the packet has exceeded the maximum number of hops allowed, and it provides information about the router that discarded the packet.
Option A is incorrect because the router cannot route the packet normally when the TTL value is less than or equal to 1.
Option B is incorrect because an ICMP Type 3, Code 1 message is sent when the destination host is unreachable, not when the packet TTL value is expired.
Option D is incorrect because an ICMP Type 14, Code 0 message is sent in response to a Timestamp Request message, not to a TCP packet with an expired TTL value.