What does the ECN value 01/10 signify?

What does the ECN value 01/10 signify?

• A. Not Protocol aware or negotiating
• B. 01/10: Both endpoints are protocol aware
• C. Congestion experienced and marked by router
• D. Reserved for future use

Answer: (B)

ECN uses two bits in the IP header to indicate whether endpoints support ECN and to signal congestion. The two-bit field has defined codepoints: 00 means not ECN-capable, 01 and 10 indicate ECN-capable (ECT) endpoints, and 11 means congestion has been experienced (CE). When you see 01 or 10, it shows that both ends of the communication are ECN-capable, so ECN can be used for congestion signaling (routers may mark CE without dropping packets). That’s why this option—the indication that both endpoints are protocol aware—best fits the meaning of 01/10. The other codepoints correspond to different states: 00 is not ECN-capable, 11 is congestion experienced, and “reserved for future use” does not apply here.

ECN uses two bits in the IP header to indicate whether endpoints support ECN and to signal congestion. The two-bit field has defined codepoints: 00 means not ECN-capable, 01 and 10 indicate ECN-capable (ECT) endpoints, and 11 means congestion has been experienced (CE). When you see 01 or 10, it shows that both ends of the communication are ECN-capable, so ECN can be used for congestion signaling (routers may mark CE without dropping packets). That’s why this option—the indication that both endpoints are protocol aware—best fits the meaning of 01/10. The other codepoints correspond to different states: 00 is not ECN-capable, 11 is congestion experienced, and “reserved for future use” does not apply here.