Cisco Cisco IOS Software Release 12.2(15)B

Enter the show running-config interface command. The following display shows ACFC being enabled 
on a synchronous serial interface:

Router# show running-config interface serial1/3

Building configuration...

Current configuration :303 bytes

!

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interface Serial1/3

encapsulation ppp

ppp acfc local request      <----

ppp acfc remote apply       <----

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Enter the debug ppp negotiation command. The following displays ACFC enabled:

%LINK-3-UPDOWN:Interface Serial1/3, changed state to up

    Se1/3 PPP:Using default call direction

    Se1/3 PPP:Treating connection as a dedicated line

    Se1/3 PPP:Phase is ESTABLISHING, Active Open [0 sess, 1 load]

    Se1/3 LCP:O CONFREQ [Closed] id 4 len 12

    Se1/3 LCP:   MagicNumber 0x3025FBB3 (0x05063025FBB3)

    Se1/3 LCP:   ACFC (0x0802) ! The local router requests the ACFC option

    Se1/3 LCP:I CONFREQ [REQsent] id 7 len 12

    Se1/3 LCP:   MagicNumber 0x3026B1FC (0x05063026B1FC)

    Se1/3 LCP:   ACFC (0x0802) ! The romote peer requests the ACFC option

Router(config-if)# ppp pfc local {request 

| forbid}

Configures how the router handles PFC in its outbound 
configuration requests.

request—The PFC option is included in outbound 
configuration requests.

forbid—The PFC option is not sent in outbound 
configuration requests, and requests from a remote peer to 
add the PFC option are not accepted.

Router(config-if)# no shutdown

Reenables the interface.