[Replies redirected to cisco-nsp, where this is slightly more on-topic] * ssprunk@cisco.com (Stephen Sprunk) [Fri 22 Feb 2002, 18:49 CET]:
In practice, HDLC is the dominant encapsulation, primarily since it's Cisco's default. If for no other reason, you should use HDLC because almost everyone expects you to be using it. PPP is obviously present in non-Cisco shops, and anywhere MLPPP or LFI is needed. FR is only used as a p-t-p encapsulation in certain cases that require it; almost nobody uses it without a good reason.
Also, PPP supports authentication and you have to be careful with specifying that it's not needed for serial links towards customers, otherwise you suddenly find yourself or your customer locked out; with HDLC the risks of this are lower. Of course, you only run into this sort of trouble if your provisioning system isn't too well-thought-out, IMNSHO, or if you decide to move from basic plain password authentication to something TACACS+-based... Regards, -- Niels.