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Community Member

Practical advantages:encapsulation HDLC vs PPP

Folks, is there any reason one should be using HDLC as layer 2 encapsulation these days?

I know that PPP provides authentication and information I have is that when it comes to overhead, they are very similar.

In case you see practical reasons or advantages of using HDLC please let me know.

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Hall of Fame Super Silver

Re: Practical advantages:encapsulation HDLC vs PPP

Hello Marlon,

I agree also PPP provides for loopback detection with the PPP magic number, link quality monitor and it is standards based.

only disadvantage:

you need to add encapsulation ppp in interface configuration

Hope to help

Giuseppe

8 REPLIES
Hall of Fame Super Silver

Re: Practical advantages:encapsulation HDLC vs PPP

Hello Marlon,

I agree also PPP provides for loopback detection with the PPP magic number, link quality monitor and it is standards based.

only disadvantage:

you need to add encapsulation ppp in interface configuration

Hope to help

Giuseppe

Community Member

Re: Practical advantages:encapsulation HDLC vs PPP

Great.


One more point:
HDLC  was developed by Cisco and therefore it is proprietary, right?

So I would pick PPP if using open standard (in case other router brand is ever introduced) is to be considered.

Re: Practical advantages:encapsulation HDLC vs PPP

Good post

Community Member

Re: Practical advantages:encapsulation HDLC vs PPP

Thanks for all good answers.

Just a correction on my own assumption:Juniper does support HDLC as well.

Cisco Employee

Re: Practical advantages:encapsulation HDLC vs PPP

Marlon,

The HDLC is a standard and many vendors should support it. The question is whether they also support the slightly changed Cisco version of the HDLC. The original HDLC did not have a protocol ID field so an HDLC circuit could transport only a single protocol. Cisco improved this limitation at the expense of making its own cHDLC incompatible with the standard. Actually, the "HDLC" run by default on Cisco serial and ISDN interfaces is the cHDLC, not the plain basic HDLC.

You may find more details here:

http://en.wikipedia.org/wiki/Cisco_HDLC

Best regards,

Peter

Hall of Fame Super Silver

Re: Practical advantages:encapsulation HDLC vs PPP

Hello Marlon,

Juniper supports also Cisco HDLC

Peter is right about what makes the difference between Cisco HDLC and original HDLC

Hope to help

Giuseppe

Cisco Employee

Re: Practical advantages:encapsulation HDLC vs PPP

Marlon, Giuseppe,

I completely agree with Giuseppe, adding features like support for compression (though Cisco HDLC supports it, too), multilink PPP with optional LFI mechanism, extensible authentication and probably others.

An irony is that the PPP datagrams themselves are encapsulated in HDLC-like framing RFC 1662 describes the gory details.

Best regards

Peter

Community Member

Re: Practical advantages:encapsulation HDLC vs PPP

I prefer to use ppp, this is very common in the industry, I work in a ISP, and everything is PPP I didn't see HDLC.

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