HDLC vs PPP

[moses12315]

I have 50 routers(Cisco) connected with leased lines. Which protocol shall i use HDLC or PPP. Does PPP offers me more about security or leave the default of Cisco .

[Amit Singh]

PPP was and is heavily used in async dial-up and provide for authentication using PAP or CHAP protocol. Now there is also PPP over

Ethernet (PPPoE).

A variation of PPP known as multi-link PPP (MLPPP) is quite popular for loading balancing parallet circuit like T1's.MLPPP also provides the frame interleaving and fragmentation on the interface.

Cisco's implementation of HDLC is proprietary. It has an extra field in the frame that allows it to define the layer 3 protocol(s) that's encapsulated in it. normal HDLC doesn't have this field.

Cisco's HDLC will operate with "devices that can interpret the Cisco HDLC frame type." So, i guess if another vendor's routers support Cisco HDLC, then it's possible to use it. otherwise, as Layer3 says, PPP is best for "non-Cisco devices".

HDLC is used on point-to-pont serial links suc as T1s, DS3 and now Packet-over-SONET (POS). It has a low overhead in terms of the additional bytes required over and above the layer 3 payload. There is no authentication protocol for HDLC.

HTH,Please rate if it does.

-amit singh

[Richard Burts]

Moses

PPP does have the option to do authentication (with PAP or CHAP) which HDLC does not. Given that the connections are leased lines, I do not see any reason to do authentication. In which case I do not see any particular advantage to using PPP and I would advise you to use the default of HDLC.

HTH

Rick

[mohammedmahmoud]

Hi,

Totally agree with Rick, unless needing PPP features like authentication, compression and MLPPP, thus using HDLC (default / less overhead) would make more sense.

HTH,

Mohammed Mahmoud.