From: Kelly Cobean (kcobean@earthlink.net)
Date: Thu Feb 13 2003 - 01:02:17 GMT-3
Correct. If I remember correctly, HDLC is a "vendor-specific" protocol
because it does not contain the "protocol" field in the header to indicate
what the upper layer protocol is, where PPP does by the RFC (1661 or 1670?).
As a result, each vendor relies on their own implementation to pass data to
the proper layer 3 process. If I remember correctly, instead of the "type"
field, HDLC includes a length field, but I could be mistaken. Hope this
helps. Below is a snippet of RFC1661 if you care to read it...
Kelly Cobean
A summary of the PPP encapsulation is shown below. The fields are
transmitted from left to right.
+----------+-------------+---------+
| Protocol | Information | Padding |
| 8/16 bits| * | * |
+----------+-------------+---------+
Protocol Field
The Protocol field is one or two octets, and its value identifies
the datagram encapsulated in the Information field of the packet.
The field is transmitted and received most significant octet
first.
The structure of this field is consistent with the ISO 3309
extension mechanism for address fields. All Protocols MUST be
odd; the least significant bit of the least significant octet MUST
equal "1". Also, all Protocols MUST be assigned such that the
least significant bit of the most significant octet equals "0".
Frames received which don't comply with these rules MUST be
treated as having an unrecognized Protocol.
Protocol field values in the "0***" to "3***" range identify the
network-layer protocol of specific packets, and values in the
"8***" to "b***" range identify packets belonging to the
associated Network Control Protocols (NCPs), if any.
Protocol field values in the "4***" to "7***" range are used for
protocols with low volume traffic which have no associated NCP.
Protocol field values in the "c***" to "f***" range identify
packets as link-layer Control Protocols (such as LCP).
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Joe
Sent: Wednesday, February 12, 2003 8:09 PM
To: 'stefan vogt'; ccielab@groupstudy.com
Subject: RE: Is Cisco HDLC encapsulation proprietary?
I think it is.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
stefan vogt
Sent: Tuesday, February 11, 2003 10:34 AM
To: ccielab@groupstudy.com
Subject: Is Cisco HDLC encapsulation proprietary?
Hi all,
I'm just trying to get a HDLC connection between a Cisco router and a
Bintec router to work. I already disabled keepalives on the Cisco side,
but it still doesn't work. Is there anything special with the Cisco HDLC
encapsulation (ie. proprietary)?
TIA,
Stefan
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