Date: Sat, 2 Dec 2000 09:41:11 +0100 (CET) From: hm@kts.org (Hellmuth Michaelis) To: i4b@zabbadoz.net (Bjoern A. Zeeb) Cc: hm@hcs.de, freebsd-isdn@FreeBSD.ORG Subject: Re: cisco hdlc [was: i4bing -> panic] Message-ID: <20001202084111.ECED69B1C@bert.kts.org> In-Reply-To: <Pine.BSF.4.30.0012012225550.73161-100000@noc.zabbadoz.net> from "Bjoern A. Zeeb" at "Dec 1, 2000 11:23:16 pm"
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Bjoern A. Zeeb wrote:
> --- snipp ---
> HDLC is used for the IP over ISDN interfaces ipr and isp. In case of
> the ipr driver, IP frames are put directly into those HDLC frames and
> sent to the remote site; in the case of isp IP frames are encapsulated
> into PPP frames which in turn are put into the HDLC frames.
> --- snipp ---
ipr driver:
+------------+--------------------------------------+----------+-----------+
| HDLC flag | IP - packet | HDLC CRC | HDLC flag |
+------------+--------------------------------------+----------+-----------+
isp and userland ppp:
+------------+--------------------------------------+----------+-----------+
| HDLC flag | PPP frame (see below) | HDLC CRC | HDLC flag |
+------------+--------------------------------------+----------+-----------+
| PPP head | IP - packet | PPP trailer |
+--------------------------------------+
> ok. now there are two types of keepalives:
> 1. cisco hdlc slarp keepalives
> 2. "ppp keepalives"
> that have nothing in common that the part of the name (highly
> simplified).
Correct.
AFAIK, Cisco HDLC is more like the ipr way of doing things with the addition
of adding a second encapsulation providing a "packet" type to distinguish
between control packets (i.e. keepalives) and data packets (payload data).
> So why is cisco hdlc implemented in isp instead of ipr if it is only
> using "raw hdlc" with slarp extetions ?
I don't know. It is part of the sppp subroutine set. Was it perhaps phk who
added this (Poul-Henning, are you listening ?).
> So what I would have to use is ipr with slarp extentions.
This would be a natural way if it was not there, but i think it is already
there in the isp/isppp interface, so why do doubled work ?
hellmuth
--
Hellmuth Michaelis hm@kts.org Hamburg, Europe
We all live in a yellow subroutine, yellow subroutine, yellow subroutine ...
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