[c-nsp] Cisco HDLC Link Establishment

[Khawaja, Kashif]

I was wondering if someone could point me to the a relatively detailed
documentation on Cisco HDLC encapsulation than what I found in RFC 1547
(4.3.1 Cisco Systems point-to-point protocols). I am trying to find the
exact link negotiation mechanism that is used by this HDLC
implementation. Obviously, I was able to find this information on PPP in
its RFC but similar information on HDLC as successfully eluded me so
far.

I have the following situation where I am blocking traffic at layer 1
from RouterB --to-- RouterA at a Cisco layer 1 device. With PPP the link
does not establish at all (which is good for me). Looking at Router B,
with HDLC the link comes up (like it always does initially with Cisco
hdlc) but once it recognizes that the other side is not receiving its
keepalives i.e. it does not see an ack of its myseq, as shown by the
mineseen counter, it drops the layer 2 link. I am sure you guys can
imagine how that can create routing problems in many situations. 

Router  ----------------[Cisco Layer 1 box]--------------> Router
A                                          <--------------   B 

So, I was just curious to know what process does a link using Cisco hdlc
encapsulation goes through when establishing a connection.

Thanks.
-Kashif.