In addition to Paul's very relevant comments, I have recently worked
through a problem with PPP multilink (i.e. it doesn't work) when used in
conjunction with priority queueing with various 12.0 IOS versions, I think
including 12.0(8). This was on an AS5300, though, not a 2500.
I don't believe the TAC ever gave it a bug number, despite some prompting,
but an upgrade to 12.1(4) fixed the problem.
If IBM thinks they do support multilink, try stripping your Cisco config of
every non-essential item, even if it doesn't seem to be related to PPP.
debug ppp negotiation and debug ppp packet were quite useful in my case in
tracking down the problem, including seeing if the MRRU LCP option is
requested or rejected. There are various other debug ppp options available
which may be useful.
JMcL
---------------------- Forwarded by Jenny Mcleod/NSO/CSDA on 04/01/2001
04:44 pm ---------------------------
Paul Werner <[EMAIL PROTECTED]>@groupstudy.com on 04/01/2001 03:41:44 pm
Please respond to Paul Werner <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED]
To: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]>
cc:
Subject: Re: Subject: Multilink PPP with ISDN between Cisco 2504 and IBM
2210
A couple of thoughts. First, can I presume from your statement
below that you are able to initiate a call from the Cisco router
to the IBM 2210 (even if it is not multilink). According to
IBM's web site, the 2210 does support PPP multilink.
Nevertheless, like Animal Farm's pigs, some support for
multilink may be more equal than others. I note on IBM's web
page that there is not an explicit support for the RFCs that
cover PPP (unlike Cisco's support). This may indicate
compatability problems.
http://www.networking.ibm.com/220/220over.html#s20
I think you have hit upon a key ingredient for
interoperability, namely the negotiated maximum received
reconstructed unit (MRRU). To quote from RFC 1990, here is
paragraph 5.1.1 (excerpt):
The Max-Receive-Reconstructed unit field is two octets, and
specifies the maximum number of octets in the Information
fields of reassembled packets. A system MUST be able to
receive the full 1500 octet Information field of any
reassembled PPP packet although it MAY attempt to negotiate a
smaller, or larger value. The number 1500 here comes from the
specification for the MRU LCP option in PPP; if this
requirement is changed in a future version of RFC1661 the same
rules will apply here.
I think one key to minimizing the headache here will be to go
to that MRRU which both hosts must be able to support. If you
leave most of your interfaces at their default, a 1500 MRRU
should be attainable. While looking to see what configurations
commands might affect the MRRU, I noticed that it *appears* the
2210 does not have explicit support for PPP multilink, nor does
it *appear* to have an LCP option to negotiate it. I hope I
read the IBM configuration guide incorrectly. See chapter 28
(watch wrap):
http://publib.boulder.ibm.com/cgi-
bin/bookmgr/BOOKS/E2FB5004/CCONTENTS
Additionally, this passage from IBM's marketing brochure did
not inspire confidence that standards based (RFC 1990)
multilink was used in the 2210:
http://www.networking.ibm.com/220/220over.html
Specifically,
"Hardware and software for dependable routing solutions
When equipped with one of the many available ISDN adapters, the
2210 Nways Multiprotocol Router and Nways MRS are dependable
ISDN solutions. The Quad BRI adapter offers increased bandwidth
and provides backup capability without requiring more expensive
Primary Rate ISDN (PRI) service. With the Point-to-Point
Protocol multilink tool?supplied with the 2210?bandwidth can be
increased dynamically by grouping the B-channels. And for even
greater bandwidth administration, rely on IBM's award-winning
Bandwidth Reservation System (BRS) to manage traffic priority
over Frame Relay, PPP and dial connections.
I have never heard of multilink referred to as a "tool".
HTH,
Paul Werner
> Subject: Multilink PPP with ISDN between Cisco 2504 and IBM
2210 [Virus
> checked]
>
> Hello all,
>
> we must install Cisco Router in our IBM environment :)) . We
solved a =
> lot
> of problems but we have one unsolved problem:
>
> The Cisco router must dialed-in to the IBM router with both
ISDN B
> channels. The connection comes not up with the feature
multilink. We te=
> sted
> a lot of possibilties:
>
> - - dial-in Cisco <-> Cisco with and without Multilink is o.k.
> - - dial-in IBM <-> IBM with and without Multilink is o.k.
> - - dial-in Cisco <-> IBM without Multilink (one ISDN B
channel) is also
> =
> o.k.
>
> Only the multilink solution between Cisco an IBM doesn=B4t
work.
>
> Have any of you an idea ??
> We think that we have a problem with the LCP layer. For
instance how ca=
> n I
> set the MRRU ?
>
> Software: c2500-is-l_120-8.bin and eptf09i.e11
>
> See the files (configuration of the Cisco router and a debug
of the IBM=
> ),
> please.
>
> (See attached file: Multilink.log)(See attached file:
cisco2504.log)
>
> Thank=B4s a lot.
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