[ltp] ibmtr_cs 2.2.18 and DHCP

[Burt Silverman]

Friedemann Baitinger asks:

>How can we determine whether our RPS is screwed up? What should be done
>if it turns out be indeed screwed? Please provide a list of what to
>check where such that our network technicians can understand what to do.

I was hoping that you would not ask!

I had an old trustworthy Network General sniffer at my disposal. You can
set up the sniffer to trace all packets coming from your MAC address and
set up the sniffer for bidirectional (from and to your MAC). The sniffer
will tell you the nature of the packets, so you will know for certain which
ones are to/from the RPS. You want to look at the Frame Control byte (FC)
of the packets returned. It is the second byte in the packet, just before
the 6 byte DA and right after the Access Control byte.

You probably will see several attempts by the adapter to request the
parameters (if it does not open the first time), and a reply to each
request. If the FC in every reply is 0, then you have a bad RPS. If some
replies have 0 and some 1, this is OK; there is one adapter on the market
that has a problem with receiving a FC==1, so that is why both values would
be sent.

If you don't have a sniffer, I am fond of the iptrace utility on AIX, and
it will do essentially the same thing. I would like to see something like
it on Linux -- it probably exists and I haven't learned about it. tcpdump
is either unusable for this, or at the least it is more difficult. If you
use any of these things, maybe to be certain you are looking at the RPS
packets, well, The RPS has a MAC/functional address of C0'00'00'00'00'02.
There are not a large number of packets associated with the Open, so it
shouldn't be too difficult.

When you discover that the RPS is troublesome, I am told that it is usually
a matter of upgrading the software in the RPS (presumably, that means the
Bridge) to a newer release. So the alternative is to find out what bridge
you have, what software it is running, and what level is needed.

A bit of a nuisance, but it is certainly worth the trouble. Hope you can
make time for it.

By the way, single ring networks with no bridges do not need to have an
RPS. Part of the protocol lets the adapter know whether it should be
looking for an RPS response or not. A network operations woman who appeared
to be very knowledgable told me that there was no RPS on my lab network.
WRONG!

Regards,

Burt

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