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Conference azur::mcc

Title:	DECmcc user notes file. Does not replace IPMT.
Notice:	Use IPMT for problems. Newsletter location in note 6187
Moderator:	TAEC::BEROUD

Created:	Mon Aug 21 1989
Last Modified:	Wed Jun 04 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	6497
Total number of notes:	27359

4457.0. "DECmcc v1.3 and Network General's Sniffer problems" by MUTTON::LAMB (Peter Lamb - GSG Santa Clara) Tue Jan 26 1993 21:53

    Hello,
    
    I just sopke to Aerospace Corporation (a 1.3 field test site)
    and they are having difficulty getting SNMP requests to work
    with the Network General Sniffer.
    
    They don not have any problems talking to the sniffer from either 
    the HP or Sun network management products but something about the
    way we talk to it seems to be causing problems.  They have done
    a fairly exhaustive investigation of this and believe that it may be
    related to one of two things that DECmcc seems to be doing differently
    (then the other packages).
    
    (please excuse my ignorance on some of this I am relaying the
    information to the best of my ability)
    
    1) A typical SNMP query contains a tag, length and value fields
    according to Aerospace DECmcc is expanding the length field to 3 
    bytes (which should be ok according to the standard) but none of the
    other packages are doing this so the suspicion is that this may be 
    causing the network general problems.
    
    2) With DECmcc a request id is always a 1 (one) all of the other
    packages seem to be using much larger numbers.
    
    Note:  by not working what I mean is that any attempt to do say a
    show characteristics of the sniffer at even the top most level
    just fails.
    
    I guess that is all I can think of now.
    
    Hopefully I have provided enough information to give some clue as to
    what might be the problem - frankly, I was supprised when I searched
    through the conference that problems talking to the network sniffer 
    had not been discussed previously.
    
    Regards,
    
    Peter Lamb

T.R	Title	User	Personal Name	Date	Lines
4457.1		MOLAR::YAHEY::BOSE		`Thu Jan 28 1993 09:26`	22
	The DECmcc SNMP AM uses standard ASN.1 basic encoding rules (BER) and the structure of the PDU sent out by the AM should not differ in any way from what HP or SUN are sending out. In fact, we have been shipping the SNMP AM for 2 1/2 years and never have we heard any complaints regarding the PDU structures (and that layer of code has not changed since V1.0). The only difference I can think of between HP/SUN and DECmcc is that we mainly use the SNMP Get request while they use the GetNext request. The question is does the sniffer implement Get responses properly? Use the mib query utility to walk through the mib objects using the GetNext operation. (You could also do a GetNext operation from DECmcc by doing a wildcarded show on a table entity, like the interface table). Another thing you might want to check is whether the DECmcc management station has read access on the agent. This is a common problem faced by people setting up SNMP management stations. Rahul.
4457.2	Customer's reply	DAGWST::LAMB	Peter Lamb - GSG Santa Clara	`Fri Jan 29 1993 10:09`	17
	Hello, I spoke to the customer about your reply and here is their response I agree that BER rules are being followed. What I noticed is that the Length field is expanded. For instance the encoding of - tag,length,value - sequence of ...with 12 bytes should be 30 0C. DECmcc expands this into 30 82 00 0C. Legal BER but unnecessary (maybe the Sniffer agent can't handle this?). We utilized some code from CMU to send a SNMP Get Request from the DEC station to the Sniffer and that works OK (non-expanded length field). The only other difference between these two messages is CMU's packet has Request ID 77827118 (large arbitrary number) and DECmcc always uses a Request ID of 1. DECmcc 1.3 does not even recognize the sniffer agent...it will not let us add the MIB icon to the list of SNMP objects for the Sniffer. MIB walk does not work. Community string (access to the agent) is not a problem.
4457.3		MOLAR::YAHEY::BOSE		`Fri Jan 29 1993 13:21`	18
	Peter, I understand with the current ASN.1 encodings you may not be able to query the Sniffer agent from DECmcc. Trying to change the ASN.1 encodings at this juncture is going to be an extremely risky proposition. It may also mean changes to the DECmcc kernel, since the SNMP AM uses the ASN.1 kernel routines. I would suggest that the customer talk with Network General explaining the problem, since it may not be too difficult a task removing the current limitation from the agent software. This problem is going to be a temporary one since for our SNMP V2 implementation we intend to start using Jeff Case's code base for the low level protocol engine. We expect that all agents will standardise around this code, thereby removing any possibility of the sort of problems your customers are facing now. Rahul.