Re: OID length

Hello,

Le 22/01/2015 10:20, Chitrang Srivastava a écrit :
> 
> I am new to SNMP world, and trying to set(SNMPv2c) an OID , which is of
> type *DisplayString*,
> 
> If string is huge like 1300 bytes or so , I see length in OID is encoded as
> 1296 (0x0510)
> 
> Byte stream I see on wire shark is like *0x04 0x82 0x05 0x10*
> 
> Why is that ? Is this SNMP v2c limitation or something ASN.1 related?

I thing the answer is here :
<http://en.wikipedia.org/wiki/X.690#The_definite_form>.

<cit.>
In contrast to the short form, the long form length octets consist of an
initial octet and one or more subsequent octets. According to the X.690
standard [] the initial length octet shall be encoded as follows:

    bit 8 shall be one;
    bits 7 to 1 shall encode the number of subsequent octets in the
length octets, as an unsigned binary integer with bit 7 as the most
significant bit;
    the value 11111111 shall not be used.
</cit.>

After the 0x04 for OCTET STRING, you have 0x82 i.e. binary 10000010.
The bit 8 is one, the bits 7 to 1 have value 2, i.e. two octets for
the actual length.

<cit.>
All bits of the subsequent octets form the encoding of an unsigned
binary integer equal to the number of octets in the contents octets.
</cit.>

0x05 0x10, then 0x0510, i.e. 1296 decimal.

Regards,
-- 
Olivier Miakinen

------------------------------------------------------------------------------
New Year. New Location. New Benefits. New Data Center in Ashburn, VA.
GigeNET is offering a free month of service with a new server in Ashburn.
Choose from 2 high performing configs, both with 100TB of bandwidth.
Higher redundancy.Lower latency.Increased capacity.Completely compliant.
http://p.sf.net/sfu/gigenet
_______________________________________________
Net-snmp-users mailing list
[email protected]
Please see the following page to unsubscribe or change other options:
https://lists.sourceforge.net/lists/listinfo/net-snmp-users