Re: SNMPv3: BER encode problem of msgMaxSize

Sun, 03 Feb 2008 13:16:19 -0800

Attachment: v3-maxsize-3.pcap
Description: Binary data


Attach is a pcap file which recorded this communication progress.

First 4 packet is a SNMPv3/authPriv/GET PDU, I use 3-bytes msgMaxSize to get sysDescr.0's value and succeed.

The fifth packet is a another talk to SNMPd, the packet is just a SNMPv3 get-request to get a report, with 2-bytes msgMaxSize, but I never got a response from SNMPd.

Thanks,

Chun TIAN (binghe)

On Feb 4, 2008, at 4:59 AM, Chun Tian (binghe) wrote:

Hi, Net-SNMP developers

It seems that Net-SNMP has a fixed msgMaxSize in SNMPv3 message, which is 65507. I found this value is BER-encoded to:

0x02 (type: integer), 0x03 (length: 3), 0x00, 0xff, 0xe3 (0xffe3 = 65507)

What I don't know is why this value must be encoded to a 3-bytes integer, not 2-bytes, just like this:

0x02, 0x02, 0xff, 0xe3

I'm writing a pure Common Lisp SNMP client package [1], when I encode msgMaxSize to 3 bytes, as Net-SNMP's own client does, it's all right; When I encode msgMaxSize to 2 bytes, SNMPd will not response.

Why?

Chun TIAN (binghe)
NetEase.com, Inc.



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