[lwip-users] Incorrect RequestID field in SNMP response message

[Lubomir Toshev]

Hello,

I have ported lwIP 1.2.0 to a proprietary Coldfire system. I do not
use RTOS and I work with a single thread. I use UDP communication as
well as the SNMP agent. UDP communication works fine, but I have some
problems with the SNMP agent.

I noticed a mismatch between the RequestID fields of the request and
response messages in an SNMP communication sequence. Some SNMP
managers (like HostMonitor) succeed to GET values despite this
mismatch. Others however (like Net-SNMP) will reject the response.

It seems the RequetID field generated by my system has reversed byte
order. Other fields of the message are encoded correctly, for example
the specific variable values (sysUpTime, etc.).

I am not sure if this is an issue of lwIP or it is related to my port.
Please, make some comments on the possible reasons. What shall I be
more carefull about?

Two examples of SNMP GET request/response are given below. The first
one is between HostMomitor (manager) and lwIP (agent). The second one
is between Net-SNMP (manager) and lwIP (agent). Network traffic is
captured by WireShark.

1. HostMonitor <-> lwIP (HostMonitor accepts the response)

SNMP GET requet:
RequestID is encoded 02 01 01 which is interpreted as "1"

SNMP GET response:
RequestID is encoded 02 04 01 00 00 00 which is interpreted as "16777216"

SysUpTime value is encoded 43 03 00 9d c7 which is correct

These are the two messages:
+---------+---------------+----------+
04:39:39,029,776   ETHER
|0   
|00|06|70|00|00|01|00|c0|9f|16|ba|a3|08|00|45|00|00|44|00|a9|00|00|80|11|b8|
aa|c0|a8|00|02|c0|a8|00|03|0b|e5|00|a1|00|30|3b|79|30|26|02|01|00|04|06|70|75|62|
6c|69|63|a0|19|02|01|01|02|01|00|02|01|00|30|0e|30|0c|06|08|2b|06|01|02|01|01|03|
00|05|00|

+---------+---------------+----------+
04:39:39,030,235   ETHER
|0   
|00|c0|9f|16|ba|a3|00|06|70|00|00|01|08|00|45|00|00|4a|00|11|40|00|ff|11|fa|
3b|c0|a8|00|03|c0|a8|00|02|00|a1|0b|e5|00|36|fa|ef|30|2c|02|01|00|04|06|70|75|62|
6c|69|63|a2|1f|02|04|01|00|00|00|02|01|00|02|01|00|30|11|30|0f|06|08|2b|06|01|02|
01|01|03|00|43|03|00|9d|c7|

2. Net-SNMP <-> lwIP (Net-SNMP rejects the response)

SNMP GET requet:
RequestID is encoded 02 02 70 06 which is interpreted as "28678"

SNMP GET response:
RequestID is encoded 02 04 06 00 00 00 which is interpreted as "100663296"

SysUpTime value is encoded 43 03 01 0F 57 which is correct

These are the two messages:
+---------+---------------+----------+
04:44:59,264,042   ETHER
|0   
|00|06|70|00|00|01|00|c0|9f|16|ba|a3|08|00|45|00|00|45|00|ae|00|00|80|11|b8|
a4|c0|a8|00|02|c0|a8|00|03|0b|e6|00|a1|00|31|a2|96|30|27|02|01|00|04|06|70|75|62|
6c|69|63|a0|1a|02|02|70|06|02|01|00|02|01|00|30|0e|30|0c|06|08|2b|06|01|02|01|01|
03|00|05|00|

+---------+---------------+----------+
04:44:59,264,466   ETHER
|0   
|00|c0|9f|16|ba|a3|00|06|70|00|00|01|08|00|45|00|00|4a|00|12|40|00|ff|11|fa|
3a|c0|a8|00|03|c0|a8|00|02|00|a1|0b|e6|00|36|89|59|30|2c|02|01|00|04|06|70|75|62|
6c|69|63|a2|1f|02|04|06|00|00|00|02|01|00|02|01|00|30|11|30|0f|06|08|2b|06|01|02|
01|01|03|00|43|03|01|0f|57|


-- 
Best regards,
 Lubo