STP designated port value of "@4" retrieved via SNMP

[David Brousseau]

Hello,

I have a ProCurve J4903A connected to a ProCurve J4903A and I am managing them with an SNMP tool.

When querying the designated port, I'm getting a value of @4 and need to understand how to interpret this value in order to map it to the connected switch's port. I understand how to interpret the other designated port values, but this one is a mystery to me.

Thanks,
--Dave

[Mohieddin Kharnoub]

Hi David

Whats the SNMP tool you are using ?

[Mohieddin Kharnoub]

Hi David

Whats the SNMP tool you are using ?

Whats the firmware of the 2800 switches ?

[David Brousseau]

From the sysDescriptor: ProCurve J4903A Switch 2824, revision I.08.105, ROM I.08.07

I have verified that the value of "@4" is returned both via Getif (MIB browser) as well as a simple snmpget (net-snmp).

I should add that I do not have telnet access to these devices, only SNMP access.

[Matt Hobbs]

Off the top of my head, I think the @ sign designates which VLAN the port belongs to.

[Matt Hobbs]

By the way, which OID are you getting?

[bergonz · Accepted solution]

If you are reading 1.3.6.1.2.1.17.2.15.1.9, then you should take into account the fact that it returns two bytes, one being the port number and the other being the port priority. You can read the bridge mib for a complete description of this value.

It seems to me that you are seeing port 4 with a priority of 0x40.

If you are using net-snmp you should use -Ox in order to display output as Hex even when retrieving a possible string.

Regards,
Bergonz

[David Brousseau]

Bergonz, you are correct, that is the OID that I am retrieving.

From the same device, I get the following via net-snmp:

dot1dStpPortDesignatedPort.45 = Hex-STRING: 00 2D
dot1dStpPortDesignatedPort.46 = Hex-STRING: 80 01
dot1dStpPortDesignatedPort.52 = STRING: "@4"

You bring up a valid point about the formatting of the output. net-snmp may be converting "0x4034" to the string "@4" at instance 52 because there is a hex-to-ascii printable conversion for both octets.

I will verify this through the MIB browser.

[David Brousseau]

Bergonz hit the nail on the head. Thanks!

[David Brousseau]

Bergonz's hint at the formatting of the output was correct. The hex octets 0x4034 was being converted to the ascii string "@4" where the intended interpretation is bridge port 52 with a priority of 0x40.