This paper presents a SNMP-based Monitoring Agentsfor Multi-Constrain Resource Scheduling in Grids(SBLOMARS) as an effective solution for resource usagemonitoring in virtual network environments. SBLOMARS isdifferent to current large-scale distributed monitoring systems inthree essential aspects: Firstly, it reaches a high level ofgenerality by the integration of the SNMP protocol and thus,facilitates to handle heterogeneous operating platforms.Secondly, it is able to self-configure the polling periods of theresources to be monitored depending of network context andfinally, it makes use of dynamic software structures to interfacewith third parties, allowing to be deployed in a wide range ofdevices, from simple mobile access devices to robustmultiprocessor systems or clusters with even multiple hard disksand storage partitions. SBLOMARS has been deployed inEmanicsLab, a virtual laboratory constituted by fourteen nodesdistributed in seven European Universities. Although theresearch is not yet concluded, available results confirm itssuitability to deal with the challenges of monitoring virtualnetworks.