This indicates an attack attempt against a Denial of Service vulnerability in Quagga VTY service.
The vulnerability is caused by an error when the vulnerable software handles crafted messages. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system.
Quagga 0.93 - 1.1.0
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the latest update from the vendor.