May be if you had properly complained to your ISP that you are facing a DOS attack, they could help you fish out the source IPs and block them before the attack gets to you0r pipe
There are also techniques to mitigate against this attacks such as setting embryonic limits on the firewalls that support such feature, agreeing a CIR (Committed Information Rate) on your link with your ISP to try and limit Ping traffic, etc going down the link, it’s like a QoS on that link. If you are using a Cisco pix one can specify a function called emb_lim (embryonic limit) because the attack sets the target host in an embryonic state emb_lim (Optional) Specifies the maximum number of embryonic connections per host. The default is 0, which means unlimited embryonic connections. Limiting the number of embryonic connections protects you from a DoS attack. The security appliance uses the embryonic limit to trigger TCP Intercept, which protects inside systems from a DoS attack perpetrated by flooding an interface with TCP SYN packets. An embryonic connection is a connection request that has not finished the necessary handshake between source and destination. This option does not apply to outside NAT. The security appliance only tracks connections from a higher security interface to a lower security interface. If you set the embryonic limit for outside NAT, the embryonic limit will be ignored.
