Determining the likelihood of traffic being legitimately received at a proxy server in a cloud-based proxy service

1. A method for determining a likelihood of a packet having a particular source address being received at a particular one of a plurality of proxy servers that are anycasted to a same IP address, wherein the proxy servers are part of a cloud-based proxy service and are situated between a plurality of client computing devices accessing network resources and a plurality of origin servers that serve network resources, the method comprising:

receiving, from each of the plurality of proxy servers, one or more messages that indicate source IP addresses of packets received at that proxy server that are directed to the same IP address, wherein the proxy servers receive traffic at the same IP address as a result of one or more domains resolving to the same IP address, and wherein a first proxy server of the proxy servers receives packets directed to the same IP address as a result of an anycast protocol implementation selecting the first proxy server of the proxy servers as the closest in terms of routing protocol metric used to route traffic to the proxy servers;

determining, based on an historical analysis of the source IP addresses of packets received at the plurality of proxy servers as a result of the anycast protocol implementation as indicated in the one or more messages from each of the plurality of proxy servers, a likelihood of a packet having a particular source IP address being legitimately received at each of the proxy servers, wherein packets are likely to be legitimately received at each of the proxy servers when probabilities for each source-destination IP address pair determined using the historical analysis are above a threshold value;

transmitting, to each of the proxy servers, a message that indicates which source IP addresses of packets are not likely to be legitimately received at that proxy server based on the probabilities for each source-destination IP address pair determined using the historical analysis; and

responsive to a network event that affects the likelihood of a packet having a particular source IP address being legitimately received at each of the proxy servers, transmitting a message to the proxy servers that indicates a suspension of any rate limits that have been installed as a result of transmitting the messages to the proxy servers that indicate which source IP addresses of packets are not likely to be legitimately received at the proxy servers.

2. The method of claim 1 , wherein the message transmitted to each of the proxy servers includes a set of rules to rate limit packets received with source IP addresses that are not likely to be legitimately received by that proxy server.

3. The method of claim 1 , wherein the message transmitted to each of the proxy servers includes a set of rules to block packets received with source IP addresses that are not likely to be legitimately received by that proxy server.

4. The method of claim 1 , wherein the message transmitted to each of the proxy servers specifies the source IP addresses of packets that are likely to be legitimately received at that proxy server.

5. The method of claim 1 , wherein the message transmitted to each of the proxy servers specifies the source IP addresses of packets that are not likely to be legitimately received at that proxy server.

6. The method of claim 1 , wherein the step of receiving from each of the plurality of proxy servers the one or more messages that indicate source IP addresses of packets received at that proxy server that are directed to the same IP address, occurs only when the same IP address is not currently under a denial of service (DoS) attack.

7. The method of claim 1 , wherein the one or more messages received from each of the plurality of proxy servers further indicates a number of packets of each source IP address received at that proxy server.

8. The method of claim 1 , wherein the one or more messages are received as a result of a client-side script that is inserted by the proxy servers into web pages of domains that resolve to the same IP address, wherein the client-side script, when executed, causes a packet to be transmitted to the same IP address.

9. An apparatus, comprising:

a plurality of proxy servers that are anycasted to a same IP address, each of the plurality of proxy servers running on one or one or more physical devices, wherein each of the plurality of proxy servers is configured to perform the following:

receive packets at the same IP address as a result of one or more domains resolving to the same IP address, wherein this proxy server receives the packets at the same IP address as a result of an anycast protocol implementation selecting this one of the plurality of proxy servers as the closest in terms of routing protocol metric used to route traffic to the plurality of proxy servers;

transmit one or more messages to a central server computer that indicate source IP addresses of the received packets; and

receive, from the central server computer, a message that indicate source IP addresses of packets that are not likely to be legitimately received at that proxy server; and

install, based on the received message, one or more rules to rate limit packets that are received having a source IP address that is not likely to be legitimately received at that proxy server; and

the central server computer coupled with the plurality of proxy servers, wherein the central server computer is configured to perform the following:

receive, from each of the plurality of proxy servers, the one or more messages that indicate source IP addresses of the received packets;

determine, based on an historical analysis of the source IP addresses of packets received at the plurality of proxy servers as a result of the anycast protocol implementation as indicated in the one or more messages received from the plurality of proxy servers, a likelihood of a packet having a particular source IP address being legitimately received at each of the proxy servers, wherein packets are likely to be legitimately received at each of the proxy servers when probabilities for each source-destination IP address pair determined using the historical analysis are above a threshold value;

transmit, to each of the proxy servers, the message that indicates which source IP addresses of packets are not likely to be legitimately received at that proxy server based on the probabilities for each source IP address determined using the historical analysis; and

responsive to a network event that affects the likelihood of a packet having a particular source IP address being legitimately received at each of the proxy servers, transmit a message to the proxy servers that indicates a suspension of any rate limits that have been installed as a result of transmitting the messages to the proxy servers that indicate which source IP addresses of packets are not likely to be legitimately received at the proxy servers.

10. The apparatus of claim 9 , wherein the message transmitted to each of the proxy servers includes a set of rules to rate limit packets received with source IP addresses that are not likely to be legitimately received by that proxy server.

11. The apparatus of claim 9 , wherein the message transmitted to each of the proxy servers includes a set of rules to block packets received with source IP addresses that are not likely to be legitimately received by that proxy server.

12. The apparatus of claim 9 , wherein the message transmitted to each of the proxy servers specifies the source IP addresses of packets that are likely to be legitimately received at that proxy server.

13. The apparatus of claim 9 , wherein the message transmitted to each of the proxy servers specifies the source IP addresses of packets that are not likely to be legitimately received at that proxy server.

14. The apparatus of claim 9 , wherein the proxy servers are configured to transmit the one or more messages to the central server computer that indicate source IP addresses of the received packets only when the destination IP address of those packets is not-currently under a denial of service (DoS) attack.

15. The apparatus of claim 9 , wherein the one or more messages to be transmitted by each of the proxy servers further indicates a number of packets of each source IP address received at that proxy server.

16. The apparatus of claim 9 , wherein the one or more messages to be transmitted by each of the proxy servers are to be transmitted as a result of a client-side script that is inserted by the proxy servers into web pages of domains that resolve to the same IP address, wherein the client-side script, when executed, causes a packet to be transmitted to the same IP address.

17. A non-transitory computer-readable storage medium that provides instructions that, if executed by a processor, will cause said processor to perform operations for determining a likelihood of a packet having a particular source address being received at a particular one of a plurality of proxy servers that are anycasted to a same IP address, wherein the proxy servers are part of a cloud-based proxy service and are situated between a plurality of client computing devices accessing network resources and a plurality of origin servers that serve network resources, the operations comprising:

receiving, from each of the plurality of proxy servers, one or more messages that indicate source IP addresses of packets received at that proxy server that are directed to the same IP address, wherein the proxy servers receive traffic at the same IP address as a result of one or more domains resolving to the same IP address, and wherein a first proxy server of the proxy servers receives packets directed to the same IP address as a result of an anycast protocol implementation selecting the first proxy server of the proxy servers as the closest in terms of routing protocol metric used to route traffic to the proxy servers;

determining, based on an historical analysis of the source IP addresses of packets received at the plurality of proxy servers as a result of the anycast protocol implementation as indicated in the one or more messages from each of the plurality of proxy servers, a likelihood of a packet having a particular source IP address being legitimately received at each of the proxy servers, wherein packets are likely to be legitimately received at each of the proxy servers when probabilities for each source-destination IP address pair determined using the historical analysis are above a threshold value;

transmitting, to each of the proxy servers, a message that indicates which source IP addresses of packets are not likely to be legitimately received at that proxy server based on the probabilities for each source IP address determined using the historical analysis; and

responsive to a network event that affects the likelihood of a packet having a particular source IP address being legitimately received at each of the proxy servers, transmitting a message to the proxy servers that indicates a suspension of any rate limits that have been installed as a result of transmitting the messages to the proxy servers that indicate which source IP addresses of packets are not likely to be legitimately received at the proxy servers.

18. The non-transitory computer-readable storage medium of claim 17 , wherein the message transmitted to each of the proxy servers includes a set of rules to rate limit packets received with source IP addresses that are not likely to be legitimately received by that proxy server.