LVS and Synproxy

The SYNPROXY module deploys TCP SYN cookies to establish a TCP connection terminated on a third party device located behind the HAProxy ALOHA. It relies on the conntrack module to translate sequence numbers.

The diagram below show how sequence numbers are translated from Y (client to HAProxy ALOHA) to Z (HAProxy ALOHA to server):

Objective Jump to heading #

In HAProxy ALOHA, the SYNPROXY module is mainly used for integration with PacketShield to provide protection against packet flood attacks in the following cases:

• Traffic routed through HAProxy ALOHA

• Load balancing at Layer 4 in NAT mode

• Load balancing at Layer 4 in DSR mode if the server-to-client traffic is routed through HAProxy ALOHA

  Info

  PacketShield requires the TCP connection to terminate locally, which the SYNPROXY module emulates.

Configuring TCP SYNPROXY Jump to heading #

Requirements Jump to heading #

Configure the conntrack module Jump to heading #

In the HAProxy ALOHA Services tab, edit the service settings to add the following setting to the conntrack service:

text
sysctl tcp_loose=0

text
sysctl tcp_loose=0

The sysctl command prevents conntrack from accepting packets as NEW packets and allowing SYNPROXY to work.

To make the configuration change persist after a reboot, execute config save.

Configure LVS Jump to heading #

With LVS, the use of the SYNPROXY module leads to a SYN/SYN-ACK loop between clients and the load balancer.

To circumvent this issue, we use LVS in conjunction with conntrack.

• In the HAProxy ALOHA Services tab, edit the service settings to add the following setting to the LVS service:

  text
  conntrack

  text
  conntrack

To make the configuration change persist after a reboot, execute config save.

SYNPROXY syntax rule Jump to heading #

text
<chain> [conditions of application] [TCP options]

text
<chain> [conditions of application] [TCP options]

Available chains Jump to heading #

Conditions of application Jump to heading #

TCP options Jump to heading #

Configuring SYNPROXY module Jump to heading #

1. In the HAProxy ALOHA Services tab, edit a service configuration.

2. In the text area, create your rules.

3. To make the configuration change persist after a reboot, go to the Setup tab and click Save in the Configuration section.

Configuration examples Jump to heading #

Protect HTTP and HTTPs services managed by HAProxy or LVS running in HAProxy ALOHA:

text
input dst 10.0.0.1 dstport 80 iface eth0 wscale 3
input dst 10.0.0.1 dstport 443 iface eth0 wscale 3

text
input dst 10.0.0.1 dstport 80 iface eth0 wscale 3
input dst 10.0.0.1 dstport 443 iface eth0 wscale 3

Protect HTTP and HTTPs services hosted by cloud service VMs located behind HAProxy ALOHA:

text
forward dstport 80 iface eth0 wscale 3
forward dstport 443 iface eth0 wscale 3

text
forward dstport 80 iface eth0 wscale 3
forward dstport 443 iface eth0 wscale 3