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Our gateway is a router which redirects all browsing traffic to a proxy server (Ubuntu 14.04.3). Proxy server then process and sends the traffic back to the router through a different interface. Proxy is also connected to the LAN .

Some computers in the LAN routes it's traffic directly to 192.168.0.2 which is the proxy server disregarding the default gateway (192.168.0.1) set in the network settigns. This has only identified with computers with static IP's for the moment. DHCP users do not have a problem. What could be the reason for this? How could we avoid this behaviour? Find a basic diagram of the network below.

Diagram

Routing table of a machine with static IP

Active Routes: Network Destination Netmask Gateway Interface Metric 0.0.0.0 0.0.0.0 192.168.0.1 192.168.0.179 276 127.0.0.0 255.0.0.0 On-link 127.0.0.1 306 127.0.0.1 255.255.255.255 On-link 127.0.0.1 306 127.255.255.255 255.255.255.255 On-link 127.0.0.1 306 169.254.0.0 255.255.0.0 On-link 192.168.0.179 296 169.254.255.255 255.255.255.255 On-link 192.168.0.179 276 192.168.0.0 255.255.255.0 On-link 192.168.0.179 276 192.168.0.179 255.255.255.255 On-link 192.168.0.179 276 192.168.0.255 255.255.255.255 On-link 192.168.0.179 276 224.0.0.0 240.0.0.0 On-link 127.0.0.1 306 224.0.0.0 240.0.0.0 On-link 192.168.0.179 276 255.255.255.255 255.255.255.255 On-link 127.0.0.1 306

255.255.255.255 255.255.255.255 On-link 192.168.0.179 276

Persistent Routes: Network Address Netmask Gateway Address Metric 0.0.0.0 0.0.0.0 192.168.0.1 Default

Routing table of a DHCP machine

Active Routes:

Network Destination Netmask Gateway Interface Metric 0.0.0.0 0.0.0.0 192.168.2.1 192.168.2.165 10 127.0.0.0 255.0.0.0 On-link 127.0.0.1 306 127.0.0.1 255.255.255.255 On-link 127.0.0.1 306 127.255.255.255 255.255.255.255 On-link 127.0.0.1 306 192.168.2.0 255.255.255.0 On-link 192.168.2.165 266 192.168.2.165 255.255.255.255 On-link 192.168.2.165 266 192.168.2.255 255.255.255.255 On-link 192.168.2.165 266 224.0.0.0 240.0.0.0 On-link 127.0.0.1 306 224.0.0.0 240.0.0.0 On-link 192.168.2.165 266 255.255.255.255 255.255.255.255 On-link 127.0.0.1 306 255.255.255.255 255.255.255.255 On-link 192.168.2.165 266

  • Perhaps you could post the routing tables for a dhcp and static client? "netstat -rn" for *nix type clients, "route print" for Windows clients. – Brandon Xavier Aug 26 '15 at 11:50
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    How does the router "redirect" this traffic? If it's using an ICMP redirect then that should tell the clients to add a route to their routing table for the proxy server, which would explain this behavior. – joeqwerty Aug 26 '15 at 12:15
  • We uce ACL's to match traffic coming from LAN destined towards ports 80 and 443 , then set next hop to the proxy server(192.168.0.2). – eranga Aug 28 '15 at 4:29
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We managed to address this issue thanks to the tip given by joeqwerty. We were not using ICMP redirects to redirect the traffic. However both the Proxy server and the Router were sending ICMP redirects to the clients. Since neither of the devices had any use for this behaviour, we disabled ICMP redirects in both the devices and the issue never came back.

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