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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
WoJ
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eranga
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  • 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 04:29

1 Answers1

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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.

eranga
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