Resolved Adding a LAN interface shuts down traffic on primary WAN interface

[UnS3eN]

Hi,

My current Plesk installation is currently configured to have 2 WAN addresses via a separate vSwitch.
I'm trying to add a second interface linked to my LAN vSwitch so I could access the LAN and the VPN from Plesk without having to go through the firewalls via an external connection.
- eth0 is up and has WAN IP 1 and WAN IP 2
- eth1 is down (to have LAN IP)

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
    link/ether MAC1 brd ff:ff:ff:ff:ff:ff
    inet WAN_IP1/29 brd WAN_BRD scope global eth0
    inet WAN_IP2/29 brd WAN_BRD scope global secondary eth0
    inet6 IPV6/64 scope link
       valid_lft forever preferred_lft forever
3: eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN qlen 1000
    link/ether MAC2 brd ff:ff:ff:ff:ff:ff

As soon as I bring up eth1, all traffic on eth0 dies (including SSH sessions, web hosting, DNS... everything). Surely this is not intended behaviour.

Any ideas?

 

[AYamshanov]

Hi UnS3eN,

Are WAN_IP1 and WAN_IP2 from different /29 networks? But I don't think it can be the issue.

Could some DHCP-server offer an IP-address and default gateway to eth1? After that, the system applies these settings and starts work with another IP-address with the Internet.

Could you bring up eth1 and check `ifconfig`, `netstat -rn`, `traceroute`, logs, etc.?

 

[UnS3eN]

Solved. Managed to solve the issue last night, at lest temporarily.

Are WAN_IP1 and WAN_IP2 from different /29 networks? But I don't think it can be the issue.

No, these are 2 addresses from the the same /29 subnet. This is definitely not the issue.

Could some DHCP-server offer an IP-address and default gateway to eth1?

Yup. That's exactly what it was. LAN interface requested DHCP lease and overwrote the default route.

Managed to get to the bottom of it after posting here. LAN DHCP lease was switching default route to eth1, killing all WAN traffic.

Solution:
Assign static IP to the additional interface - eth1 (BOOTPROTO=static)
Create static routing for both interfaces:
/etc/sysconfig/network-scripts/route-eth0
/etc/sysconfig/network-scripts/route-eth1

Default route for eth0 (WAN)
LAN and VPN routes for eth1

Seems to be working for now.