Routing Policies for Multi-NIC Appliances

SUMMARY

Routing Policies for Multi-NIC Appliances

ISSUE

For a deployment where a VBA (usually the Presentation and/or Management VBA) is configured to use two networks, the network active on interface eth0 will provide the default route for any address without an explicit route. As an example (Figure1):

Figure 1:
User-added image

The VmWare/Xen/HyperV host is using 10.10.95.0/24.
The Presentation VBA (one NIC, eth0) is using 10.10.133.0/24.
The Management VBA (two NICs); eth0 is using 10.10.133.0/24, eth1 is using 172.28.0.0/24.
Engine VBA One (one NIC, eth0) is using 10.10.133.0/24.
Engine VBA Two (one NIC, eth0) is using 172.28.0.0/24.

The routing table on the Presentation and Engine One VBAs will look like the following (assuming 10.10.133.1 is the gateway):

Kernel IP routing table  Destination Gateway Genmask Flags Metric Ref Use Iface  0.0.0.0 10.10.133.1 0.0.0.0 UG 0 0 0 eth0  10.10.133.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

The routing table on the Management VBA will look as follows (using the above assumption for eth0 and 172.28.0.1 as the gateway for eth1):

Kernel IP routing table  Destination Gateway Genmask Flags Metric Ref Use Iface  0.0.0.0 10.10.133.1 0.0.0.0 UG 0 0 0 eth0  0.0.0.0 172.28.0.1 0.0.0.0 UG 100 0 0 eth1  10.10.133.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0  172.28.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 

or

Kernel IP routing table  Destination Gateway Genmask Flags Metric Ref Use Iface  0.0.0.0 10.10.133.1 0.0.0.0 UG 0 0 0 eth0  10.10.133.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0  172.28.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1

The routing table for Engine Two VBA will look as follows:

Kernel IP routing table  Destination Gateway Genmask Flags Metric Ref Use Iface  0.0.0.0 172.28.0.1 0.0.0.0 UG 0 0 0 eth0  172.28.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 

Given that all Engine VBAs need network connectivity to the host (10.10.95.0/24 in the above example), the route to the host network:

  • must be provided by the default gateway
    or
  • must be explicitly added (i.e. sudo route add -net 10.10.95.0/24 gw 172.28.0.1)

If the latter is chosen, the preferred method of persisting the route through a reboot is to include the 'route add' command in /etc/rc.local, as opposed to using the 'up' or 'post-up' stanza in /etc/network/interfaces (as shown here: http://www.cyberciti.biz/faq/setting-up-an-network-interfaces-file/).

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