Redhat – Centos multiple NICs routing issue

Your routes and configuration look fine.

$: route -n
Destination // Gateway // Genmask // Flags // Metric // Ref // Use // Iface
66.*.*.0       0.0.0.0    255.255.255.248   U   1003      0   0     0  em2
0.0.0.0        66.*.*.1   0.0.0.0           UG     0      0   0     0  em2

The first route, 66.*.*.0/29 with gateway 0.0.0.0 tells your computer to use interface em2 and then make an arp request to find the hardware address of the host you're trying to reach. This is a "connected" route.

The second one is the default route, pointing at your default gateway through em2. If you need to send a packet in another network than 66.*.*.0/29, your computer will make an arp request to find 66.*.*.1 and then send the packets to it.

The only thing in your configuration that could be an issue is the NM_CONTROLLED=yes statement in /etc/sysconfig/network-scripts/ifcfg-em2. This tells the system that this interface is controlled by NetworkManager. This could interfere with your static configuration.

However, even without any default gateway you should be able to ping and ssh from the 66.*.*.0/29 subnet to your machine.

Check layer 1 first, and ensure that the cable is plugged on each side. Use leds on nic and switch, and check if the system sees it correctly:

# mii-tool
eth0: negotiated 1000baseT-FD flow-control, link ok

Then verify if any iptables are dropping the packets. Use iptables -L or iptables-save to check for any rules, and iptables -D <rule> to delete them. Pay attention to the default policy.

Also, on some systems, NetworkManager can configure ufw automatically, and I've had issues with static interface configuration that wasn't seen by NM and hence blocked by ufw.

Absolutely you can. You're looking for 802.1q tagging, which is the underpinning of multiple VLANs on a switch.

Configure your server-facing ports like this...

interface GigabitEthernet0/1
 ! tell the switch to encapsulate frames with dot1q on this trunk port
 switchport trunk encapsulation dot1q
 ! make this a trunk port unconditionally
 switchport mode trunk
 ! allow VLANs 220, 221, and 223 to be sent on this port
 switchport trunk allowed vlan 220,221,223
 ! send vlan 221 frames untagged
 ! you could omit this command, but you'll need to move your eth0 config to a subinterface as well
 switchport trunk native vlan 221
 ! this is an end-device, and doesn't need to be treated like a switch for spanning-tree
 spanning-tree portfast trunk
 ! remove the (ignored) access vlan setting, as this is now a trunk
 no switchport access vlan

On your Ubuntu server you'll need to configure the subinterfaces to be associated to each appropriate VLAN. This can be done manually like this ...

# create a new subinterface tied to dot1q vlan 221
ip link add link eth0 name eth0.221 type vlan id 221
# change the MTU to allow for the inserted dot1q tag (4 bytes)
ifconfig eth0 mtu 1504
# bring the new interface up
ifconfig eth0.221 up

Now you can associate the correct IP address to new interface eth0.221, along with the appropriate default gateway and subnet mask.

If this doesn't work for you, please include a pastebin link to your switch config as well as the output of "ip -d link show" on your Ubuntu server.

Hope this helps!