Configure an ENI

Background information

If your instance is running an image not shown in the preceding list, and you want to attach an ENI to your instance, you must manually configure the ENI to be supported. This topic uses an instance running CentOS 7.2 64-bit as an example to describe how to configure an ENI manually.

Prerequisite

You have attached an ENI to an ECS instance.

Procedure

To configure an ENI manually, follow these steps:

1. Use the DescribeNetworkInterfaces interface or log on to the ECS console to obtain the following attributes of the ENI: the primary private IP address, subnet mask, the default route, and the MAC address. To obtain these attributes in the ECS console, follow these steps:
   1. Log on to the  ECS console.
   2. Find the target ENI and obtain its primary private IP address, subnet mask, default route, and MAC address. Example:

      
      eth1 10.0.0.20/24 10.0.0.253 00: 16: 12: E7: 27
      eth2 10.0.0.21/24 10.0.0.253 00: 16: 12: 16: EC

2. Connect to the ECS instance.
3. Run the following command to generate the config file: cat /etc/sysconfig/network-scripts/ifcfg-[network interface name in the OS].
   Note

   • Pay attention to the relation between the network interface name in the OS and the MAC address.
   • Pay attention to the relation between the network interface name in the OS and the MAC address. The default route must be set to  DEFROUTE=no . Other editions must have the same configuration. Note that running the ifup command may change the active default route configuration after configuring the network interface.
   • Example:

     # cat /etc/sysconfig/network-scripts/ifcfg-eth1 
     DEVICE=eth1
     BOOTPROTO=dhcp
     ONBOOT=yes
     TYPE=Ethernet
     USERCTL=yes
     PEERDNS=no
     IPV6INIT = No
     PERSISTENT_DHCLIENT = Yes
     HWADDR=00:16:3e:12:e7:27
     DEFROUTE=noDefroute = No

4. To start the network interface, follow these steps:
   1. Run the ifup [network interface name in the OS]  command to start the dhclient process, and initiate a DHCP request. Example:

      # ifup eth1
      # ifup eth2

   2. After a response is received, run the ip a  a command to check the IP allocation on the network interfaces, which must match with the information displayed on the ECS console. Example:

      # ip a
      1: lo: mtu 65536 qdisc noqueue state UNKNOWN qlen 1
      link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
      inet 127.0.0.1/8 scope host loInet 125.0.0.1/8 Scope host Lo
      valid_lft forever preferred_lft forever
      2: eth0: mtu 1500 qdisc pfifo_fast state UP qlen 10002: eth0: MTU 1500 qdisc glasstate up qlen 1000
      link/ether 00:16:3e:0e:16:21 brd ff:ff:ff:ff:ff:ff
      Inet 10.0.0.19/24 BRD glasscope Global Dynamic eth0
      valid_lft 31506157sec preferred_lft 31506157secValid_lft 31506157sec preferred_lft 31506157sec
      3: eth1: MTU 1500 qdisc glasstate up qlen 1000
      link/ether 00:16:3e:12:e7:27 brd ff:ff:ff:ff:ff:ff
      inet 10.0.0.20/24 brd 10.0.0.255 scope global dynamic eth1Inet 10.0.0.20/24 BRD glasscope Global Dynamic eth1
      Valid_lft 31525994sec preferred_lft 31525994sec
      4: eth2: MTU 1500 qdisc glasstate up qlen 1000
      Link/ether 00: 16: Rye: 12: 16: ec brd ff: FF: FF
      inet 10.0.0.21/24 brd 10.0.0.255 scope global dynamic eth2
      valid_lft 31526009sec preferred_lft 31526009sec

5. Set the metric for each network interface in the route table. In this example, set the metric parameters of eth1 and eth2 as follows.

   eth1: gw: 10.0.0.253 metric: 1001
   eth2: gw: 10.0.0.253 metric: 1002

   1. Run the following command to set the metric parameters.

      # Ip-4 route add default via glasdev eth1 metric 1001
      # ip -4 route add default via 10.0.0.253 dev eth2 metric 1002

   2. Run the route -n command to check whether the configuration is successful. Example:

      # route -n
      Kernel IP routing table
      Destination Gateway Genmask Flags Metric Ref Use Iface
      0.0.0.0 10.0.0.253 0.0.0.0 UG 0 0 0 eth0
      0.0.0.0 10.0.0.253 0.0.0.0 UG 1001 0 0 eth1
      0.5.0.0 10.0.0.253 ug ub1002 0 0 eth2
      10.0.0.0 0.5.0.0 255.25.25.0 u 0 0 0 eth0
      10.0.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
      10.0.0.0 0.5.0.0 255.25.25.0 u 0 0 0 eth2
      169.254.0.0 0.0.0 255.0.0 U 1002 0 0 eth0
      169.254.0.0 0.0.0.0 255.255.0.0 U 1003 0 0 eth1
      169.254.0.0 0.0.0.0 255.255.0.0 U 1004 0 0 eth2169.254.0.0 0.0.0 255.0.0 U 1004 0 0 eth2

6. To build a route table, follow these steps:
   Note We recommend that you use the metric value as the route table name.
   1. Run the following command to build a route table.

      # ip -4 route add default via 10.0.0.253 dev eth1 table 1001
      # Ip-4 route add default via glasdev eth2 table 1002

   2. Run the following command to check whether the route table is built successfully.

      # ip route list table 1001
      default via 10.0.0.253 dev eth1
      # ip route list table 1002
      default via 10.0.0.253 dev eth2

7. Configure the policy routing.
   1. Run the following command to configure the policy routing.

      # ip -4 rule add from 10.0.0.20 lookup 1001
      # ip -4 rule add from 10.0.0.21 lookup 1002

   2. Run ip rule list to view the routing rules.

      # ip rule list
      0: from all lookup local
      32764: from 10.0.0.21 lookup 1002
      32765: from 10.0.0.20 lookup 1001
      32766: from all lookup main
      32767: from all lookup default

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