Mirroring Inbound TCP Traffic to a Single Network Interface

Solution Architecture

To mirror inbound TCP traffic from a mirror source (network interface) to a single mirror target (network interface), you can refer to the configurations in this section. In Figure 1, when ECS-test accesses ECS-source, you can create a mirror session to mirror inbound TCP traffic on ECS-source to ECS-target.

• Set the mirror source to Network-interface-s of ECS-source, indicating that the inbound TCP traffic on this network interface needs to be mirrored.
• Set the mirror target to Network-interface-t of ECS-target, indicating that the inbound TCP traffic on network-interface-s is mirrored to network-interface-t.
• Associate the mirror filter that has a rule for accepting inbound TCP traffic with the mirror session.

Figure 1 Mirroring inbound TCP traffic

Notes and Constraints

See Notes and Constraints.

Resource Planning

In this example, the VPC, subnet, EIP, and ECSs must be in the same region but can be in different AZs.

The following resource details are only for your reference. You can modify them if needed.

Table 1 Resource details for mirroring inbound TCP traffic

Resource	Quantity	Description
VPC and subnet	VPC: 1 Subnet: 1	VPC name: Set it as needed. In this example, VPC-A is used. VPC IPv4 CIDR block: Set it as needed. In this example, 192.168.0.0/16 is used. Subnet name: Set it as needed. In this example, Subnet-A01 is used. Subnet IPv4 CIDR block: Set it as needed. In this example, 192.168.0.0/24 is used.
ECS	3	Configure the ECSs as follows: Name: Set it as needed. In this example, the ECSs are named ECS-source, ECS-target, and ECS-test. ECS type: In this example, the type of ECS-source is General computing-plus c7t. Currently, only network interfaces of ECSs of certain types can be used as mirror sources. For details, see Notes and Constraints. There are no constraints on the type of ECS-target and ECS-test. Image: Set it as needed. In this example, public image Huawei Cloud EulerOS 2.0 Standard 64 bit is used. System disk: In this example, a general purpose SSD disk of 40 GiB is used. Data disk: Set it as needed. In this example, no data disk is used. Network VPC: Select a VPC. In this example, VPC-A is used. Subnet: Select a subnet. In this example, Subnet-A01 is used. Security group: In this example, the three ECSs are associated with the same security group (Sg-X). Ensure that all rules in Table 2 are added. If the ECSs are associated with different security groups, you also need to add additional rules. If ECS-test is associated with Sg-X and ECS-source is associated with Sg-A, add the rule in Table 3 to Sg-A to allow traffic from ECS-test. If ECS-source is associated with Sg-A but ECS-target is associated with Sg-B, add the rule in Table 4 to Sg-B to allow UDP packets encapsulated by the mirror source to access the mirror target over port 4789. EIP: Select Not required. Private IP address: In this example, use 192.168.0.230 for ECS-source, 192.168.0.164 for ECS-target, and 192.168.0.161 for ECS-test.
EIP	1	Billing Mode: Set it as needed. In this example, Pay-per-use is used. EIP Name: Set it as needed. In this example, EIP-A is used. EIP: The EIP is randomly assigned. In this example, 124.X.X.187 is used.
Mirror filter	1	Name: Set it as needed. In this example, mirror-filter-A is used. Inbound rule: Add the inbound rule in Table 5. This rule allows TCP packets from ECS-test to ECS-source over port 1234 to be mirrored.
Mirror session	1	Basic Information Name: Set it as needed. In this example, mirror-session-A is used. Priority: Set it as needed. In this example, 1 is used. VNI: Set it as needed. In this example, 1 is used. Packet Length: Set it as needed. In this example, 96 is used. Mirror Session: Enable it to mirror the traffic from the mirror source. Associate Mirror Filter: Set it as needed. In this example, mirror-filter-A is used. Associate Mirror Sources: Set it as needed. In this example, the private IP address (192.168.0.230) of the network interface of ECS-source is used. Associate Mirror Target Type: Network interface Network interface: Set it as needed. In this example, the private IP address (192.168.0.164) of the network interface of ECS-target is used.

Table 2 Security group Sg-X rules

Direction	Action	Type	Protocol & Port	Source/Destination	Description
Inbound	Allow	IPv4	TCP: 22	Source: 0.0.0.0/0	Allows remote logins to Linux ECSs over SSH port 22.
Inbound	Allow	IPv4	TCP: 3389	Source: 0.0.0.0/0	Allows remote logins to Windows ECSs over RDP port 3389.
Inbound	Allow	IPv4	All	Source: current security group (Sg-X)	Allows the ECSs in this security group to communicate with each other using IPv4 addresses.
Inbound	Allow	IPv6	All	Source: current security group (Sg-X)	Allows the ECSs in this security group to communicate with each other using IPv6 addresses.
Outbound	Allow	IPv4	All	Destination: 0.0.0.0/0	Allows ECSs in this security group to access the Internet using IPv4 addresses.
Outbound	Allow	IPv6	All	Destination: ::/0	Allows ECSs in this security group to access the Internet using IPv6 addresses.

If the source of an inbound rule is set to 0.0.0.0/0, all external IP addresses are allowed to remotely log in to your cloud server. Exposing port 22 or 3389 to the public network will leave your instances vulnerable to network risks. To address this issue, set the source to a known IP address, for example, the IP address of your local PC.

Table 3 Security group Sg-A rules

Direction	Action	Type	Protocol & Port	Source	Description
Inbound	Allow	IPv4	TCP: 1234	Private IP address of the ECS that accesses the mirror source. In this example, the private IP address of ECS-test is used: 192.168.0.161/32	Allows TCP packets from ECS-test to ECS-source over port 1234.

Table 4 Security group Sg-B rules

Direction	Action	Type	Protocol & Port	Source	Description
Inbound	Allow	IPv4	UDP: 4789	The private IP address of mirror source ECS-source: 192.168.0.230/32	Allows UDP packets encapsulated by ECS-source to access ECS-target over port 4789.

Table 5 Inbound rules of the mirror filter

Direction	Priority	Protocol	Action	Type	Source	Source Port Range	Destination	Destination Port Range
Inbound	1	TCP	Accept	IPv4	The private IP address of ECS-test: 192.168.0.161/32	All	The private IP address of ECS-source: 192.168.0.230/32	Port of ECS-source: 1234-1234

Procedure

Figure 2 shows the procedure required to mirror inbound TCP traffic to a single network interface.

Figure 2 Mirroring inbound TCP traffic

Step 1: Create Cloud Resources

1. Create a VPC and subnet.

   For details, see Creating a VPC and Subnet.

2. Create three ECSs.

   For details, see Purchasing a Custom ECS.

3. Assign an EIP.

   For details, see Assigning an EIP.

Step 2: Create a Mirror Filter and a Mirror Session

1. Create a mirror filter.

   For details, see Creating a Mirror Filter.

2. Create a mirror session, and associate the mirror filter, mirror source, and mirror target with this mirror session.

   For details, see Creating a Mirror Session.

Step 3: Install Netcat (nc) to Simulate Traffic

The nc utility reads and writes data across network connections using TCP or UDP. It is usually used to test ports for accessibility. You need to install nc on both ECS-source and ECS-test.

1. Install nc on ECS-source.
   1. Bind the EIP to ECS-source to connect to the Internet for downloading the nc utility.

      For details, see Binding an EIP to an ECS.

   2. Remotely log in to ECS-source.

      For details, see How Do I Log In to My ECS?

   3. Run the following commands in sequence to install nc:

      sudo yum update

      Information similar to the following is displayed:

      [root@ecs-source ~]# sudo yum update
      HCE 2.0 base                                                                                                                                                 55 MB/s | 6.1 MB     00:00    
      HCE 2.0 updates                                                                                                                                              98 MB/s |  14 MB     00:00    
      Last metadata expiration check: 0:00:01 ago on Tue 10 Sep 2024 05:54:28 PM CST.
      Dependencies resolved.
      Nothing to do.
      Complete!

      sudo yum install nc

      If information similar to the following is displayed, enter y as prompted and press Enter:

      [root@ecs-source ~]# sudo yum install nc
      Last metadata expiration check: 0:00:12 ago on Tue 10 Sep 2024 05:54:28 PM CST.
      Dependencies resolved.
      ...
      Install  2 Packages
      
      Total download size: 6.1 M
      Installed size: 25 M
      Is this ok [y/N]: y
      Downloading Packages:
      ...    
      Importing GPG key 0xA8DEF926:
       Userid     : "HCE <support@huaweicloud.com>"
       Fingerprint: C1BA 9CD4 9D03 A206 E241 F176 28DA 5B77 A8DE F926
       From       : http://repo.huaweicloud.com/hce/2.0/updates/RPM-GPG-KEY-HCE-2
      Is this ok [y/N]: y
      ...
      Installed:
        libssh2-1.10.0-2.r10.hce2.x86_64                                                               nmap-2:7.92-2.r4.hce2.x86_64                                                              
      
      Complete!

   4. Unbind the EIP from ECS-source after nc is installed.

      For details, see Unbinding an EIP.

2. Repeat 1.a to 1.d on ECS-test.
3. Release the EIP.

   For details, see Unbinding an EIP. If you do not release the EIP, the EIP will continue to be billed.

Step 3: Check Whether the Mirror Session Works

1. Establish a TCP connection between ECS-source and ECS-test.

   Send TCP packets from ECS-test to ECS-source and check whether ECS-source can receive the packets.

   1. Run the following command on ECS-source to listen to its port 1234:

      nc -l <listening-port-of-mirror-source-ECS-source>

      Example command:

      nc -l 1234

      If the command output is empty, the port is opened for listening.

   2. Run the following command on ECS-test to establish a TCP connection between ECS-source and ECS-test:

      nc <private-IP-address-of-mirror-source-ECS-source> <listening-port-of-mirror-source-ECS-source>

      Example command:

      nc 192.168.0.230 1234

      The command output is empty. Enter any information (for example, hello) on ECS-test and press Enter to check whether the TCP connection is successfully established.

      [root@ecs-test ~]# nc 192.168.0.230 1234
      hello

   3. Check whether ECS-source can receive information from ECS-test.
      If information similar to the following is displayed, the TCP connection is successfully established.

      [root@ecs-source ~]# nc -l 1234
      hello

2. Check whether the inbound packets on ECS-source can be mirrored to ECS-target.
   When ECS-test sends a TCP packet to ECS-source, run tcpdump to check whether ECS-target can receive the packet. If ECS-target receives the packet, the mirror session works.

   1. Remotely log in to ECS-target.

      For details, see How Do I Log In to My ECS?

   2. Run the following command on ECS-target to view its network interface name:

      ifconfig

      Information similar to the following is displayed. In this example, the network interface of the mirror target is eth0.

      [root@ecs-target ~]# ifconfig
      eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
              inet 192.168.0.164  netmask 255.255.255.0  broadcast 192.168.0.255
              inet6 fe80::f816:3eff:fe7e:d67a  prefixlen 64  scopeid 0x20<link>
              ether fa:16:3e:7e:d6:7a  txqueuelen 1000  (Ethernet)
              RX packets 29043  bytes 32268398 (30.7 MiB)
              RX errors 0  dropped 0  overruns 0  frame 0
              TX packets 13811  bytes 3961116 (3.7 MiB)
              TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
      ...

   3. Run the following command on ECS-target to check whether it can receive packets:

      tcpdump -i <network-interface-name-of-the-mirror-target> udp port 4789 -nne

      Example command:

      tcpdump -i eth0 udp port 4789 -nne

      Information similar to the following is displayed:

      [root@ecs-target ~]# tcpdump -i eth0 udp port 4789 -nne
      dropped privs to tcpdump
      tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
      listening on eth0, link-type EN10MB (Ethernet), snapshot length 262144 bytes

   4. Enter any information (for example, 12345) on ECS-test and press Enter to send TCP packets to ECS-source.
      Information similar to the following is displayed:

      [root@ecs-test ~]# nc 192.168.0.230 1234
      hello
      12345

   5. Check whether ECS-source can receive information from ECS-test.
      If information similar to the following is displayed, ECS-source can receive information from ECS-test:

      [root@ecs-source ~]# nc -l 1234
      hello
      12345

   6. Check whether ECS-target can receive packets.
      Information similar to the following is displayed. You can view the packet of 12345 sent by ECS-test after running tcpdump. vni 1 is the identifier of the mirror session, indicating that ECS-target can receive the packet through the mirror session. The packet content has two parts. For details, see Table 6.

      [root@ecs-target ~]# tcpdump -i eth0 udp port 4789 -nne
      dropped privs to tcpdump
      tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
      listening on eth0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
      19:12:25.839624 fa:16:3e:d1:6b:5d > fa:16:3e:7e:d6:7a, ethertype IPv4 (0x0800), length 122: 192.168.0.230.32838 > 192.168.0.164.4789: VXLAN, flags [I] (0x08), vni 1
      fa:16:3e:7e:d6:77 > fa:16:3e:7e:d6:bc, ethertype IPv4 (0x0800), length 72: 192.168.0.161.38944 > 192.168.0.230.1234: Flags [P.], seq 2063075043:2063075049, ack 1116663338, win 502, options [nop,nop,TS val 969673134 ecr 605179348], length 6

      Table 6 Packet description

      Packet Example	Packet Description
      19:12:25.839624 fa:16:3e:d1:6b:5d > fa:16:3e:7e:d6:7a, ethertype IPv4 (0x0800), length 122: 192.168.0.230.32838 > 192.168.0.164.4789: VXLAN, flags [I] (0x08), vni 1	VXLAN packet encapsulated by Traffic Mirroring. Packet format: <Timestamp><SMacAddr><DMacAddr><EthernetType><Length><Sip><Sport><Dip><Dport><VXLAN Flags><VNI> Fields in the encapsulated packet: Timestamp: Time when a packet is obtained. It is generated by tcpdump. SMacAddr: MAC address of the source instance of VXLAN packets. In this example, it is the MAC address of the gateway instance. DMacAddr: MAC address of the target instance of VXLAN packets. In this example, it is the MAC address of the mirror target instance. EthernetType: indicates the Ethernet type of a packet. 0x0800 indicates that the protocol is IPv4. Length: packet length Sip: Mirror source address Sport: Mirror source port Dip: Mirror target address Dport: Mirror target port, which is usually port 4789 that receives VXLAN packets VXLAN Flags: The value is usually 0x08, indicating a VXLAN packet. VNI: VXLAN network identifier of a mirror session
      fa:16:3e:7e:d6:77 > fa:16:3e:7e:d6:bc, ethertype IPv4 (0x0800), length 72: 192.168.0.161.38944 > 192.168.0.230.1234: Flags [P.], seq 2063075043:2063075049, ack 1116663338, win 502, options [nop,nop,TS val 969673134 ecr 605179348], length 6	Original packet The original packet field is general network knowledge and is not described in detail herein.