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Analyzer Service Virtual Machine

The analyzer service virtual machine (analyzer-vm-console.qcow2) launches a Contrail-enhanced version of the network protocol analyzer Wireshark as the analyzer starts capturing mirror packets destined to the analyzer service.

Packet Format for Analyzer

The analyzer uses the PCAP format, which has these parts:

  • Global header

  • PCAP packet header

  • Packet data (original packet data)

The global header is added by the analyzer service by means of the Wireshark instance. The vRouter DP uses the configured UDP session to send mirrored packets to the analyzer, adding the PCAP packet header to the packet data as it sends it over the UDP socket to the analyzer.

The following additional information is also added to the packet data as metadata:

  • Captured host (IP address)

  • Ingress or egress

  • Action (Pass/Deny/...)

  • Source VN (fully qualified name)

  • Destination VN (fully qualified name)

In the existing PCAP, a network ID is added in the global header. The metadata (additional flow information) is added in front of the existing packet as follows.


| Global header | Packet header| Meta data |Packet data| Packet header| Meta data |Packet data|


Metadata Format

The metadata is in type-length-value (TLV) format as follows.

  1. Type: 1 Byte

  2. Length: 1 Byte

  3. Value: up to length


  1. 1 – Captured host IPv4 address

  2. 2 - Action field

  3. 3 – Source VN

  4. 4 – Destination VN

  5. 255 – TLV end

Captured host address

Length is 4 or 16 bytes based on IP address type

Action field

Length is 2 bytes. Multiple bits might be turned on, if there are more actions. Ingress or egress bit will be present in the Action field.

Source VN or Destination VN

Length is variable and up to 256 characters

TLV end

A special type 255 (0xFF) is used to identify the end of TLV entries. The TLV end must be last, at the end of the metadata.

Wireshark Changes

A plugin is added to the Wireshark code. The plugin parses the metadata and displays the packet fields; see example in Figure 1.

Figure 1: Wireshark Packet DisplayWireshark Packet Display

Troubleshooting Packet Display

Follow these steps if the packets are not displaying:

  1. Use tcpdump on the tap interfaces to see if packets are going towards the analyzer VM.

  2. Check introspect to see whether the flow action has mirror activity in it or not.