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Taikun OCP Guide

Table of Contents

Service function chaining

Service function chain (SFC) essentially refers to the
software-defined networking (SDN) version of policy-based routing (PBR).
In many cases, SFC involves security, although it can include a variety
of other features.

Fundamentally, SFC routes packets through one or more service
functions instead of conventional routing that routes packets using
destination IP address. Service functions essentially emulate a series
of physical network devices with cables linking them together.

A basic example of SFC involves routing packets from one location to
another through a firewall that lacks a “next hop” IP address from a
conventional routing perspective. A more complex example involves an
ordered series of service functions, each implemented using multiple
instances (VMs). Packets must flow through one instance and a hashing
algorithm distributes flows across multiple instances at each hop.

Architecture

All OpenStack Networking services and OpenStack Compute instances
connect to a virtual network via ports making it possible to create a
traffic steering model for service chaining using only ports. Including
these ports in a port chain enables steering of traffic through one or
more instances providing service functions.

A port chain, or service function path, consists of the
following:

  • A set of ports that define the sequence of service functions.
  • A set of flow classifiers that specify the classified traffic flows
    entering the chain.

If a service function involves a pair of ports, the first port acts
as the ingress port of the service function and the second port acts as
the egress port. If both ports use the same value, they function as a
single virtual bidirectional port.

A port chain is a unidirectional service chain. The first port acts
as the head of the service function chain and the second port acts as
the tail of the service function chain. A bidirectional service function
chain consists of two unidirectional port chains.

A flow classifier can only belong to one port chain to prevent
ambiguity as to which chain should handle packets in the flow. A check
prevents such ambiguity. However, you can associate multiple flow
classifiers with a port chain because multiple flows can request the
same service function path.

Currently, SFC lacks support for multi-project service functions.

The port chain plug-in supports backing service providers including
the OVS driver and a variety of SDN controller drivers. The common
driver API enables different drivers to provide different
implementations for the service chain path rendering.

Port chain architecture

Port chain model

See the networking-sfc
documentation
for more information.

Resources

Port chain

  • id – Port chain ID
  • project_id – Project ID
  • name – Readable name
  • description – Readable description
  • port_pair_groups – List of port pair group IDs
  • flow_classifiers – List of flow classifier IDs
  • chain_parameters – Dictionary of chain parameters

A port chain consists of a sequence of port pair groups. Each port
pair group is a hop in the port chain. A group of port pairs represents
service functions providing equivalent functionality. For example, a
group of firewall service functions.

A flow classifier identifies a flow. A port chain can contain
multiple flow classifiers. Omitting the flow classifier effectively
prevents steering of traffic through the port chain.

The chain_parameters attribute contains one or more
parameters for the port chain. Currently, it only supports a correlation
parameter that defaults to mpls for consistency with Open
vSwitch (OVS) capabilities. Future values for the correlation parameter
may include the network service header (NSH).

Port pair group

  • id – Port pair group ID
  • project_id – Project ID
  • name – Readable name
  • description – Readable description
  • port_pairs – List of service function port pairs

A port pair group may contain one or more port pairs. Multiple port
pairs enable load balancing/distribution over a set of functionally
equivalent service functions.

Port pair

  • id – Port pair ID
  • project_id – Project ID
  • name – Readable name
  • description – Readable description
  • ingress – Ingress port
  • egress – Egress port
  • service_function_parameters – Dictionary of service
    function parameters

A port pair represents a service function instance that includes an
ingress and egress port. A service function containing a bidirectional
port uses the same ingress and egress port.

The service_function_parameters attribute includes one
or more parameters for the service function. Currently, it only supports
a correlation parameter that determines association of a packet with a
chain. This parameter defaults to none for legacy service
functions that lack support for correlation such as the NSH. If set to
none, the data plane implementation must provide service
function proxy functionality.

Flow classifier

  • id – Flow classifier ID
  • project_id – Project ID
  • name – Readable name
  • description – Readable description
  • ethertype – Ethertype (IPv4/IPv6)
  • protocol – IP protocol
  • source_port_range_min – Minimum source protocol
    port
  • source_port_range_max – Maximum source protocol
    port
  • destination_port_range_min – Minimum destination
    protocol port
  • destination_port_range_max – Maximum destination
    protocol port
  • source_ip_prefix – Source IP address or prefix
  • destination_ip_prefix – Destination IP address or
    prefix
  • logical_source_port – Source port
  • logical_destination_port – Destination port
  • l7_parameters – Dictionary of L7 parameters

A combination of the source attributes defines the source of the
flow. A combination of the destination attributes defines the
destination of the flow. The l7_parameters attribute is a
place holder that may be used to support flow classification using layer
7 fields, such as a URL. If unspecified, the
logical_source_port and
logical_destination_port attributes default to
none, the ethertype attribute defaults to
IPv4, and all other attributes default to a wildcard
value.

Operations

Create a port chain

The following example uses the openstack command-line
interface (CLI) to create a port chain consisting of three service
function instances to handle HTTP (TCP) traffic flows from
192.0.2.11:1000 to 198.51.100.11:80.

  • Instance 1
    • Name: vm1
    • Function: Firewall
    • Port pair: [p1, p2]
  • Instance 2
    • Name: vm2
    • Function: Firewall
    • Port pair: [p3, p4]
  • Instance 3
    • Name: vm3
    • Function: Intrusion detection system (IDS)
    • Port pair: [p5, p6]

Note

The example network net1 must exist before creating
ports on it.

  1. Source the credentials of the project that owns the
    net1 network.

  2. Create ports on network net1 and record the UUID
    values.

    $ openstack port create p1 --network net1
    $ openstack port create p2 --network net1
    $ openstack port create p3 --network net1
    $ openstack port create p4 --network net1
    $ openstack port create p5 --network net1
    $ openstack port create p6 --network net1
  3. Launch service function instance vm1 using ports
    p1 and p2, vm2 using ports
    p3 and p4, and vm3 using ports
    p5 and p6.

    $ openstack server create --nic port-id=P1_ID --nic port-id=P2_ID vm1
    $ openstack server create --nic port-id=P3_ID --nic port-id=P4_ID vm2
    $ openstack server create --nic port-id=P5_ID --nic port-id=P6_ID vm3

    Replace P1_ID, P2_ID, P3_ID,
    P4_ID, P5_ID, and P6_ID with the
    UUIDs of the respective ports.

    Note

    This command requires additional options to successfully launch an
    instance. See the CLI
    reference
    for more information.

    Alternatively, you can launch each instance with one network
    interface and attach additional ports later.

  4. Create flow classifier FC1 that matches the
    appropriate packet headers.

    $ openstack sfc flow classifier create \
      --description "HTTP traffic from 192.0.2.11 to 198.51.100.11" \
      --ethertype IPv4 \
      --source-ip-prefix 192.0.2.11/32 \
      --destination-ip-prefix 198.51.100.11/32 \
      --protocol tcp \
      --source-port 1000:1000 \
      --destination-port 80:80 FC1

    Note

    When using the (default) OVS driver, the
    --logical-source-port parameter is also required

  5. Create port pair PP1 with ports p1 and
    p2, PP2 with ports p3 and
    p4, and PP3 with ports p5 and
    p6.

    $ openstack sfc port pair create \
      --description "Firewall SF instance 1" \
      --ingress p1 \
      --egress p2 PP1
    
    $ openstack sfc port pair create \
      --description "Firewall SF instance 2" \
      --ingress p3 \
      --egress p4 PP2
    
    $ openstack sfc port pair create \
      --description "IDS SF instance" \
      --ingress p5 \
      --egress p6 PP3
  6. Create port pair group PPG1 with port pair
    PP1 and PP2 and PPG2 with port
    pair PP3.

    $ openstack sfc port pair group create \
      --port-pair PP1 --port-pair PP2 PPG1
    $ openstack sfc port pair group create \
      --port-pair PP3 PPG2

    Note

    You can repeat the --port-pair option for multiple port
    pairs of functionally equivalent service functions.

  7. Create port chain PC1 with port pair groups
    PPG1 and PPG2 and flow classifier
    FC1.

    $ openstack sfc port chain create \
      --port-pair-group PPG1 --port-pair-group PPG2 \
      --flow-classifier FC1 PC1

    Note

    You can repeat the --port-pair-group option to specify
    additional port pair groups in the port chain. A port chain must contain
    at least one port pair group.

    You can repeat the --flow-classifier option to specify
    multiple flow classifiers for a port chain. Each flow classifier
    identifies a flow.

Update a port chain or
port pair group

  • Use the openstack sfc port chain set command to
    dynamically add or remove port pair groups or flow classifiers on a port
    chain.

    • For example, add port pair group PPG3 to port chain
      PC1:

      $ openstack sfc port chain set \
        --port-pair-group PPG1 --port-pair-group PPG2 --port-pair-group PPG3 \
        --flow-classifier FC1 PC1
    • For example, add flow classifier FC2 to port chain
      PC1:

      $ openstack sfc port chain set \
        --port-pair-group PPG1 --port-pair-group PPG2 \
        --flow-classifier FC1 --flow-classifier FC2 PC1

      SFC steers traffic matching the additional flow classifier to the
      port pair groups in the port chain.

  • Use the openstack sfc port pair group set command to
    perform dynamic scale-out or scale-in operations by adding or removing
    port pairs on a port pair group.

    $ openstack sfc port pair group set \
      --port-pair PP1 --port-pair PP2 --port-pair PP4 PPG1

    SFC performs load balancing/distribution over the additional service
    functions in the port pair group.

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