Virtual Routing and Forwarding (VRF)
  ====================================
  The VRF device combined with ip rules provides the ability to create virtual
  routing and forwarding domains (aka VRFs, VRF-lite to be specific) in the
  Linux network stack. One use case is the multi-tenancy problem where each
  tenant has their own unique routing tables and in the very least need
  different default gateways.
  
  Processes can be "VRF aware" by binding a socket to the VRF device. Packets
  through the socket then use the routing table associated with the VRF
  device. An important feature of the VRF device implementation is that it
  impacts only Layer 3 and above so L2 tools (e.g., LLDP) are not affected
  (ie., they do not need to be run in each VRF). The design also allows
  the use of higher priority ip rules (Policy Based Routing, PBR) to take
  precedence over the VRF device rules directing specific traffic as desired.
  
  In addition, VRF devices allow VRFs to be nested within namespaces. For

  example network namespaces provide separation of network interfaces at the
  device layer, VLANs on the interfaces within a namespace provide L2 separation
  and then VRF devices provide L3 separation.

  
  Design
  ------
  A VRF device is created with an associated route table. Network interfaces
  are then enslaved to a VRF device:
  
           +-----------------------------+
           |           vrf-blue          |  ===> route table 10
           +-----------------------------+
              |        |            |
           +------+ +------+     +-------------+
           | eth1 | | eth2 | ... |    bond1    |
           +------+ +------+     +-------------+
                                    |       |
                                +------+ +------+
                                | eth8 | | eth9 |
                                +------+ +------+
  
  Packets received on an enslaved device and are switched to the VRF device

  in the IPv4 and IPv6 processing stacks giving the impression that packets
  flow through the VRF device. Similarly on egress routing rules are used to
  send packets to the VRF device driver before getting sent out the actual
  interface. This allows tcpdump on a VRF device to capture all packets into
  and out of the VRF as a whole.[1] Similarly, netfilter[2] and tc rules can be
  applied using the VRF device to specify rules that apply to the VRF domain
  as a whole.

  
  [1] Packets in the forwarded state do not flow through the device, so those
      packets are not seen by tcpdump. Will revisit this limitation in a
      future release.

  [2] Iptables on ingress supports PREROUTING with skb->dev set to the real
      ingress device and both INPUT and PREROUTING rules with skb->dev set to
      the VRF device. For egress POSTROUTING and OUTPUT rules can be written
      using either the VRF device or real egress device.

  
  Setup
  -----
  1. VRF device is created with an association to a FIB table.
     e.g, ip link add vrf-blue type vrf table 10
          ip link set dev vrf-blue up

  2. An l3mdev FIB rule directs lookups to the table associated with the device.
     A single l3mdev rule is sufficient for all VRFs. The VRF device adds the
     l3mdev rule for IPv4 and IPv6 when the first device is created with a
     default preference of 1000. Users may delete the rule if desired and add
     with a different priority or install per-VRF rules.
  
     Prior to the v4.8 kernel iif and oif rules are needed for each VRF device:

         ip ru add oif vrf-blue table 10
         ip ru add iif vrf-blue table 10

  3. Set the default route for the table (and hence default route for the VRF).
         ip route add table 10 unreachable default

  4. Enslave L3 interfaces to a VRF device.
         ip link set dev eth1 master vrf-blue

  
     Local and connected routes for enslaved devices are automatically moved to
     the table associated with VRF device. Any additional routes depending on

     the enslaved device are dropped and will need to be reinserted to the VRF
     FIB table following the enslavement.
  
     The IPv6 sysctl option keep_addr_on_down can be enabled to keep IPv6 global
     addresses as VRF enslavement changes.
         sysctl -w net.ipv6.conf.all.keep_addr_on_down=1

  5. Additional VRF routes are added to associated table.
         ip route add table 10 ...

  
  
  Applications
  ------------
  Applications that are to work within a VRF need to bind their socket to the
  VRF device:
  
      setsockopt(sd, SOL_SOCKET, SO_BINDTODEVICE, dev, strlen(dev)+1);
  
  or to specify the output device using cmsg and IP_PKTINFO.

  TCP services running in the default VRF context (ie., not bound to any VRF
  device) can work across all VRF domains by enabling the tcp_l3mdev_accept
  sysctl option:
      sysctl -w net.ipv4.tcp_l3mdev_accept=1

  netfilter rules on the VRF device can be used to limit access to services
  running in the default VRF context as well.
  
  The default VRF does not have limited scope with respect to port bindings.
  That is, if a process does a wildcard bind to a port in the default VRF it
  owns the port across all VRF domains within the network namespace.

  
  ################################################################################
  
  Using iproute2 for VRFs
  =======================

  iproute2 supports the vrf keyword as of v4.7. For backwards compatibility this
  section lists both commands where appropriate -- with the vrf keyword and the
  older form without it.

  
  1. Create a VRF
  
     To instantiate a VRF device and associate it with a table:
         $ ip link add dev NAME type vrf table ID

     As of v4.8 the kernel supports the l3mdev FIB rule where a single rule
     covers all VRFs. The l3mdev rule is created for IPv4 and IPv6 on first
     device create.

  
  2. List VRFs
  
     To list VRFs that have been created:
         $ ip [-d] link show type vrf
           NOTE: The -d option is needed to show the table id
  
     For example:
     $ ip -d link show type vrf

     11: mgmt: <NOARP,MASTER,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000

         link/ether 72:b3:ba:91:e2:24 brd ff:ff:ff:ff:ff:ff promiscuity 0
         vrf table 1 addrgenmode eui64

     12: red: <NOARP,MASTER,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000

         link/ether b6:6f:6e:f6:da:73 brd ff:ff:ff:ff:ff:ff promiscuity 0
         vrf table 10 addrgenmode eui64

     13: blue: <NOARP,MASTER,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000

         link/ether 36:62:e8:7d:bb:8c brd ff:ff:ff:ff:ff:ff promiscuity 0
         vrf table 66 addrgenmode eui64

     14: green: <NOARP,MASTER,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000

         link/ether e6:28:b8:63:70:bb brd ff:ff:ff:ff:ff:ff promiscuity 0
         vrf table 81 addrgenmode eui64
  
  
     Or in brief output:
  
     $ ip -br link show type vrf

     mgmt         UP             72:b3:ba:91:e2:24 <NOARP,MASTER,UP,LOWER_UP>
     red          UP             b6:6f:6e:f6:da:73 <NOARP,MASTER,UP,LOWER_UP>
     blue         UP             36:62:e8:7d:bb:8c <NOARP,MASTER,UP,LOWER_UP>
     green        UP             e6:28:b8:63:70:bb <NOARP,MASTER,UP,LOWER_UP>

  
  
  3. Assign a Network Interface to a VRF
  
     Network interfaces are assigned to a VRF by enslaving the netdevice to a
     VRF device:

         $ ip link set dev NAME master NAME

  
     On enslavement connected and local routes are automatically moved to the
     table associated with the VRF device.
  
     For example:

     $ ip link set dev eth0 master mgmt

  
  
  4. Show Devices Assigned to a VRF
  
     To show devices that have been assigned to a specific VRF add the master
     option to the ip command:

         $ ip link show vrf NAME
         $ ip link show master NAME

  
     For example:

     $ ip link show vrf red
     3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master red state UP mode DEFAULT group default qlen 1000

         link/ether 02:00:00:00:02:02 brd ff:ff:ff:ff:ff:ff

     4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master red state UP mode DEFAULT group default qlen 1000

         link/ether 02:00:00:00:02:03 brd ff:ff:ff:ff:ff:ff

     7: eth5: <BROADCAST,MULTICAST> mtu 1500 qdisc noop master red state DOWN mode DEFAULT group default qlen 1000

         link/ether 02:00:00:00:02:06 brd ff:ff:ff:ff:ff:ff
  
  
     Or using the brief output:

     $ ip -br link show vrf red

     eth1             UP             02:00:00:00:02:02 <BROADCAST,MULTICAST,UP,LOWER_UP>
     eth2             UP             02:00:00:00:02:03 <BROADCAST,MULTICAST,UP,LOWER_UP>
     eth5             DOWN           02:00:00:00:02:06 <BROADCAST,MULTICAST>
  
  
  5. Show Neighbor Entries for a VRF
  
     To list neighbor entries associated with devices enslaved to a VRF device
     add the master option to the ip command:

         $ ip [-6] neigh show vrf NAME
         $ ip [-6] neigh show master NAME

  
     For example:

     $  ip neigh show vrf red

     10.2.1.254 dev eth1 lladdr a6:d9:c7:4f:06:23 REACHABLE
     10.2.2.254 dev eth2 lladdr 5e:54:01:6a:ee:80 REACHABLE

     $ ip -6 neigh show vrf red
     2002:1::64 dev eth1 lladdr a6:d9:c7:4f:06:23 REACHABLE

  
  
  6. Show Addresses for a VRF
  
     To show addresses for interfaces associated with a VRF add the master
     option to the ip command:

         $ ip addr show vrf NAME
         $ ip addr show master NAME

  
     For example:

     $ ip addr show vrf red
     3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master red state UP group default qlen 1000

         link/ether 02:00:00:00:02:02 brd ff:ff:ff:ff:ff:ff
         inet 10.2.1.2/24 brd 10.2.1.255 scope global eth1
            valid_lft forever preferred_lft forever
         inet6 2002:1::2/120 scope global
            valid_lft forever preferred_lft forever
         inet6 fe80::ff:fe00:202/64 scope link
            valid_lft forever preferred_lft forever

     4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master red state UP group default qlen 1000

         link/ether 02:00:00:00:02:03 brd ff:ff:ff:ff:ff:ff
         inet 10.2.2.2/24 brd 10.2.2.255 scope global eth2
            valid_lft forever preferred_lft forever
         inet6 2002:2::2/120 scope global
            valid_lft forever preferred_lft forever
         inet6 fe80::ff:fe00:203/64 scope link
            valid_lft forever preferred_lft forever

     7: eth5: <BROADCAST,MULTICAST> mtu 1500 qdisc noop master red state DOWN group default qlen 1000

         link/ether 02:00:00:00:02:06 brd ff:ff:ff:ff:ff:ff
  
     Or in brief format:

     $ ip -br addr show vrf red

     eth1             UP             10.2.1.2/24 2002:1::2/120 fe80::ff:fe00:202/64
     eth2             UP             10.2.2.2/24 2002:2::2/120 fe80::ff:fe00:203/64
     eth5             DOWN
  
  
  7. Show Routes for a VRF
  
     To show routes for a VRF use the ip command to display the table associated
     with the VRF device:

         $ ip [-6] route show vrf NAME

         $ ip [-6] route show table ID
  
     For example:

     $ ip route show vrf red

     prohibit default
     broadcast 10.2.1.0 dev eth1  proto kernel  scope link  src 10.2.1.2
     10.2.1.0/24 dev eth1  proto kernel  scope link  src 10.2.1.2
     local 10.2.1.2 dev eth1  proto kernel  scope host  src 10.2.1.2
     broadcast 10.2.1.255 dev eth1  proto kernel  scope link  src 10.2.1.2
     broadcast 10.2.2.0 dev eth2  proto kernel  scope link  src 10.2.2.2
     10.2.2.0/24 dev eth2  proto kernel  scope link  src 10.2.2.2
     local 10.2.2.2 dev eth2  proto kernel  scope host  src 10.2.2.2
     broadcast 10.2.2.255 dev eth2  proto kernel  scope link  src 10.2.2.2

     $ ip -6 route show vrf red

     local 2002:1:: dev lo  proto none  metric 0  pref medium
     local 2002:1::2 dev lo  proto none  metric 0  pref medium
     2002:1::/120 dev eth1  proto kernel  metric 256  pref medium
     local 2002:2:: dev lo  proto none  metric 0  pref medium
     local 2002:2::2 dev lo  proto none  metric 0  pref medium
     2002:2::/120 dev eth2  proto kernel  metric 256  pref medium
     local fe80:: dev lo  proto none  metric 0  pref medium
     local fe80:: dev lo  proto none  metric 0  pref medium
     local fe80::ff:fe00:202 dev lo  proto none  metric 0  pref medium
     local fe80::ff:fe00:203 dev lo  proto none  metric 0  pref medium
     fe80::/64 dev eth1  proto kernel  metric 256  pref medium
     fe80::/64 dev eth2  proto kernel  metric 256  pref medium

     ff00::/8 dev red  metric 256  pref medium

     ff00::/8 dev eth1  metric 256  pref medium
     ff00::/8 dev eth2  metric 256  pref medium
  
  
  8. Route Lookup for a VRF

     A test route lookup can be done for a VRF:
         $ ip [-6] route get vrf NAME ADDRESS
         $ ip [-6] route get oif NAME ADDRESS

  
     For example:

     $ ip route get 10.2.1.40 vrf red
     10.2.1.40 dev eth1  table red  src 10.2.1.2

         cache

     $ ip -6 route get 2002:1::32 vrf red
     2002:1::32 from :: dev eth1  table red  proto kernel  src 2002:1::2  metric 256  pref medium

  
  
  9. Removing Network Interface from a VRF
  
     Network interfaces are removed from a VRF by breaking the enslavement to
     the VRF device:
         $ ip link set dev NAME nomaster
  
     Connected routes are moved back to the default table and local entries are
     moved to the local table.
  
     For example:
     $ ip link set dev eth0 nomaster
  
  --------------------------------------------------------------------------------
  
  Commands used in this example:

  cat >> /etc/iproute2/rt_tables.d/vrf.conf <<EOF
  1  mgmt
  10 red
  66 blue
  81 green

  EOF
  
  function vrf_create
  {
      VRF=$1
      TBID=$2

      # create VRF device
      ip link add ${VRF} type vrf table ${TBID}

  
      if [ "${VRF}" != "mgmt" ]; then

          ip route add table ${TBID} unreachable default

      fi

      ip link set dev ${VRF} up

  }
  
  vrf_create mgmt 1

  ip link set dev eth0 master mgmt

  
  vrf_create red 10

  ip link set dev eth1 master red
  ip link set dev eth2 master red
  ip link set dev eth5 master red

  
  vrf_create blue 66

  ip link set dev eth3 master blue

  
  vrf_create green 81

  ip link set dev eth4 master green

  
  
  Interface addresses from /etc/network/interfaces:
  auto eth0
  iface eth0 inet static
        address 10.0.0.2
        netmask 255.255.255.0
        gateway 10.0.0.254
  
  iface eth0 inet6 static
        address 2000:1::2
        netmask 120
  
  auto eth1
  iface eth1 inet static
        address 10.2.1.2
        netmask 255.255.255.0
  
  iface eth1 inet6 static
        address 2002:1::2
        netmask 120
  
  auto eth2
  iface eth2 inet static
        address 10.2.2.2
        netmask 255.255.255.0
  
  iface eth2 inet6 static
        address 2002:2::2
        netmask 120
  
  auto eth3
  iface eth3 inet static
        address 10.2.3.2
        netmask 255.255.255.0
  
  iface eth3 inet6 static
        address 2002:3::2
        netmask 120
  
  auto eth4
  iface eth4 inet static
        address 10.2.4.2
        netmask 255.255.255.0
  
  iface eth4 inet6 static
        address 2002:4::2
        netmask 120