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 L1
(Layer 1 separation), 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
using an rx_handler which gives 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 is limited to NF_INET_PRE_ROUTING only with skb->dev
set to real ingress device and egress is limited to NF_INET_POST_ROUTING.
Will revisit this limitation in a future release.
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. Rules are added that send lookups to the associated FIB table when the
iif or oif is the VRF device. e.g.,
ip ru add oif vrf-blue table 10
ip ru add iif vrf-blue table 10
Set the default route for the table (and hence default route for the VRF).
e.g, ip route add table 10 prohibit default
3. Enslave L3 interfaces to a VRF device.
e.g, 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 will need to be reinserted following the enslavement.
4. Additional VRF routes are added to associated table.
e.g., 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.
Limitations
-----------
Index of original ingress interface is not available via cmsg. Will address
soon.
################################################################################
Using iproute2 for VRFs
=======================
VRF devices do *not* have to start with 'vrf-'. That is a convention used here
for emphasis of the device type, similar to use of 'br' in bridge names.
1. Create a VRF
To instantiate a VRF device and associate it with a table:
$ ip link add dev NAME type vrf table ID
Remember to add the ip rules as well:
$ ip ru add oif NAME table 10
$ ip ru add iif NAME table 10
$ ip -6 ru add oif NAME table 10
$ ip -6 ru add iif NAME table 10
Without the rules route lookups are not directed to the table.
For example:
$ ip link add dev vrf-blue type vrf table 10
$ ip ru add pref 200 oif vrf-blue table 10
$ ip ru add pref 200 iif vrf-blue table 10
$ ip -6 ru add pref 200 oif vrf-blue table 10
$ ip -6 ru add pref 200 iif vrf-blue table 10
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: vrf-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: vrf-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: vrf-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: vrf-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
vrf-mgmt UP 72:b3:ba:91:e2:24 <NOARP,MASTER,UP,LOWER_UP>
vrf-red UP b6:6f:6e:f6:da:73 <NOARP,MASTER,UP,LOWER_UP>
vrf-blue UP 36:62:e8:7d:bb:8c <NOARP,MASTER,UP,LOWER_UP>
vrf-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 VRF-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 vrf-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 master VRF-NAME
For example:
$ ip link show master vrf-red
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master vrf-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 vrf-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 vrf-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 master 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 master VRF-NAME
For example:
$ ip neigh show master 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 master 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 master VRF-NAME
For example:
$ ip addr show master vrf-red
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master vrf-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 vrf-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 vrf-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 master 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 table ID
For example:
$ ip route show table 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 table 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 vrf-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 by adding the oif option to ip:
$ ip [-6] route get oif VRF-NAME ADDRESS
For example:
$ ip route get 10.2.1.40 oif vrf-red
10.2.1.40 dev eth1 table vrf-red src 10.2.1.2
cache
$ ip -6 route get 2002:1::32 oif vrf-red
2002:1::32 from :: dev eth1 table vrf-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 <<EOF
1 vrf-mgmt
10 vrf-red
66 vrf-blue
81 vrf-green
EOF
function vrf_create
{
VRF=$1
TBID=$2
# create VRF device
ip link add vrf-${VRF} type vrf table ${TBID}
# add rules that direct lookups to vrf table
ip ru add pref 200 oif vrf-${VRF} table ${TBID}
ip ru add pref 200 iif vrf-${VRF} table ${TBID}
ip -6 ru add pref 200 oif vrf-${VRF} table ${TBID}
ip -6 ru add pref 200 iif vrf-${VRF} table ${TBID}
if [ "${VRF}" != "mgmt" ]; then
ip route add table ${TBID} prohibit default
fi
ip link set dev vrf-${VRF} up
ip link set dev vrf-${VRF} state up
}
vrf_create mgmt 1
ip link set dev eth0 master vrf-mgmt
vrf_create red 10
ip link set dev eth1 master vrf-red
ip link set dev eth2 master vrf-red
ip link set dev eth5 master vrf-red
vrf_create blue 66
ip link set dev eth3 master vrf-blue
vrf_create green 81
ip link set dev eth4 master vrf-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
