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net: vrf: Documentation update
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Update vrf documentation for changes made to 4.4 - 4.8 kernels
and iproute2 support for vrf keyword.

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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David Ahern authored and David S. Miller committed Jul 13, 2016
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Showing 1 changed file with 103 additions and 98 deletions.
201 changes: 103 additions & 98 deletions Documentation/networking/vrf.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -15,9 +15,9 @@ 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.
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
------
Expand All @@ -37,45 +37,56 @@ are then enslaved to a VRF device:
+------+ +------+

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.
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 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.

[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. Rules are added that send lookups to the associated FIB table when the
iif or oif is the VRF device. e.g.,
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

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

3. Enslave L3 interfaces to a VRF device.
e.g, ip link set dev eth1 master vrf-blue
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 will need to be reinserted following the enslavement.
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

4. Additional VRF routes are added to associated table.
e.g., ip route add table 10 ...
5. Additional VRF routes are added to associated table.
ip route add table 10 ...


Applications
Expand All @@ -87,39 +98,34 @@ VRF device:

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

Limitations
-----------
Index of original ingress interface is not available via cmsg. Will address
soon.
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
=======================
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.
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

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

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

Expand All @@ -129,60 +135,61 @@ for emphasis of the device type, similar to use of 'br' in bridge names.

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
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: vrf-red: <NOARP,MASTER,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
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: vrf-blue: <NOARP,MASTER,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
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: vrf-green: <NOARP,MASTER,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
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
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>
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 VRF-NAME
$ 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 vrf-mgmt
$ 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 master VRF-NAME
$ ip link show vrf NAME
$ ip link show master 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
$ 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 vrf-red state UP mode DEFAULT group default qlen 1000
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 vrf-red state DOWN mode DEFAULT group default qlen 1000
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 master vrf-red
$ ip -br link show master 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>
Expand All @@ -192,46 +199,48 @@ for emphasis of the device type, similar to use of 'br' in bridge names.

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

For example:
$ ip neigh show master vrf-red
$ 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 master vrf-red
$ 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 master VRF-NAME
$ ip addr show vrf NAME
$ ip addr show master 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
$ 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 vrf-red state UP group default qlen 1000
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 vrf-red state DOWN group default qlen 1000
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 master vrf-red
$ 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
Expand All @@ -241,10 +250,11 @@ for emphasis of the device type, similar to use of 'br' in bridge names.

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 table vrf-red
$ 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
Expand All @@ -255,7 +265,7 @@ for emphasis of the device type, similar to use of 'br' in bridge names.
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
$ 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
Expand All @@ -268,23 +278,24 @@ for emphasis of the device type, similar to use of 'br' in bridge names.
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 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
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 oif vrf-red
10.2.1.40 dev eth1 table vrf-red src 10.2.1.2
$ 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 oif vrf-red
2002:1::32 from :: dev eth1 table vrf-red proto kernel src 2002:1::2 metric 256 pref medium
$ 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
Expand All @@ -303,46 +314,40 @@ for emphasis of the device type, similar to use of 'br' in bridge names.

Commands used in this example:

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

function vrf_create
{
VRF=$1
TBID=$2
# create VRF device
ip link add vrf-${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}
# create VRF device
ip link add ${VRF} type vrf table ${TBID}

if [ "${VRF}" != "mgmt" ]; then
ip route add table ${TBID} prohibit default
ip route add table ${TBID} unreachable default
fi
ip link set dev vrf-${VRF} up
ip link set dev vrf-${VRF} state up
ip link set dev ${VRF} up
}

vrf_create mgmt 1
ip link set dev eth0 master vrf-mgmt
ip link set dev eth0 master 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
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 vrf-blue
ip link set dev eth3 master blue

vrf_create green 81
ip link set dev eth4 master vrf-green
ip link set dev eth4 master green


Interface addresses from /etc/network/interfaces:
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