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+.. SPDX-License-Identifier: GPL-2.0
+
+====================================
+Virtual Routing and Forwarding (VRF)
+====================================
+
+The VRF Device
+==============
+
+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 metric 4278198272
+
+ This high metric value ensures that the default unreachable route can
+ be overridden by a routing protocol suite. FRRouting interprets
+ kernel metrics as a combined admin distance (upper byte) and priority
+ (lower 3 bytes). Thus the above metric translates to [255/8192].
+
+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.
+
+By default the scope of the port bindings for unbound sockets is
+limited to the default VRF. That is, it will not be matched by packets
+arriving on interfaces enslaved to an l3mdev and processes may bind to
+the same port if they bind to an l3mdev.
+
+TCP & UDP 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 and udp_l3mdev_accept sysctl options::
+
+ sysctl -w net.ipv4.tcp_l3mdev_accept=1
+ sysctl -w net.ipv4.udp_l3mdev_accept=1
+
+These options are disabled by default so that a socket in a VRF is only
+selected for packets in that VRF. There is a similar option for RAW
+sockets, which is enabled by default for reasons of backwards compatibility.
+This is so as to specify the output device with cmsg and IP_PKTINFO, but
+using a socket not bound to the corresponding VRF. This allows e.g. older ping
+implementations to be run with specifying the device but without executing it
+in the VRF. This option can be disabled so that packets received in a VRF
+context are only handled by a raw socket bound to the VRF, and packets in the
+default VRF are only handled by a socket not bound to any VRF::
+
+ sysctl -w net.ipv4.raw_l3mdev_accept=0
+
+netfilter rules on the VRF device can be used to limit access to services
+running in the default VRF context as well.
+
+Using VRF-aware applications (applications which simultaneously create sockets
+outside and inside VRFs) in conjunction with ``net.ipv4.tcp_l3mdev_accept=1``
+is possible but may lead to problems in some situations. With that sysctl
+value, it is unspecified which listening socket will be selected to handle
+connections for VRF traffic; ie. either a socket bound to the VRF or an unbound
+socket may be used to accept new connections from a VRF. This somewhat
+unexpected behavior can lead to problems if sockets are configured with extra
+options (ex. TCP MD5 keys) with the expectation that VRF traffic will
+exclusively be handled by sockets bound to VRFs, as would be the case with
+``net.ipv4.tcp_l3mdev_accept=0``. Finally and as a reminder, regardless of
+which listening socket is selected, established sockets will be created in the
+VRF based on the ingress interface, as documented earlier.
+
+--------------------------------------------------------------------------------
+
+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
+ unreachable default metric 4278198272
+ 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
+ unreachable default dev lo metric 4278198272 error -101 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 metric 4278198272
+ 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
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-03 06:55:05 +0000