mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-26 02:39:48 +00:00
![Benjamin Poirier](/assets/img/avatar_default.png)
As suggested by David, document a somewhat unexpected behavior that results from net.ipv4.tcp_l3mdev_accept=1. This behavior was encountered while debugging FRR, a VRF-aware application, on a system which used net.ipv4.tcp_l3mdev_accept=1 and where TCP connections for BGP with MD5 keys were failing to establish. Cc: David Ahern <dsahern@gmail.com> Signed-off-by: Benjamin Poirier <bpoirier@nvidia.com> Reviewed-by: David Ahern <dsahern@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
464 lines
16 KiB
ReStructuredText
464 lines
16 KiB
ReStructuredText
.. 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
|