399 lines
14 KiB
Plaintext
399 lines
14 KiB
Plaintext
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Virtual Routing and Forwarding (VRF)
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====================================
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The VRF device combined with ip rules provides the ability to create virtual
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routing and forwarding domains (aka VRFs, VRF-lite to be specific) in the
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Linux network stack. One use case is the multi-tenancy problem where each
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tenant has their own unique routing tables and in the very least need
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different default gateways.
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Processes can be "VRF aware" by binding a socket to the VRF device. Packets
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through the socket then use the routing table associated with the VRF
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device. An important feature of the VRF device implementation is that it
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impacts only Layer 3 and above so L2 tools (e.g., LLDP) are not affected
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(ie., they do not need to be run in each VRF). The design also allows
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the use of higher priority ip rules (Policy Based Routing, PBR) to take
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precedence over the VRF device rules directing specific traffic as desired.
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In addition, VRF devices allow VRFs to be nested within namespaces. For
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example network namespaces provide separation of network interfaces at the
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device layer, VLANs on the interfaces within a namespace provide L2 separation
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and then VRF devices provide L3 separation.
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Design
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------
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A VRF device is created with an associated route table. Network interfaces
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are then enslaved to a VRF device:
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+-----------------------------+
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| vrf-blue | ===> route table 10
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+-----------------------------+
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| | |
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+------+ +------+ +-------------+
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| eth1 | | eth2 | ... | bond1 |
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+------+ +------+ +-------------+
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| |
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+------+ +------+
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| eth8 | | eth9 |
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+------+ +------+
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Packets received on an enslaved device and are switched to the VRF device
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in the IPv4 and IPv6 processing stacks giving the impression that packets
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flow through the VRF device. Similarly on egress routing rules are used to
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send packets to the VRF device driver before getting sent out the actual
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interface. This allows tcpdump on a VRF device to capture all packets into
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and out of the VRF as a whole.[1] Similarly, netfilter[2] and tc rules can be
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applied using the VRF device to specify rules that apply to the VRF domain
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as a whole.
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[1] Packets in the forwarded state do not flow through the device, so those
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packets are not seen by tcpdump. Will revisit this limitation in a
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future release.
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[2] Iptables on ingress supports PREROUTING with skb->dev set to the real
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ingress device and both INPUT and PREROUTING rules with skb->dev set to
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the VRF device. For egress POSTROUTING and OUTPUT rules can be written
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using either the VRF device or real egress device.
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Setup
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-----
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1. VRF device is created with an association to a FIB table.
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e.g, ip link add vrf-blue type vrf table 10
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ip link set dev vrf-blue up
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2. An l3mdev FIB rule directs lookups to the table associated with the device.
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A single l3mdev rule is sufficient for all VRFs. The VRF device adds the
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l3mdev rule for IPv4 and IPv6 when the first device is created with a
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default preference of 1000. Users may delete the rule if desired and add
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with a different priority or install per-VRF rules.
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Prior to the v4.8 kernel iif and oif rules are needed for each VRF device:
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ip ru add oif vrf-blue table 10
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ip ru add iif vrf-blue table 10
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3. Set the default route for the table (and hence default route for the VRF).
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ip route add table 10 unreachable default
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4. Enslave L3 interfaces to a VRF device.
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ip link set dev eth1 master vrf-blue
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Local and connected routes for enslaved devices are automatically moved to
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the table associated with VRF device. Any additional routes depending on
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the enslaved device are dropped and will need to be reinserted to the VRF
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FIB table following the enslavement.
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The IPv6 sysctl option keep_addr_on_down can be enabled to keep IPv6 global
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addresses as VRF enslavement changes.
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sysctl -w net.ipv6.conf.all.keep_addr_on_down=1
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5. Additional VRF routes are added to associated table.
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ip route add table 10 ...
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Applications
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------------
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Applications that are to work within a VRF need to bind their socket to the
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VRF device:
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setsockopt(sd, SOL_SOCKET, SO_BINDTODEVICE, dev, strlen(dev)+1);
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or to specify the output device using cmsg and IP_PKTINFO.
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TCP services running in the default VRF context (ie., not bound to any VRF
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device) can work across all VRF domains by enabling the tcp_l3mdev_accept
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sysctl option:
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sysctl -w net.ipv4.tcp_l3mdev_accept=1
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netfilter rules on the VRF device can be used to limit access to services
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running in the default VRF context as well.
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The default VRF does not have limited scope with respect to port bindings.
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That is, if a process does a wildcard bind to a port in the default VRF it
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owns the port across all VRF domains within the network namespace.
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################################################################################
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Using iproute2 for VRFs
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=======================
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iproute2 supports the vrf keyword as of v4.7. For backwards compatibility this
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section lists both commands where appropriate -- with the vrf keyword and the
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older form without it.
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1. Create a VRF
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To instantiate a VRF device and associate it with a table:
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$ ip link add dev NAME type vrf table ID
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As of v4.8 the kernel supports the l3mdev FIB rule where a single rule
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covers all VRFs. The l3mdev rule is created for IPv4 and IPv6 on first
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device create.
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2. List VRFs
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To list VRFs that have been created:
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$ ip [-d] link show type vrf
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NOTE: The -d option is needed to show the table id
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For example:
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$ ip -d link show type vrf
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11: mgmt: <NOARP,MASTER,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
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link/ether 72:b3:ba:91:e2:24 brd ff:ff:ff:ff:ff:ff promiscuity 0
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vrf table 1 addrgenmode eui64
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12: red: <NOARP,MASTER,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
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link/ether b6:6f:6e:f6:da:73 brd ff:ff:ff:ff:ff:ff promiscuity 0
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vrf table 10 addrgenmode eui64
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13: blue: <NOARP,MASTER,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
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link/ether 36:62:e8:7d:bb:8c brd ff:ff:ff:ff:ff:ff promiscuity 0
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vrf table 66 addrgenmode eui64
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14: green: <NOARP,MASTER,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
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link/ether e6:28:b8:63:70:bb brd ff:ff:ff:ff:ff:ff promiscuity 0
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vrf table 81 addrgenmode eui64
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Or in brief output:
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$ ip -br link show type vrf
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mgmt UP 72:b3:ba:91:e2:24 <NOARP,MASTER,UP,LOWER_UP>
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red UP b6:6f:6e:f6:da:73 <NOARP,MASTER,UP,LOWER_UP>
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blue UP 36:62:e8:7d:bb:8c <NOARP,MASTER,UP,LOWER_UP>
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green UP e6:28:b8:63:70:bb <NOARP,MASTER,UP,LOWER_UP>
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3. Assign a Network Interface to a VRF
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Network interfaces are assigned to a VRF by enslaving the netdevice to a
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VRF device:
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$ ip link set dev NAME master NAME
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On enslavement connected and local routes are automatically moved to the
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table associated with the VRF device.
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For example:
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$ ip link set dev eth0 master mgmt
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4. Show Devices Assigned to a VRF
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To show devices that have been assigned to a specific VRF add the master
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option to the ip command:
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$ ip link show vrf NAME
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$ ip link show master NAME
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For example:
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$ ip link show vrf red
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3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master red state UP mode DEFAULT group default qlen 1000
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link/ether 02:00:00:00:02:02 brd ff:ff:ff:ff:ff:ff
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4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master red state UP mode DEFAULT group default qlen 1000
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link/ether 02:00:00:00:02:03 brd ff:ff:ff:ff:ff:ff
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7: eth5: <BROADCAST,MULTICAST> mtu 1500 qdisc noop master red state DOWN mode DEFAULT group default qlen 1000
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link/ether 02:00:00:00:02:06 brd ff:ff:ff:ff:ff:ff
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Or using the brief output:
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$ ip -br link show vrf red
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eth1 UP 02:00:00:00:02:02 <BROADCAST,MULTICAST,UP,LOWER_UP>
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eth2 UP 02:00:00:00:02:03 <BROADCAST,MULTICAST,UP,LOWER_UP>
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eth5 DOWN 02:00:00:00:02:06 <BROADCAST,MULTICAST>
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5. Show Neighbor Entries for a VRF
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To list neighbor entries associated with devices enslaved to a VRF device
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add the master option to the ip command:
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$ ip [-6] neigh show vrf NAME
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$ ip [-6] neigh show master NAME
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For example:
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$ ip neigh show vrf red
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10.2.1.254 dev eth1 lladdr a6:d9:c7:4f:06:23 REACHABLE
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10.2.2.254 dev eth2 lladdr 5e:54:01:6a:ee:80 REACHABLE
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$ ip -6 neigh show vrf red
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2002:1::64 dev eth1 lladdr a6:d9:c7:4f:06:23 REACHABLE
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6. Show Addresses for a VRF
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To show addresses for interfaces associated with a VRF add the master
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option to the ip command:
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$ ip addr show vrf NAME
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$ ip addr show master NAME
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For example:
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$ ip addr show vrf red
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3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master red state UP group default qlen 1000
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link/ether 02:00:00:00:02:02 brd ff:ff:ff:ff:ff:ff
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inet 10.2.1.2/24 brd 10.2.1.255 scope global eth1
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valid_lft forever preferred_lft forever
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inet6 2002:1::2/120 scope global
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valid_lft forever preferred_lft forever
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inet6 fe80::ff:fe00:202/64 scope link
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valid_lft forever preferred_lft forever
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4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master red state UP group default qlen 1000
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link/ether 02:00:00:00:02:03 brd ff:ff:ff:ff:ff:ff
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inet 10.2.2.2/24 brd 10.2.2.255 scope global eth2
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valid_lft forever preferred_lft forever
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inet6 2002:2::2/120 scope global
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valid_lft forever preferred_lft forever
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inet6 fe80::ff:fe00:203/64 scope link
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valid_lft forever preferred_lft forever
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7: eth5: <BROADCAST,MULTICAST> mtu 1500 qdisc noop master red state DOWN group default qlen 1000
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link/ether 02:00:00:00:02:06 brd ff:ff:ff:ff:ff:ff
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Or in brief format:
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$ ip -br addr show vrf red
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eth1 UP 10.2.1.2/24 2002:1::2/120 fe80::ff:fe00:202/64
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eth2 UP 10.2.2.2/24 2002:2::2/120 fe80::ff:fe00:203/64
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eth5 DOWN
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7. Show Routes for a VRF
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To show routes for a VRF use the ip command to display the table associated
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with the VRF device:
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$ ip [-6] route show vrf NAME
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$ ip [-6] route show table ID
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For example:
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$ ip route show vrf red
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prohibit default
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broadcast 10.2.1.0 dev eth1 proto kernel scope link src 10.2.1.2
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10.2.1.0/24 dev eth1 proto kernel scope link src 10.2.1.2
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local 10.2.1.2 dev eth1 proto kernel scope host src 10.2.1.2
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broadcast 10.2.1.255 dev eth1 proto kernel scope link src 10.2.1.2
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broadcast 10.2.2.0 dev eth2 proto kernel scope link src 10.2.2.2
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10.2.2.0/24 dev eth2 proto kernel scope link src 10.2.2.2
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local 10.2.2.2 dev eth2 proto kernel scope host src 10.2.2.2
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broadcast 10.2.2.255 dev eth2 proto kernel scope link src 10.2.2.2
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$ ip -6 route show vrf red
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local 2002:1:: dev lo proto none metric 0 pref medium
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local 2002:1::2 dev lo proto none metric 0 pref medium
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2002:1::/120 dev eth1 proto kernel metric 256 pref medium
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local 2002:2:: dev lo proto none metric 0 pref medium
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local 2002:2::2 dev lo proto none metric 0 pref medium
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2002:2::/120 dev eth2 proto kernel metric 256 pref medium
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local fe80:: dev lo proto none metric 0 pref medium
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local fe80:: dev lo proto none metric 0 pref medium
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local fe80::ff:fe00:202 dev lo proto none metric 0 pref medium
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local fe80::ff:fe00:203 dev lo proto none metric 0 pref medium
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fe80::/64 dev eth1 proto kernel metric 256 pref medium
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fe80::/64 dev eth2 proto kernel metric 256 pref medium
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ff00::/8 dev red metric 256 pref medium
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ff00::/8 dev eth1 metric 256 pref medium
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ff00::/8 dev eth2 metric 256 pref medium
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8. Route Lookup for a VRF
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A test route lookup can be done for a VRF:
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$ ip [-6] route get vrf NAME ADDRESS
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$ ip [-6] route get oif NAME ADDRESS
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For example:
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$ ip route get 10.2.1.40 vrf red
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10.2.1.40 dev eth1 table red src 10.2.1.2
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cache
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$ ip -6 route get 2002:1::32 vrf red
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2002:1::32 from :: dev eth1 table red proto kernel src 2002:1::2 metric 256 pref medium
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9. Removing Network Interface from a VRF
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Network interfaces are removed from a VRF by breaking the enslavement to
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the VRF device:
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$ ip link set dev NAME nomaster
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Connected routes are moved back to the default table and local entries are
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moved to the local table.
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For example:
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$ ip link set dev eth0 nomaster
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--------------------------------------------------------------------------------
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Commands used in this example:
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cat >> /etc/iproute2/rt_tables.d/vrf.conf <<EOF
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1 mgmt
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10 red
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66 blue
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81 green
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EOF
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function vrf_create
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{
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VRF=$1
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TBID=$2
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# create VRF device
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ip link add ${VRF} type vrf table ${TBID}
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if [ "${VRF}" != "mgmt" ]; then
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ip route add table ${TBID} unreachable default
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fi
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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
|