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Diffstat (limited to 'Documentation/networking/vrf.txt')
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diff --git a/Documentation/networking/vrf.txt b/Documentation/networking/vrf.txt new file mode 100644 index 000000000000..031ef4a63485 --- /dev/null +++ b/Documentation/networking/vrf.txt @@ -0,0 +1,96 @@ +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] Similiarly, 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 +----------- +VRF device currently only works for IPv4. Support for IPv6 is under development. + +Index of original ingress interface is not available via cmsg. Will address +soon. |