In the context of internet scale routing a requirement that always comes
up is the need to partition the available routing tables into disjoint
routing planes. A specific 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.
This patch allows the ability to create virtual router domains (aka VRFs
(VRF-lite to be specific) in the linux packet forwarding stack. The main
observation is that through the use of rules and socket binding to interfaces,
all the facilities that we need are already present in the infrastructure. What
is missing is a handle that identifies a routing domain and can be used to
gather applicable rules/tables and uniqify neighbor selection. The scheme used
needs to preserves the notions of ECMP, and general routing principles.
This driver is a cross between functionality that the IPVLAN driver
and the Team drivers provide where a device is created and packets
into/out of the routing domain are shuttled through this device. The
device is then used as a handle to identify the applicable rules. The
VRF device is thus the layer3 equivalent of a vlan device.
The very important point to note is that this is only a Layer3 concept
so L2 tools (e.g., LLDP) do not need to be run in each VRF, processes can
run in unaware mode or select a VRF to be talking through. Also the
behavioral model is a generalized application of the familiar VRF-Lite
model with some performance paths that need optimization. (Specifically
the output route selector that Roopa, Robert, Thomas and EricB are
currently discussing on the MPLS thread)
High Level points
=
1. Simple overlay driver (minimal changes to current stack)
* uses the existing fib tables and fib rules infrastructure
2. Modelled closely after the ipvlan driver
3. Uses current API and infrastructure.
* Applications can use SO_BINDTODEVICE or cmsg device indentifiers
to pick VRF (ping, traceroute just work)
* Standard IP Rules work, and since they are aggregated against the
device, scale is manageable
4. Completely orthogonal to Namespaces and only provides separation in
the routing plane (and ARP)
N2
N1 (all configs here) +---+
+--+ | |
|swp1 :10.0.1.1+--+swp1 :10.0.1.2 |
| | | |
|swp2 :10.0.2.1+--+swp2 :10.0.2.2 |
| | +---+
| VRF 1|
| table 5 |
| |
+---+
| |
| VRF 2| N3
| table 6 | +---+
| | | |
|swp3 :10.0.2.1+--+swp1 :10.0.2.2 |
| | | |
|swp4 :10.0.3.1+--+swp2 :10.0.3.2 |
+--+ +---+
Given the topology above, the setup needed to get the basic VRF
functions working would be
Create the VRF devices and associate with a table
ip link add vrf1 type vrf table 5
ip link add vrf2 type vrf table 6
Install the lookup rules that map table to VRF domain
ip rule add pref 200 oif vrf1 lookup 5
ip rule add pref 200 iif vrf1 lookup 5
ip rule add pref 200 oif vrf2 lookup 6
ip rule add pref 200 iif vrf2 lookup 6
ip link set vrf1 up
ip link set vrf2 up
Enslave the routing member interfaces
ip link set swp1 master vrf1
ip link set swp2 master vrf1
ip link set swp3 master vrf2
ip link set swp4 master vrf2
Connected and local routes are automatically moved from main and local
tables to the VRF table.
ping using VRF0 is simply
ping -I vrf0 10.0.1.2
Design Highlights
=
If a device is enslaved to a VRF device (ie., associated with a VRF)
then:
1. Rx path
The master device index is used as the iif for all lookups.
2. Tx path
Similarly, for Tx the VRF device oif is used in the flow to direct
lookups to the table associated with the VRF via its rule. From there
the FLOWI_FLAG_VRFSRC flag is used to indicate that the oif should
not be used for FIB table lookups.
3. Connected and local routes
On link up for a device, connected and local routes are added to the
table associated with the VRF device, rather than the local and main
tables.
4. Socket lookups
Sockets operating in the VRF must be bound to the VRF device. As such
socket lookups compare the VRF device index to sk_bound_dev_if.
5. Neighbor entries
Neighbor entries are not impacted by the VRF device. Entries are
associated with a particular interface; the VRF association is indirect
via the interface-to-VRF device enslavement.
Version 6
- addressed
