Configuring VRFs

This document describes the device data model parameters one should consider when creating a VRF configuration template. For a wider picture, please see New Configuration Features for an Existing Device or Contributing New Devices.

This document assumes you’re using an Ansible task list that is able to deploy device configuration from a template. If you plan to use Ansible modules to build device configuration, you’ll find some guidance in Using Ansible Configuration Modules section of OSPF implementation guide.

Notes:

  • The device configuration template (in Jinja2 format) should be stored in netsim/templates/vrf/<nos>.j2 with nos being the value of netlab_device_type or ansible_network_os variable (see Using Your Devices with Ansible Playbooks for more details.

  • Most of the data model attributes are optional. Use if sth is defined, sth|default(value) or if 'sth' in ifdata in your Jinja2 templates to check for presence of optional attributes. Try to be consistent ;)

Data Model

VRFs used on a device are defined in the vrfs dictionary. Dictionary keys are VRF names, dictionary values are dictionaries of VRF parameters which can contain these elements:

  • rd – VRF route distinguisher

  • import – list of import route targets

  • export – list of export route targets

  • af – list of address families (ipv4 and/or ipv6) used by the VRF

  • ospf – VRF OSPF parameters (when there’s an OSPF routing process running in the VRF)

  • bgp – VRF BGP parameters (when the VRF contains at least one CE router running BGP)

Other parameters:

  • VRF interfaces have vrf interface parameter that contains VRF name.

  • OSPF parameters within the vrfs.vrf-name.ospf dictionary are identical to global OSPF parameters

  • BGP parameters within the vrfs.vrf-name.bgp dictionary are identical to global BGP parameters. You will need to focus on networks (networks to be announced in per-VRF BGP AF) and neighbors (BGP sessions with CE routers)

Device Features

The only configurable VRF-related feature is the name of in-VRF loopback interface – you can specify it in devices.<device>.loopback_interface_name. Use ifindex variable to create unique loopback interfaces (ifindex will be set to VRF index when creating VRF loopback interfaces).

Cisco IOS example:

devices:
  iosv:
    loopback_interface_name: Loopback{ifindex}

VRF Configuration Principles

Many network devices lose interface IP addresses when you configure a VRF on the interface. Interface VRF membership should therefore be configured before interface IP addresses – in the initial phase of device configuration.

In most cases, you have to create VRFs before you can use them in interface configuration. The best way to configure VRFs is thus:

  • Create VRFs in netsim/templates/initial/<nos>.vrf.j2 template.

  • Invoke that template in netsim/templates/initial/<nos>.j2 template whenever the device data contains vrfs dictionary.

  • Configure interface VRF membership as part of the standard interface configuration

  • Configure other VRF features (OSPF, BGP) in netsim/templates/vrf/<nos>.j2 template

Create VRFs

In the create VRF template (stored in netsim/templates/initial/<nos>.vrf.j2) iterate over the vrfs dictionary and configure VRFs.

Cisco IOS configures most VRF parameters (RD, RT) in the VRF definition, and uses address families within VRF definition to enable IPv6 and/or IPv6 in the VRF:

{% for vname,vdata in vrfs.items() %}
vrf definition {{ vname }}
 rd {{ vdata.rd }}
{%   for rt in vdata.import %}
 route-target import {{ rt }}
{%   endfor %}
{%   for rt in vdata.export %}
 route-target export {{ rt }}
{%   endfor %}
!
{%   for af in ['ipv4','ipv6'] if af in vdata.af %}
 address-family {{ af }}
 exit-address-family
!
{%   endfor %}
{% endfor %}

Arista EOS defines RD in the VRF definition (route targets are defined in the BGP routing process). It also requires ip routing enabled for individual VRFs:

{% for vname,vdata in vrfs.items() %}
vrf instance {{ vname }}
 rd {{ vdata.rd }}
!
{% if 'ipv4' in vdata.af %}
ip routing vrf {{ vname }}
!
{% endif %}
{% if 'ipv6' in vdata.af %}
ipv6 routing vrf {{ vname }}
!
{% endif %}
{% endfor %}

Include the VRF creation template in netsim/templates/initial/<nos>.j2 template:

{% if vrfs is defined %}
{% include '<nos>.vrf.j2' %}
{% endif %}

Finally, put interfaces into VRFs based on vrf interface parameter within the interface configuration part of netsim/templates/initial/<nos>.j2. For example:

{% for l in interfaces|default([]) %}
interface {{ l.ifname }}
 no shutdown
{% if l.vrf is defined %}
 vrf forwarding {{ l.vrf }}
{% endif %}
...
{% endfor +%}

Configuring Other VRF Features

Depending on the VRF-aware routing protocols supported by your platform you might have to configure per-VRF OSPF routing processes or VRF BGP address families.

You can configure all of these features in netsim/templates/vrf/<nos>.j2 template, or use a more structured approach:

  • Configure per-VRF OSPF routing process in netsim/templates/vrf/<nos>.ospfv2.j2 and/or netsim/templates/vrf/<nos>.ospfv3.j2

  • Configure VRF BGP address families in netsim/templates/vrf/<nos>.bgp.j2

  • Include these templates in netsim/templates/vrf/<nos>.j2 template based on presence of bgp.as attribute (the device is running BGP) or ospf attribute of a VRF dictionary (VRF is running OSPF)

Cisco IOS example:

{% if bgp.as is defined %}
{% include 'ios.bgp.j2' %}
{% endif %}
{% for vname,vdata in vrfs.items() if 'ospf' in vdata %}
{%   include 'ios.ospfv2-vrf.j2' %}
{% endfor %}

Configuring BGP

In the BGP configuration process, configure VRF address families, OSPF-to-BGP redistribution, redistribution of connected interfaces, and advertise VRF-specific networks.

Cisco IOS has different address families for IPv4-in-VRF and IPv6-in-VRF.

{% import "ios.bgp-macro.j2" as bgpcfg %}
!
router bgp {{ bgp.as }}
{% for vname,vdata in vrfs.items() %}
{%   for af in ('ipv4','ipv6') if af in vdata.af %}
 address-family {{ af }} vrf {{ vname }}
  redistribute connected
{%     if af == 'ipv4' and 'ospf' in vdata %}
  redistribute ospf {{ vdata.vrfidx }}
{%     endif %}
!
{%     for n in vdata.networks|default([]) if af in n %}
{{       bgpcfg.bgp_network(af,n[af]) }}
{%     endfor %}
!
... BGP neighbors ...
{% endfor %}

Note: Cisco IOS template uses a macro to configure BGP network advertisement. See Configure BGP Neighbors for more details.

Arista EOS has VRF BGP configuration mode where you specify both IPv4 and IPv6 route targets. You have to enable individual address families within that configuration mode:

mpls ip
!
router bgp {{ bgp.as }}
{% for vname,vdata in vrfs.items() %}
!
 vrf {{ vname }}
  redistribute connected
  router-id {{ bgp.router_id }}
  rd {{ vdata.rd }}
{%   if 'ospf' in vdata %}
  redistribute ospf
{%   endif %}
{%   for af in ['ipv4','ipv6'] if af in vdata.af %}
{%     for rt in vdata.import %}
  route-target import vpn-{{ af }} {{ rt }}
{%     endfor %}
{%     for rt in vdata.export %}
  route-target export vpn-{{ af }} {{ rt }}
{%     endfor %}
{%   endfor %}
{%   for af in ['ipv4','ipv6'] %}
{%     for n in vdata.networks|default([]) if af in n %}
{%       if loop.index == 1 %}
  address-family {{ af }}
{%       endif %}
   network {{ n[af]|ipaddr('0') }}
{%     endfor %}
{%   endfor %}
... BGP neighbors ...
{% endfor %}

Configure BGP Neighbors

You could copy the BGP configuration template into the vrf directory and modify it to configure in-VRF BGP neighbors, or you could create a symbolic link to the Jinja2 template containing the BGP neighbor configuration macro (if it exists for your platform) within the bgp directory and use common code to configure BGP neighbors. The latter approach is recommended as it ensures feature parity between global- and in-VRF BGP neighbors.

To configure BGP neighbors, iterate over the vrfs.vname.bgp.neighbors dictionary and configure the neighbors. Cisco IOS configuration syntax results in a streamlined process:

{% import "ios.bgp-macro.j2" as bgpcfg %}
!
router bgp {{ bgp.as }}
{% for vname,vdata in vrfs.items() %}
{%   for af in ('ipv4','ipv6') if af in vdata.af %}
 address-family {{ af }} vrf {{ vname }}
... other BGP parameters ...
{%     for n in vdata.bgp.neighbors|default([]) if af in n %}
{{       bgpcfg.neighbor_global(n,n[af]) }}
{{       bgpcfg.neighbor_af(n,n[af],bgp) }}
{%     endfor %}
{%   endfor %}
{% endfor %}

Arista EOS is a bit more complex: BGP neighbors are defined in the BGP VRF configuration mode and activated within the in-VRF address family:

{% import "eos.bgp-macro.j2" as bgpcfg %}
!
router bgp {{ bgp.as }}
{% for vname,vdata in vrfs.items() %}
!
 vrf {{ vname }}
... other BGP parameters ...
{%   for n in vdata.bgp.neighbors|default([]) %}
{%     for af in ['ipv4','ipv6'] if n[af] is defined %}
{{       bgpcfg.neighbor(n,n[af],bgp) }}
{%     endfor %}
{%   endfor %}
{%   for af in ['ipv4','ipv6'] %}
... other AF parameters ...
{%     for n in vdata.bgp.neighbors|default([]) if n[af] is defined %}
{%       if loop.index == 1 %}
  address-family {{ af }}
{%       endif %}
   neighbor {{ n[af] }} activate
{%     endfor %}
{%   endfor %}
{% endfor %}

Configure OSPF

You could use the same shared macro approach to configure VRF OSPF interface, but it’s probably simpler to just copy-paste the global OSPF configuration code and change OSPF process ID (or a similar configuration construct) to refer to in-VRF OSPF process:

  • The main VRF template uses vdata variable to refer to the VRF parameters – OSPF parameters are available within vdata.ospf dictionary.

  • Use vdata.vrfidx as the OSPF process ID

  • Use vdata.ospf.router_id (or ospf.router_id) to set the router ID

  • Redistribute BGP into OSPF if the bgp.as parameter is set (the device is running BGP)

  • You don’t have to redistribute connected subnets into OSPF – interfaces that should be included in the OSPF process will be listed in the vdata.ospf.interfaces list.

  • Use global ospf.reference_bandwidth

The list of OSPF-enabled VRF interfaces is in vdata.ospf.interfaces list. Use that list in the same way you’d use the global ospf.interfaces list.

Cisco IOS example (Arista EOS example is almost identical):

!
router ospf {{ vdata.vrfidx }} vrf {{ vname }}
 router-id {{ vdata.ospf.router_id|default(ospf.router_id) }}
{% if ospf.reference_bandwidth is defined %}
 auto-cost reference-bandwidth {{ ospf.reference_bandwidth }}
{% endif %}
{% for l in vdata.ospf.interfaces|default([]) if l.ospf.passive|default(False) %}
 passive-interface {{ l.ifname }}
{% endfor %}
{% if bgp.as is defined %}
 redistribute bgp {{ bgp.as }} subnets
{% endif %}
!
{% for l in vdata.ospf.interfaces|default([]) if 'ospf' in l and 'ipv4' in l %}
interface {{ l.ifname }}
! {{ l.name|default("") }}
 ip ospf {{ vdata.vrfidx }} area {{ l.ospf.area }}
{%   if l.ospf.network_type is defined %}
 ip ospf network {{ l.ospf.network_type }}
{%   endif %}
{%   if l.ospf.cost is defined %}
 ip ospf cost {{ l.ospf.cost }}
{%   endif %}
{%   if l.ospf.bfd|default(False) %}
 ip ospf bfd
{%   endif %}
!
{% endfor %}