Routing Policies for BGP EVPN IP Prefixes

BGP routing policies are supported for IP prefixes imported or exported through BGP-EVPN in R-VPLS services (EVPN-IFF routes) or VPRN services (EVPN-IFL routes).

When applying routing policies to control the distribution of prefixes between EVPN-IFF and IP-VPN (or EVPN-IFL), the user must consider that these owners are completely separate as far as BGP is concerned and when prefixes are imported in the VPRN routing table, the BGP attributes are lost to the other owner, unless the iff-attribute-uniform-propagation command is configured on the router.

If the iff-attribute-uniform-propagation command is disabled, the use of route tags allows the controlled distribution of prefixes across the two families.

Figure 1 shows an example of how VPN-IPv4 routes are imported into the RTM (Routing Table Manager) and then passed to EVPN for its own process.

Note:

VPN-IPv4 routes can be tagged at ingress and that tag is preserved throughout the RTM and EVPN processing so that the tag can be matched at the egress BGP routing policy.

Figure 1. IP-VPN Import and EVPN Export BGP Workflow

Policy tags can be used to match EVPN IP prefixes that were learned not only from BGP VPN-IPv4 but also from other routing protocols. The tag range supported for each protocol is different, as follows:

<tag>  : accepts in decimal or hex
        [0x1..0xFFFFFFFF]H (for OSPF and IS-IS)
        [0x1..0xFFFF]H (for RIP)
        [0x1..0xFF]H (for BGP)

Figure 2 shows an example of the reverse workflow where routes are imported from EVPN and exported from RTM to BGP VPN-IPv4.

Figure 2. EVPN Import and I-VPN Export BGP Workflow

The preceding described behavior and the use of tags is also valid for vsi-import and vsi-export policies in the R-VPLS.

The following is a summary of the policy behavior for EVPN-IFF IP-prefixes when iff-attribute-uniform-propagation is disabled.

For EVPN-IFF routes received and imported in RTM, policy entries (peer or vsi-import) match on communities or any of the following fields, and can add tags (as action):
- communities, extended-communities or large communities
- well-known communities
- family EVPN
- protocol bgp-vpn
- prefix-lists
- EVPN route type
- BGP attributes (as-path, local-preference, next-hop)
For exporting RTM to EVPN-IFF prefix routes, policy entries only match on tags, and based on this matching, add communities, accept, or reject. This applies to the peer level or on the VSI export level. Policy entries can also add tags for static routes, RIP, OSPF, IS-IS, BGP, and ARP-ND routes, which can then be matched on the BGP peer export policy, or on the VSI export policy for EVPN-IFF routes.

The following applies if the iff-attribute-uniform-propagation command is enabled.

For exporting RTM to EVPN-IFF prefix routes, in addition to matching on tags, matching path attributes on EVPN-IFF routes is supported in the following:

vrf-export (when exporting the prefixes in VPN-IP or EVPN IFL or IP routes)
vsi-export policies (when exporting the prefixes in EVPN-IFF routes)
for non-BGP route-owners (RIP, OSPF, IS-IS, static, ARP-ND), there are no changes and the only match criteron in vsi-export for EVPN-IFF routes is tags