EVPN Overview
BGP (Border Gateway Protocol) was standardized in
RFC 7432 and
RFC 8365 to carry Layer-2
information for virtualized networks. Ethernet virtual private network (EVPN) was
initially targeted for
MPLS (Multiprotocol Label Switching) and WAN, but later adopted as a
VXLAN (Virtual Extensible LAN) control plane protocol.
ExtremeXOS supports EVPN control plane for
VXLAN. At a high level, BGP supports the following constructs to distribute information
for any virtualized network:
- Identify the network address
family with AFI/SAFI—For VXLAN, AFI of 25 (L2VPN) and a SAFI (EVPN) of
70 is used.
- Within the address family,
identify the type of route being advertised—Different route types are
defined. For supported route types in ExtremeXOS, see Supported EVPN Route Types in ExtremeXOS.
- Identify which device
originated the route and virtual-network the route belongs to—This is
the role of the route distinguisher (RD) and route target (RT).
In
ExtremeXOS, RD is
automatically derived based on configured local-endpoint IP address and the VLAN ID of
the tenant VLAN. The VLAN ID of the tenant VLAN is also used as an EVPN instance (EVI)
index. An EVI is automatically created when a virtual network configuration is completed
and BGP is enabled. A complete virtual-network consists of a tenant VLAN, VNI, and local
endpoint IP address. RTs are automatically calculated for each EVI using the method
specified in
Section 5.1.2.1
of
RFC-8365. Because this
method uses the local AS number as part of the calculation, each router calculates
different RTs in an EBGP environment because the local AS number is different.
Note
RTs are derived automatically under
the following conditions:
- When iBGP is used and the AS
number is less than 65,535 (2 byte ASNUM).
- BGP Auto-peering is
used.
EVPN devices perform dynamic learning on the access side of a VXLAN network. The
learned MAC and ARP entries are exported to BGP as EVPN Type 2 routes. BGP advertises
the Type 2 routes to all neighbors with L2VPN-EVPN capability. A VTEP with matching RT
configured or auto-derived processes these Type 2 routes and creates static
non-permanent FDB, ARP tunnel entries. Traffic to the tunnel entries are VXLAN
encapsulated and forwarded.
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