Figure 1 shows a Layer 3 DC model, where a VPRN is defined in the DGWs, connecting the tenant to the WAN. That VPRN instance is connected to the VPRNs in the NVEs by means of an IRB backhaul R-VPLS. Because the IRB backhaul R-VPLS provides connectivity only to all the IRB interfaces and the DGW VPRN is not directly connected to all the tenant subnets, the WAN ip-prefixes in the VPRN routing table must be advertised in EVPN. In the same way, the NVEs send IP prefixes in EVPN that is received by the DGW and imported in the VPRN routing table.
Local router interface host addresses are not advertised in EVPN by default. To advertise them, the ip-route-advertisement incl-host command must be enabled. For example:
===============================================================================
Route Table (Service: 2)
===============================================================================
Dest Prefix[Flags] Type Proto Age Pref
Next Hop[Interface Name] Active Metric
-------------------------------------------------------------------------------
10.1.1.0/24 Local Local 00h00m11s 0
if Y 0
10.1.1.100/32 Local Host 00h00m11s 0
if Y 0
==============================================================================
For the case displayed by the output above, the behavior is the following:
ip-route-advertisement only local subnet (default) - 10.1.1.0/24 is advertised
ip-route-advertisement incl-host local subnet, host - 10.1.1.0/24 and 10.1.1.100/32 are advertised
Below is an example of VPRN (500) with two IRB interfaces connected to backhaul R-VPLS services 501 and 502 where EVPN-VXLAN runs:
vprn 500 customer 1 create
ecmp 4
route-distinguisher 65072:500
vrf-target target:65000:500
interface "evi-502" create
address 10.20.20.72/24
vpls "evpn-vxlan-502"
exit
exit
interface "evi-501" create
address 10.10.10.72/24
vpls "evpn-vxlan-501"
exit
exit
no shutdown
vpls 501 name "evpn-vxlan-501" customer 1 create
allow-ip-int-bind
vxlan instance 1 vni 501 create
exit
bgp
route-distinguisher 65072:501
route-target export target:65000:501 import target:65000:501
exit
bgp-evpn
ip-route-advertisement incl-host
vxlan bgp 1 vxlan-instance 1
no shutdown
exit
exit
no shutdown
exit
vpls 502 name "evpn-vxlan-502" customer 1 create
allow-ip-int-bind
vxlan instance 1 vni 502 create
exit
bgp
route-distinguisher 65072:502
route-target export target:65000:502 import target:65000:502
exit
bgp-evpn
ip-route-advertisement incl-host
vxlan bgp 1 vxlan-instance 1
no shutdown
exit
exit
no shutdown
exit
When the above commands are enabled, the router behaves as follows:
Receive route-type 5 routes and import the IP prefixes and associated IP next-hops into the VPRN routing table.
If the route-type 5 is successfully imported by the router, the prefix included in the route-type 5 (for example, 10.0.0.0/24), is dded to the VPRN routing table with a next-hop equal to the gateway IP included in the route (for example, 192.0.0.1. that refers to the IRB IP address of the remote VPRN behind which the IP prefix sits).
When the router receives a packet from the WAN to the 10.0.0.0/24 subnet, the IP lookup on the VPRN routing table yields 192.0.0.1 as the next-hop. That next-hop is resolved to a MAC in the ARP table and the MAC resolved to a VXLAN tunnel in the FDB table
Generate route-type 5 routes for the IP prefixes in the associated VPRN routing table.
For example, if VPRN-1 is attached to EVPN R-VPLS 1 and EVPN R-VPLS 2, and R-VPLS 2 has bgp-evpn ip-route-advertisement configured, the 7750 SR advertises the R-VPLS 1 interface subnet in one route-type 5.
Routing policies can filter the imported and exported IP prefix routes accordingly.
The VPRN routing table can receive routes from all the supported protocols (BGP-VPN, OSPF, IS-IS, RIP, static routing) as well as from IP prefixes from EVPN, as shown below:
*A:PE72# show router 500 route-table
===============================================================================
Route Table (Service: 500)
===============================================================================
Dest Prefix[Flags] Type Proto Age Pref
Next Hop[Interface Name] Metric
-------------------------------------------------------------------------------
10.20.20.0/24 Local Local 01d11h10m 0
evi-502 0
10.20.20.71/32 Remote BGP EVPN 00h02m26s 169
10.10.10.71 0
10.10.10.0/24 Remote Static 00h00m05s 5
10.10.10.71 1
10.16.0.1/32 Remote BGP EVPN 00h02m26s 169
10.10.10.71 0
-------------------------------------------------------------------------------
No. of Routes: 4
The following considerations apply:
The route Preference for EVPN IP prefixes is 169.
BGP IP-VPN routes have a preference of 170 by default, therefore, if the same route is received from the WAN over BGP-VPRN and from BGP-EVPN, then the EVPN route is preferred.
When the same route-type 5 prefix is received from different gateway IPs, ECMP is supported if configured in the VPRN.
All routes in the VPRN routing table (as long as they do not point back to the EVPN R-VPLS interface) are advertised via EVPN.
Although the description above is focused on IPv4 interfaces and prefixes, it applies to IPv6 interfaces too. The following considerations are specific to IPv6 VPRN R-VPLS interfaces:
IPv4 and IPv6 interfaces can be defined on R-VPLS IP interfaces at the same time (dual-stack).
The user may configure specific IPv6 Global Addresses on the VPRN R-VPLS interfaces. If a specific Global IPv6 Address is not configured on the interface, the Link Local Address interface MAC/IP is advertised in a route type 2 as soon as IPv6 is enabled on the VPRN R-VPLS interface.
Routes type 5 for IPv6 prefixes are advertised using either the configured Global Address or the implicit Link Local Address (if no Global Address is configured).
If more than one Global Address is configured, normally the first IPv6 address is used as gateway IP. The ‟first IPv6 address” refers to the first one on the list of IPv6 addresses shown through the show router <id> interface <interface> IPv6 or through SNMP.
The rest of the addresses are advertised only in MAC-IP routes (Route Type 2) but not used as gateway IP for IPv6 prefix routes.