Configure VRF-lite | Page 55
Configuring a complex inter-VRF solution
Connected routes associated with VRF green are redistributed into BGP, and also advertised
to the external BGP neighbor router. VRF green has an i-BGP peering relationship to its
neighbor as the neighbor ASN is the same (ASN 100). BGP routes learned from the external
i-BGP neighbor are added to BGP 100. As the connection is i-BGP (not e-BGP), the BGP
command next-hop-self is required to ensure the next-hop IP address is modified for each
prefix advertised to the external i-BGP peer. The next hop address becomes the VRF green
vlan2 ip address ‘192.168.20.1’. Without this command inter-VRF routes advertised to the
external i-BGP peer would retain the original next-hop IP address associated with VRF
shared.
For example, the i-BGP standard dictates that without the command next-hop-self
, the VRF
shared route 192.168.44.0/24 leaked into VRF green would be advertised to the external
VRF green i-BGP peer retaining the original VRF shared next-hop IP 192.168.100.2, instead of
being modified to become the VRF green vlan2 IP 192.168.20.1.
The e-BGP standard dictates that the next-hop IP is automatically modified when advertising
a prefix to an e-BGP neighbor, so the command next-hop-self
is not required for external e-
BGP peering relationships.
The default-originate
command is required to ensure BGP redistributes the VRF green static
default route to VRF green external i-BGP neighbor.
Connected routes and RIPv2 routes associated with VRF blue are imported and
redistributed into BGP to be leaked to VRF shared.
Connected routes, OSPF instance 2 routes, and the static route associated with VRF orange
are redistributed into BGP. VRF orange also has two static routes to orange router subnets
192.168.140.0/24 and 192.168.20.0/24. Only static route 192.168.140.0/24 is redistributed
into BGP. Previously, VRF orange static route 192.168.20.0/24 was filtered via VRF export
ACL as the network address range is also used elsewhere - with VRF green vlan2.
Connected routes and static routes associated with VRF shared are redistributed into BGP.
VRF shared has static routes to external shared router networks 192.168.43.0/24,
192.168.44.0/24 and 192.168.45.0/24 as well as a static default route to the Internet. VRF
shared has an e-BGP peering relationship to its internet-facing neighbor as the neighbor ASN
is different (peer ASN = 300 instead of 100). The external Internet router learns routes to all
networks associated with VRFs red, green, blue and orange via the e-BGP peering
relationship.
Note: A unique AS number (ASN) is allocated to each AS for use in BGP routing. The
numbers are assigned by IANA and the Regional Internet Registries (RIR), the same
authorities that allocate IP addresses. There are public numbers, which may be used
on the Internet and range from 1 to 64511, and private numbers from 64512 to
65535, which can be used within an organization.
