nx.os.and.cisco.nexus.switching.2nd.edition.1587143046

methods are discussed from a high-level standpoint; additional details for RHI and Null
Aggregation are outside the scope of this book. LISP is covered in detail in Chapter 13,
“LISP.”
One simple way to redirect traffic to a specific IP address in an OTV extended VLAN
environment is to dynamically inject a host route for the individual endpoint IP address into
the routing protocol. Load balancers with the RHI function implemented on them can
provide an automated mechanism for detecting real-server reachability, dynamically
reacting to moves (VM-Mobility) and injecting the necessary host routes as applicable. In an
OTV environment, this allows remote hosts and routers to use this routing-specific
information to take the most optimal path to a specific IP address that is part of an extended
VLAN. When combined with FHRP isolation, this enables complete end-to-end routing
symmetry.
Note
This approach, although simple, pollutes the routing tables considerably and causes a
large amount of churn in the routing protocol. Forcing churning of the routing protocol
is a risky proposition because it can lead to instabilities and overall loss of
connectivity, together with adding delays to roaming handoffs.
Null Aggregation provides another extremely simple mechanism for providing optimal
inbound path selection. In a Null Aggregation deployment for a typical dual-DC deployment
leveraging OTV, a VLAN’s Layer 3 subnet is logically split into two more specific subnets
along a logical boundary—creating two logical ranges of IP addresses—one range to be
used per site. Hosts at each site are addressed inside of that site’s specific range but retain
the larger subnet mask and the same default gateway. The split range boundary is statically
defined in the routing table pointing to Null0, creating a more-specific inbound path for a
particular subnet—thus drawing the traffic into a particular site in an OTV extended VLAN
environment. This method is similar to the RHI approach previously described but without
any sort of dynamic behavior. It is also bound at the subnet level and not to an individual
host level. As this method is static in nature, strict administrative oversight is required to
ensure hosts are addressed into the correct IP range to maintain symmetry.
Due to this, the Null Aggregation approach works well in OTV deployments leveraging
geographically dispersed clusters because IP addresses would stay “stuck” to a particular
site. This method quickly breaks in VM-Mobility environments as individual IP addresses
float dynamically between sites.
Example 11-24 shows the Null route information for Datacenter 1.
Example 11-24. Null Aggregation Datacenter 1 Configuration Example Leveraging the
Subnet 10.1.64.0/24 and EIGRP for Redistribution
Click here to view code image