Lenovo ThinkSystem NE2552E, Application Manual

Page: 403 / 574

© Copyright Lenovo 2018 Chapter 28: OSPF
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Host Routes for Load Balancing
Lenovo ENOS implementation of OSPF includes host routes. Host routes are used
for advertising network device IP addresses to external networks, accomplishing
the following goals:
 ABR Load Sharing
As a form of load balancing, host routes can be used for dividing OSPF traffic
among multiple ABRs. To accomplish this, each switch provides identical
services but advertises a host route for a different IP address to the external
network. If each IP address serves a different and equal portion of the external
world, incoming traffic from the upstream router should be split evenly among
ABRs.
 ABR Failover
Complementing ABR load sharing, identical host routes can be configured on
each ABR. These host routes can be given different costs so that a different ABR
is selected as the preferred route for each server and the others are available as
backups for failover purposes.

Equal Cost Multipath (ECMP)
With equal cost multipath, a router potentially has several available next hops
towards any given destination. ECMP allows separate routes to be calculated for
each IP Type of Service. All paths of equal cost to a given destination are
calculated, and the next hops for all equal ‐ cost paths are inserted into the
routing table.
If redundant routes via multiple routing processes (such as OSPF, RIP, BGP, or
static routes) exist on your network, the switch defaults to the OSPF ‐ derived route.
Loopback Interfaces in OSPF
Because loopback interfaces are always available on the switch, loopback interfaces
may present an advantage when used as the router ID.
If dynamic router ID selection is used (see “Router ID” on page 399 ), loopback
interfaces can be used to force router ID selection. If a loopback interface is
configured, its IP address is automatically selected as the router ID, even if other IP
interfaces have lower IP addresses. If more than one loopback interface is
configured, the lowest loopback interface IP address is selected.
Loopback interfaces can be advertised into the OSPF domain by specifying an
OSPF host route with the loopback interface IP address.
To enable OSPF on an existing loopback interface:
NE2552E(config)# interface loopback
<1 ‐ 5
>
NE2552E(config-ip-loopback)# ip ospf area
<area ID>
enable
NE2552E(config-ip-loopback)# exit