KB.15.15

Example 123 Example of show ip route command output with multiple next-hop routes

HP Switch show ip route

IP Route Entries

Destination Gateway VLAN Type Sub-Type Metric Dist.

------------------ --------------- ---- --------- ---------- ---------- -----

1.0.0.0/8 10.0.8.1 1 static 1 1

10.0.8.0/21 DEFAULT_VLAN 1 connected 1 0

12.0.9.0/24 VLAN3 3 connected 1 0

15.0.0.0/8 10.0.8.1 1 static 1 1

21.0.9.0/24 162.130.101.2 2 ospf IntraArea 2 110

21.0.9.0/24 162.130.101.3 2 ospf IntraArea 2 110

21.0.9.0/24 162.130.101.4 2 ospf IntraArea 2 110

127.0.0.0/8 reject static 0 0

127.0.0.1/32 lo0 connected 1 0

162.130.101.0/24 VLAN2 2 connected 1 0

For a given destination network in an OSPF domain, multiple ECMP next-hop routes can be one

of the following types.

• Intra-area (routes to the destination in the same OSPF area)

• Inter-area (routes to the destination through another OSPF area)

• External (routes to the destination through another AS)

Multiple ECMP next-hop routes cannot be a mixture of intra-area, inter-area, and external routes.

For example, in Example 123 (page 197), the multiple next-hop routes to network 21.0.9.0/24

are all intra-area.

Also, according to the distributed algorithm used in the selection of ECMP next-hop routes:

• Intra-area routes are preferred to inter-area routes.

• Inter-area routes are preferred to external routes through a neighboring AS.

In addition, ECMP ensures that all traffic forwarded to a given host address follows the same path,

which is selected from the possible next-hop routes.

For example, in Figure 41 (page 198), the ECMP inter-area routes to destination network

10.10.10.0/24 consist of the following next-hop gateway addresses: 12.0.9.2, 13.0.9.3, and

14.0.9.4.

Equal cost multi-path routing (ECMP) 197