Owner's Manual

598 | Chapter 20. IPv4 Unicast Routing
NETGEAR 8800 User Manual
Note: Although these priorities can be changed, do not attempt any
manipulation unless you are expertly familiar with the possible
consequences.
IP Route Sharing and ECMP
IP route sharing allows a switch to communicate with a destination through multiple
equal-cost routes. In OSPF and BGP, this capability is referred to as equal cost multipath
(ECMP) routing.
Without IP route sharing, each IP route entry in the routing tables lists a destination subnet
and the next-hop gateway that provides the best path to that subnet. Every time a packet is
forwarded to a particular destination, it uses the same next-hop gateway.
With IP route sharing, an additional ECMP table lists up to 2, 4, or 8 next-hop gateways
(depending on the platform and feature configuration) for each route in the routing tables.
When multiple next-hop gateways lead to the same destination, the switch can use any of
those gateways for packet forwarding. IP route sharing provides route redundancy and can
provide better throughput when routes are overloaded.
The gateways in the ECMP table can be defined with static routes, or they can be learned
through the OSPF or BGP protocols. For more information on the ECMP table, see
ECMP
Hardware Table on page 609.
Table 57. Relative Route Priorities
Route Origin Priority
Direct 10
BlackHole 50
Static 1100
ICMP 1200
EBGP 1700
IBGP 1900
OSPFIntra 2200
OSPFInter 2300
RIP 2400
OSPFExtern1 3200
OSPFExtern2 3300
BOOTP 5000