Dell PowerConnect B-RX - Page 287

BigIron RX Series Configuration Guide 211
53-1002253-01
Configuring forwarding parameters
7
• OSPF – The Path Cost associated with the path. The paths can come from any combination of
inter-area, intra-area, and external Link State Advertisements (LSAs).
• BGP4 – The path’s Multi-Exit Discriminator (MED) value.
NOTE
If the path is redistributed between two or more of the above sources before entering the IP route
table, the cost can increase during the redistribution due to settings in redistribution filters.
Static route, OSPF, and BGP4 load sharing
IP load sharing and load sharing for static routes, OSPF routes, and BGP4 routes are individually
configured. Multiple equal-cost paths for a destination can enter the IP route table only if the
source of the paths is configured to support multiple equal-cost paths. For example, if BGP4 allows
only one path with a given cost for a given destination, the BGP4 route table cannot contain
equal-cost paths to the destination. Consequently, the IP route table will not receive multiple
equal-cost paths from BGP4.
Table 50 lists the default and configurable maximum numbers of paths for each IP route source
that can provide equal-cost paths to the IP route table. The table also lists where to find
configuration information for the route source’s load sharing parameters.
The load sharing state for all the route sources is based on the state of IP load sharing. Since IP
load sharing is enabled by default on the device, load sharing for static IP routes, RIP routes, OSPF
routes, and BGP4 routes also is enabled by default.
How IP load sharing works
On the device, IP load sharing (also known as ECMP load sharing) is done by the hardware. If there
is more than one path to a given destination, a hash is calculated based on the source MAC
address, destination MAC address, source IP address, destination IP address, and IP protocol. This
hash is used to select one of the paths.
TABLE 50 Default load sharing parameters for route sources
Route source Default maximum number of paths Maximum number of paths See...
Static IP route 4
NOTE: This value depends on the
value for IP load sharing,
and is not separately
configurable.
8
NOTE: This value depends
on the value for IP
load sharing, and is
not separately
configurable.
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RIP 4
NOTE: This value depends on the
value for IP load sharing,
and is not separately
configurable.
8
NOTE: This value depends
on the value for IP
load sharing, and is
not separately
configurable.
page 212
OSPF 4 8 page 212
BGP4 1 4 page 791