Huawei S6700 Series Configuration Manual page 384

S6700 Series Ethernet Switches
Configuration Guide - IP Routing
number of next-hop addresses to forward packets. BGP load balancing based on iteration does
not need to be configured by using commands. This feature is always enabled on the S6700.
BGP load balancing is different from IGP load balancing in the following implementation
methods:
l
l
Route Summarization
On a large-scale network, the BGP routing table is large. You can configure route summarization
to reduce the size of the routing table.
Route summarization is the process of consolidating multiple routes into one single
advertisement. After route summarization is configured, BGP advertises only the summarized
route rather than all specific routes to its peers.
The S6700 supports automatic summarization and manual summarization. Manual
summarization can be used to control attributes of the summarized route and determine whether
to advertise its specific routes.
Synchronization Between IBGP and IGP
Synchronization between IBGP and IGP is a method of preventing external routes from being
imported by error.
If the synchronization function is configured, the IGP routing table is examined before an IBGP
route is added to the routing table and advertised to EBGP peers. The IBGP route is added to
the routing table and advertised to EBGP peers only when the IGP knows this IBGP route.
The synchronization function can be disabled in the following situations:
l
l
Issue 01 (2012-03-15)
In IGPs, if there are different routes to the same destination address, an IGP calculates
metrics of these routes based on its own routing algorithm and performs load balancing
among the routes with the same metric.
BGP does not have a routing algorithm. Therefore, BGP cannot determine whether to
perform load balancing among routes based on explicit metrics. BGP, however, contains
many route attributes, which have different priorities in route selection policies. Therefore,
BGP performs load balancing according to route selection policies. That is, load balancing
is performed according to the configured maximum number of equal-cost routes only when
all the routes have the same high preference.
NOTE
l By default, BGP performs load balancing only among the routes with the same AS_Path attribute. You
can use the bestroute as-path-ignore
command to configure BGP not to compare the AS_Path attribute of routes when performs load
balancing.
l BGP load balancing is also applicable between ASs in a confederation.
The local AS is not a transit AS.
Full-mesh IBGP connections are established between all switchs in the local AS.
NOTE
In the S6700, the synchronization function is disabled by default.
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