Huawei Quidway NetEngine80E Configuration Manual page 768

HUAWEI NetEngine80E/40E Router
Configuration Guide - IP Routing
8.
9.
10. Prefers the route with the shortest Cluster_List.
11. Prefers the route advertised by the device with the smallest router ID.
12. Prefers the route learned from the peer with the smallest address if the IP addresses of peers
Principles for BGP Route Advertisement
On the NE80E/40E, BGP advertises routes based on the following principles:
l
l
Issue 02 (2014-09-30)
l A route without MED is assigned a MED of 0, unless the bestroute med-none-as-
maximum command is run. If the bestroute med-none-as-maximum command is run,
the route is assigned the highest MED of 4294967295.
l After compare-different-as-med command is run, the MEDs in routes received from
peers in different ASs are compared. If this command is run without first confirming
that different ASs use the same IGP and route selection mode, a loop may occur.
l If the bestroute med-confederation command is run, MEDs are compared for routes
that consist only of AS_CONFED_SEQUENCE. The first AS number in the
AS_CONFED_SEQUENCE must be the same for the routes.
l After the deterministic-med command is run, routes are not selected in the sequence
in which routes are received.
Prefers EBGP routes over IBGP routes.
EBGP is higher than IBGP, IBGP is higher than LocalCross, and LocalCross is higher than
RemoteCross.
If the export route target (ERT) of a Virtual Private Network version 4 (VPNv4) route in
the routing table of a VPN instance on a provider edge (PE) matches the import route target
(IRT) of another VPN instance on the PE, the VPNv4 route will be added to the routing
table of the second VPN instance. This is called LocalCross. If the ERT of a VPNv4 route
from a remote PE is learned by the local PE and matches the IRT of a VPN instance on the
local PE, the VPNv4 route will be added to the routing table of that VPN instance. This is
called RemoteCross.
Prefers the route with the lowest IGP metric to the BGP next hop.
After the bestroute igp-metric-ignore command is run, the IGP metrics are not compared
for routes during route selection.
NOTE
Assume that load balancing is configured. If the preceding rules are the same and there are multiple
external routes with the same AS_Path, load balancing will be performed based on the number of
configured routes.
NOTE
By default, Cluster_List takes precedence over Originator_ID during BGP route selection. To enable
Originator_ID to take precedence over Cluster_List during BGP route selection, run the bestroute
routerid-prior-clusterlist command.
NOTE
If routes carry the Originator_ID, the originator ID is substituted for the router ID during route
selection. The route with the smallest Originator_ID is preferred.
are compared in the route selection process.
When there are multiple active routes, the BGP speaker advertises only the optimal route
to its peer.
The BGP speaker advertises only the preferred routes to its peer.
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8 BGP Configuration
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