Configuring As_Path Attributes For Routes - Huawei Quidway NetEngine80E Configuration Manual

HUAWEI NetEngine80E/40E Router
Configuration Guide - IP Routing
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8.4.7 Configuring AS_Path Attributes for Routes

The AS_Path attribute is used to prevent routing loops and control route selection.
Procedure
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Issue 02 (2014-09-30)
In the inter-AS VPN option C networking where route reflectors (RRs) are used, the
peer next-hop-invariable command needs to be run to prevent the RRs from changing
the next-hop address of a route when the RRs advertise the route to EBGP peers. This
ensures that the remote PE iterates a route to the BGP Label Switched Path (LSP)
destined for the local PE during traffic transmission.
Configure routing-policy-based next hop iteration.
1. Run:
system-view
The system view is displayed.
2. Run:
bgp { as-number-plain | as-number-dot }
The BGP view is displayed.
3. Run:
ipv4-family unicast
The IPv4 unicast address family view is displayed.
4. Run:
nexthop recursive-lookup route-policy route-policy-name
Routing-policy-based next hop iteration is configured.
By default, routing-policy-based next hop iteration is not configured.
Next-hop iteration based on a specified routing policy can control the iterated next
hop based on specific conditions. If a route cannot match the specified routing policy,
the route cannot be iterated.
Allow repeated local AS numbers.
BGP uses AS numbers to detect routing loops. In Hub and Spoke networking, if EBGP
runs between a Hub-PE and a Hub-CE, the route sent from the Hub-PE to the Hub-CE
carries the AS number of the Hub-PE. After the Hub-CE sends an Update message that
contains the AS number of the Hub-PE to the Hub-PE, the Hub-PE will deny it.
To ensure proper route transmission in Hub and Spoke networking, configure all the BGP
peers on the path, along which the Hub-CE advertises private network routes to the Spoke-
CE, to accept the routes in which the local AS number repeats once.
1. Run:
system-view
The system view is displayed.
2. Run:
bgp { as-number-plain | as-number-dot }
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8 BGP Configuration
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