H3C Technologies H3C S10500 Series Switches - Manual (Page 274)

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NOTE:
•
If you start OSPF but do not configure the router ID, the system will automatically elect one. However, the
same election rules produce the same router ID. Therefore, H3C recommends that you configure the
router ID when starting an OSPF process. For the election rules, see Layer 3—IP Routing Configuration
Guide.
• If you configure multiple OSPF VPN instances but do not configure the route tag, the system will
automatically create one based on the AS number configured. If you do not configure BGP, the tag will
be 0. However, the same calculation rule produces the same tag, and hence the same tag will be created
for multiple OSPF VPN instances on the same PE or PEs with the same AS number. Therefore, H3C
recommends configuring different tags for different OSPF VPN instances.
Configuring BGP AS number substitution
Configuration prerequisites
Before you configure BGP AS number substitution, complete the following tasks:
• Configure basic MPLS L3VPN
• Ensure CEs at different sites to have the same AS number
Configuration procedure
When CEs at different sites have the same AS number, configure the BGP AS number substitution function
to avoid route loss.
With the BGP AS number substitution function, when a PE advertises a route to the specified CE, if an AS
number identical to that of the CE exists in the AS_PATH of the route, it will be replaced with that of the
PE before the route is advertised.
Follow these steps to configure BGP AS number substitution:
To do… Use the command… Remarks
Enter system view system-view —
Enter BGP view bgp as-number Required
Enter BGP VPN instance view
ipv4-family vpn-instance
vpn-instance-name
Required
Enable the BGP AS number
substitution function peer { ip-address | group-name }
substitute-as Required
Disabled by default
NOTE:
For more information about the peer { ip-address | group-name } substitute-as command, see Layer
3—IP Routing Command Reference.