You can configure an external BGP (EBGP) or IBGP multihop session between the PE and CE routers of a Layer 3 VPN. This allows you to have one or more routers between the PE and CE routers. Using IBGP between PE and CE routers does not require the configuration of any additional statements. However, using EBGP between the PE and CE routers requires the configuration of the multihop statement.
To configure an external BGP multihop session for the connection between the PE and CE routers, include the multihop statement on the PE router. To help prevent routing loops, you have to configure a time-to-live (TTL) value for the multihop session:
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multihop ttl-value;
For the list of hierarchy levels at which you can configure this statement, see the summary section for this statement.