Example: Configuring a Default Route to a Shared Interface

For the first solution you create a default route in the VRF that points to a shared IP interface. You must manually create the shared IP interface on top of the layer 2 interface that points to the Internet gateway. See Figure 102.

The main disadvantage of this approach is that if multiple Internet gateways are available, BGP cannot select the egress gateway that is optimal for each destination prefix. Because BGP has only a default route in the VRF, it has to point that single default route to a single uplink interface. All the Internet-bound traffic must flow out of that interface.

You cannot configure traffic for one prefix to flow out of one uplink interface and traffic to another prefix to flow out of another uplink interface. That behavior requires a full default-free Internet routing table in the VRF, which is a complication that you want to avoid.

Figure 102: Static Default Route for Internet Access

Static Default Route for Internet Access

The following commands illustrate how to create a shared IP interface in the VRF and point a default route to it:

host1(config)#virtual-router pe1:pe11 host1:pe1:pe11(config)#interface ip internet-access host1:pe1:pe11(config-if)#ip share-interface atm2/1.3 host1:pe1:pe11(config-if)#ip address host1:pe1:pe11(config-if)#exit host1:pe1:pe11(config)#ip route ip internet-access

See Shared IP Interfaces in the JunosE IP, IPv6, and IGP Configuration Guide, for information about shared IP interfaces and default routes.

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