JUNOS Enterprise Routing

Asymmetric Link Speed Support

The use of asymmetric link speeds for redundant attachment to the same provider is common in both models. When running BGP, the bandwidth community can be used to provide unequal cost load balancing proportionate to the link speed. In contrast, static routing over asymmetric links is typically done by directing all traffic over the high-speed link until it becomes unavailable, at which point the traffic is switched to the lower-speed secondary. In JUNOS software, this is accomplished with a static route along with a qualified next hop. A qualified next hop is a list of next hops with varying preferences/metrics that are used in order of their preference, based on the ability to resolve the associated next hop. The following code snippet shows how a dual-homed customer could configure all traffic to egress on a high-speed T3 link, unless the T3 interface/next hop becomes unavailable, at which point the traffic will switch to the qualified next hop with the next most preferred (next lowest) preference:

[edit routing-options static]
ruser@router#show
route 0.0.0.0/0 {
    qualified-next-hop 10.0.1.1 {
        preference 20;
        interface t3-1/0/0.0;
    }
    qualified-next-hop 10.0.1.5 {
        preference 30;
        interface t1-2/0/0.0;
    }
}

Which Routers Should Run IBGP?

Great! You’ve made it this far, which shows that you still feel your network either justifies use of BGP, or simply needs a puppy. From this point forward, this chapter assumes a network that is dual-homed to multiple providers, ...