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Example: Configuring Static Route Preferences and Qualified Next Hops

Understanding Static Route Preferences and Qualified Next Hops

A static route destination address can have multiple next hops associated with it. In this case, multiple routes are inserted into the routing table, and route selection must occur. Because the primary criterion for route selection is the route preference, you can control the routes that are used as the primary route for a particular destination by setting the route preference associated with a particular next hop. The routes with a lower route preference are always used to route traffic. When you do not set a preferred route, traffic is alternated between routes in round-robin fashion.

In general, the default properties assigned to a static route apply to all the next-hop addresses configured for the static route. If, however, you want to configure two possible next-hop addresses for a particular route and have them treated differently, you can define one as a qualified next hop.

Qualified next hops allow you to associate one or more properties with a particular next-hop address. You can set an overall preference for a particular static route and then specify a different preference for the qualified next hop. For example, suppose two next-hop addresses (10.10.10.10 and 10.10.10.7) are associated with the static route 192.168.47.5/32. A general preference is assigned to the entire static route, and then a different preference is assigned to only the qualified next-hop address 10.10.10.7. For example:

In this example, the qualified next hop 10.10.10.7 is assigned the preference 2, and the next-hop 10.10.10.10 is assigned the preference 6.

Note: The preference and metric options only apply to the qualified next hops. The qualified next-hop preference and metric override the route preference and metric (for that specific qualified next hop), similar to how the route preference overrides the default preference and metric (for that specific route).

Example: Configuring Static Route Preferences and Qualified Next Hops

This example shows how to control static route selection.

• Requirements
• Overview
• Configuration
• Verification

Requirements

In this example, no special configuration beyond device initialization is required.

Overview

In this example, the static route 192.168.47.0/24 has two possible next hops. Because one link has higher bandwidth, this link is the preferred path. To enforce this preference, the qualified-next-hop statement is included in the configuration on both devices. See Figure 1.

Figure 1: Controlling Static Route Selection

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Step-by-Step Procedure

1. On Device B, configure the interfaces.
   [edit interfaces]user@B# set ge-1/2/0 unit 0 description B->Duser@B# set ge-1/2/0 unit 0 family inet address 172.16.1.1/24user@B# set fe-1/2/1 unit 2 description secondary-B->Duser@B# set fe-1/2/1 unit 2 family inet address 192.168.2.1/24user@B# set lo0 unit 57 family inet address 10.0.0.1/32user@B# set lo0 unit 57 family inet address 10.0.0.2/32
2. On Device B, configure a static route to the customer network.
   [edit routing-options static route 192.168.47.0/24]user@B# set next-hop 172.16.1.2
3. On Device B, configure a backup route to the customer network.
   [edit routing options static route 192.168.47.0/24]user@B# set qualified-next-hop 192.168.2.2 preference 25
4. On Device D, configure the interfaces.
   [edit interfaces]user@D# set ge-1/2/0 unit 1 description D->Buser@D# set ge-1/2/0 unit 1 family inet address 172.16.1.2/24user@D# set fe-1/2/1 unit 3 description secondary-D->Buser@D# set fe-1/2/1 unit 3 family inet address 192.168.2.2/24user@D# set lo0 unit 2 family inet address 192.168.47.5/32user@D# set lo0 unit 2 family inet address 192.168.47.6/32
5. On Device D, configure a static default route to external networks.
   [edit routing options static route 0.0.0.0/0]user@D# set next-hop 172.16.1.1
6. On Device D, configure a backup static default route to external networks.
   [edit routing options static route 0.0.0.0/0]user@D# set qualified-next-hop 192.168.2.1 preference 25

Results

Confirm your configuration by issuing the show interfaces and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

inet.0: 7 destinations, 8 routes (7 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

192.168.47.0/24    *[Static/5] 02:02:03
                    > to 172.16.1.2 via ge-1/2/0.0
                    [Static/25] 01:58:21
                    > to 192.168.2.2 via fe-1/2/1.2

inet.0: 7 destinations, 8 routes (7 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

0.0.0.0/0          *[Static/5] 02:02:12
                    > to 172.16.1.1 via ge-1/2/0.1
                    [Static/25] 01:58:31
                    > to 192.168.2.1 via fe-1/2/1.3

PING 192.168.47.5 (192.168.47.5): 56 data bytes
64 bytes from 192.168.47.5: icmp_seq=0 ttl=64 time=156.126 ms
64 bytes from 192.168.47.5: icmp_seq=1 ttl=64 time=120.393 ms
64 bytes from 192.168.47.5: icmp_seq=2 ttl=64 time=175.361 ms

PING 10.0.0.1 (10.0.0.1): 56 data bytes
64 bytes from 10.0.0.1: icmp_seq=0 ttl=64 time=1.315 ms
64 bytes from 10.0.0.1: icmp_seq=1 ttl=64 time=31.819 ms
64 bytes from 10.0.0.1: icmp_seq=2 ttl=64 time=1.268 ms