Routing

Can anyone explain what the resolve keyword does in a static route statement?

I am looking at an example in the Junos Routing Essentials course and it does not explain it very well.

It says that Junos does not do recurssive lookups of next hops by default?

Can anyone clarify or point me to some documentation?

Thanks

Roger

I am a cisco guy and studying for my CCIE but this does not make sense

Hi,

Not much links found

http://www.juniper.net/techpubs/en_US/junos10.0/information-products/topic-collections/config-guide-routing/routing-configuring-static-route-options.html

By default, static routes can point only to a directly connected next hop. You can configure an IPv4 route to a prefix that is not directly connected by resolving the route through the inet.0 and inet.3 routing tables. To configure an IPv4 static route to a prefix that is not a directly connected next hop, include the resolve statement:

- it means that you could configure any static route on direct connect IP only but if you want to make the next-hop of this static route on another router for example you couldn't by default and need resolve so the router will look on the routing table for this next-hop and if exist so the route will be valid and could forward traffic

Regards,

Mohamed Elhariry

JNCIE-M/T # 1059, CCNP & CCIP

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If this post was helpful, please mark this post as an "Accepted Solution".Kudos are always appreciated!

By default, the Junos OS requires that the next-hop IP address of static routes be reachable using a direct route. Unlike software
from other vendors, the Junos OS does not perform recursive lookups of next hops by default.

As illustrated in the graphic, you can alter the default next-hop resolution behavior using the resolve CLI option. In addition to the resolve CLI option, a route to the indirect next hop is also required. Indirect next hops can be resolved through another
static route or through a dynamic routing protocol. We recommend, whenever possible, that you use a dynamic routing protocol as your method of resolution. Using a dynamic routing protocol, rather than a static route to resolve indirect next hops,
dynamically removes the static route if the indirect next hop becomes unavailable.

JNCIA-Junos Study Guide—Part 2/Chapter 1: Routing Fundamentals /Resolving Indirect Next Hops/ PAGE-19

zoher kettab

  Cisco automatically resolve recursive routes. Those which next hop is not under directly connected interface. But Junos dont behave this way, so you have to configure the resolve option.

   For example, cisco config using recursive routes :

      ip route 1.1.1.0 255.255.255.0 2.2.2.2

      ip route 2.2.2.0 255.255.255.0 3.3.3.3

      interface fastethernet 0/0

        ip add 3.3.3.1 255.255.255.0

    Usually the second static route is some dynamic learned route, this have no sense to configure two recursive statics.

    Under Junos this config will be something like this :

      set routing-options static route 1.1.1.0/24 next-hop 2.2.2.2 resolve

      set routing-options static route 2.2.2.0/24 next-hop 3.3.3.3

      set interface fe-0/0/0 unit 0 family inet address 3.3.3.1/24

        If you dont use the resolve option, the first static router will be hidden because this have no an active next hop.

Excerpt from JER Book by Dough Marschke & Harr Reynolds

"

resolve
The resolve keyword allows you to define an indirect next hop for a static route,
which is to say an IP forwarding address that does not resolve to a directly connected
interface route. For example, you could specify a static route that points to
a downstream neighbor’s loopback address. In this case, matching traffic will result
in a recursive lookup against the specified (lo0) next hop to select a directly connected
forwarding next hop. If a parallel connection exists, the failure of the currently
used link results in a new recursive lookup and selection of the remaining
link for packet forwarding."