Re: ARP , CEF and /32 route

There is no order of preference between an ARP entry and a route. ARP
is just a layer 3 to layer 2 mapping. CEF doesn't install ARP entries,
it install routes in the FIB. This is similar to Frame Relay in that a
Frame Relay mapping doesn't install a /32 route to the destination.

In your case you've told the router that 192.168.0.100/32 can be reached
via 192.168.1.2 so why would you ever want it to route out another
interface? The most specific route is going to win, ARP entry or not.
If this wasn't the case someone could inject ARP entries to override the
routing table ;-) Talk about a mess.

-- 
Brian Dennis, CCIEx5 #2210 (R&S/ISP-Dial/Security/SP/Voice)
bdennis_at_ine.com
Internetwork Expert, Inc.
http://www.INE.com
On 03/04/2012 06:51 PM, Bernard Steven wrote:
> Hello Experts,
>
> in a router ,
>
> int gig 0/0
> ip address 192.168.0.1 255.255.255.0
>
>
> int gig 0/1
> ip address 192.168.1.1 255.255.255.0
>
>
>
> ip route 192.168.0.100 255.255.255.255 192.168.1.2
>
> and i see an arp learned from the int gig 0/0 for 192.168.0.100
> the cef table points to the static route pointing to the gig0/1
>
>
> my question is what is the order of preference when building the cef ?
> It seems like router uses the /32 route instead of the ARP entry.
>
> is there a way we could forced the router to use the ARP entry instead of
> the /32 ?
>
>
> and the same question if a /32 route exists to null0 , and the router has
> an arp entry for the same host.
>
> Regards
>
>
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