[j-nsp] negative arp chache on JunOS

[Arjan Koopen]

Hi,

> On 09 Dec 2016, at 14:45, Jiri Lunacek <jiri.lunacek at hosting90.cz <mailto:jiri.lunacek at hosting90.cz>> wrote:
> 
> Has anyone found a way how to cache negative ARP results in JunOS?

Nope :(. We ran into issues before at CCC Congress (Hamburg) in 2013 when using Ruckus WiFi. We ended up replacing the Juniper router for WiFi with a Linux Router which *could* do negative ARP caching.

These days we’re using Aruba WiFi gear which can do ARP-proxying and doesn’t flood ARP requests for IPs it doesn’t know and answers on-behalf of the clients.

> The only way of working around this I could come up with was defining discard routes for all interface prefixes and then importing a host route for every active address in our network. And that is a last resort I would rather not use.

You could look at AMS-IX’s ARP-sponge: https://ams-ix.net/downloads/arpsponge/ <https://ams-ix.net/downloads/arpsponge/> - not sure if that would solve your CPU issues though, but at least it wouldn’t have to ARP anymore once the table has been filled.

— Arjan