[c-nsp] ARP strangeness

[Phil Mayers]

On 19/01/11 07:47, Frank Bulk - iName.com wrote:
> Keegan:
>
>
>
> You're correct - without broadcast support, re-population initiated from the
> 7609 is impossible.  Once it's expired, the FTTH access gear's design, which
> blocks broadcast traffic, makes it impossible for the CPE to respond to the

I'm confused; Rodney mentioned up-thread that, in "newer" IOS, the 
behaviour is different than many (myself included) had assumed. If I 
understood him correctly:

  1. At expiry - 60 seconds, attempt to renew the ARP entry via unicast
  2. At expiry, attempt to renew the ARP entry via broadcast

Shouldn't the first step flow through the FTTH gear fine, and renew the 
FDB entry?


Anyway - this is vile, but have you considered pinging the CPE from a 
separate device as a way to keep the FDB entry alive?

We do this to keep "quiet hosts" in the FDB on our switches because the 
mac-based-vlan implementation we're using is tied to FDB entry (not link 
up/down state) and if a host goes quiet (like a printer not used in 5 
minutes) the FDB entry (and vlan assignment) will expiry, and 
unless/until the *host* sends a packet (which may be never) it's 
unreachable.

We use "fping" every 4 minutes on 2 servers (offset by 2 minutes, so a 
ping arrives every 120 nseconds) for this. We extract the IP addresses 
from our registration database, but you could perhaps script it from a 
walk of the 7600 ARP table (maybe even filter by OUI or MAC of the 
devices you know need it?).

Just a thought...