[c-nsp] ARP strangeness

[Keegan Holley]

The 7600 should stop arping if it has gotten a reply.  What happens when you ping your test CPE both from the router and from another node behind it?  You can also run he command sh ip cef exact-match to see what the router is doing with a specific source-destination ip pair. If nothing strange pops up then it's probably a bug.

Sent from my iPhone

On Jan 3, 2011, at 12:58 PM, Frank Bulk <frnkblk at iname.com> wrote:

> We have over a thousand FTTH customers hanging off a VLAN on our 7609-S
> running 12.2SRE3.  Those who have Linksys BEFRS41 (wired-only routers) are
> complaining about lack of Internet access after many hours or days of idle
> time (not using their PC or other devices).  Those who have Linksys WRT54G
> (wireless) have no complaints (my guess is that they're sending packets out
> regularly).
> 
> We replicated this in our CO and put a hub between the ONT and the Linksys
> CPE so that we could capture those packets.  What we're seeing in that
> capture are directed ARP requests every 7 minutes from the 7609 to the
> Linksys with an ARP response from the Linksys.  After many hours, the 7609-S
> stops sending the ARP requests (well, at least we're not seeing it come in,
> perhaps it did try).  
> 
> We currently have our ARP timeout set to 480 seconds and MAC address table
> aging time to 540 seconds.  Why?  We use "mac-address-table synchronize"
> which is set to 160 seconds by default.  The recommendation from that
> command is to set ARP three times that, so that would be 480.  But it's also
> recommended that the MAC address table aging time be greater than the ARP
> timeout, so we added another 60 seconds on top.
> 
> Two questions: 
> - why is the 7609 sending any directed ARP requests at all, every 7 minutes?
> - why does it appear to stop sending them after many hours?
> 
> I'm all ears if we should be using different expiration values, but the
> numbers I'm using are based on reading a lot of cisco-nsp archives and Cisco
> tech articles.
> 
> Frank
> 
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