Subject: Re: [vserver] ping vs. IP address vs. MAC (address)
From: "John A. Sullivan III" <jsullivan@opensourcedevel.com>
Date: Fri, 01 May 2009 12:38:19 -0400

On Fri, 2009-05-01 at 09:27 -0700, Roderick A. Anderson wrote:
> Michael S. Zick wrote:
> > On Fri May 1 2009, Martin wrote:
> >> On Fri, 2009-05-01 at 08:54 -0700, Roderick A. Anderson wrote:
> >>> I'm asking for a clue stick here.  First time I've run into this issue 
> >>> ... hard.  Be a few times where it took a bit for outbound traffic to 
> >>> get a route but can't remember running into this problem.
> >>>
> >>> The short question is: does the network/NIC _know_ which IP address it 
> >>> is responding for when a ping request comes in or does it just respond 
> >>> to the ping request at the MAC (hardware?) level?
> >>>
> > 
> > The *NIC* responds to MAC address(es) -
> > The *network* - now that is a big question.  ;)
> 
> So if a ping request comes in the NIC it should respond regardless of 
> what IP it was sent to.  That makes sense.
The NIC will respond but the IP stack will not
> 
> > 
> > There is a ARP cache in the kernel, but it *should* be rather short-lived.
> > Try arpping to help find out what is happening.
> 
> Oddest stuff happening.  When I check the arp table on the old host the 
> troublesome guest's name (not IP) doesn't show up.  When I ping the 
> guest from another system the entry shows up.
> 
> I was thinking the main router, between the two hosts, is using a long 
> lived arp cache.
I have seen routers hold onto ARP cache for a very long time.
> 
> I prefer staying way from it, the router, but may have to get access and 
> take a look around.  Maybe flush the arp cache, if I can, right after 
> shutting down the old guest and starting the new.
> 
> Thanks for the ideas.
> 
> 
> \\||/
> Rod
-- 
John A. Sullivan III
Open Source Development Corporation
+1 207-985-7880
jsullivan@opensourcedevel.com

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