[j-nsp] Weird ARP issue

[Luca Salvatore]

Not sure I understand....

The originating host will ARP for his gateway.
Then the traffic will be routed to destination.  The router at the end will then ARP for the end host on the local subnet, otherwise how would the router know which port to send the traffic to.

Luca


-----Original Message-----
From: Chris Cappuccio [mailto:chris at nmedia.net] 
Sent: Thursday, 31 January 2013 3:17 PM
To: Luca Salvatore
Cc: Payam Chychi; juniper-nsp at puck.nether.net
Subject: Re: [j-nsp] Weird ARP issue

Luca Salvatore [Luca at ninefold.com] wrote:
> I Haven???t touched any ARP config, it???s just the defaults.
> 
> The plot thickens:
> 
> I did some port-mirroring, when I send traffic on port 80 to the VM the switch will generate an Arp request.
> Same if I do a ping, I see an ARP request.
> 
> However for SSH traffic, the switch never generates an ARP request so the traffic never gets to the end host.
> 

The ARP request is initiated by the end host, not the switch. The switch passes it. The switch can't tell if the ARP request is initiated by the SSH, PING, or any other request. Of course, the ping generates an ARP request, then the host routing table no longer needs to do a second ARP request for the SSH session, which would explain what you see (if you aren't deleting the arp table entry on the end host between
tests)