1. In the scenario when a g/w is defined and the destination is not the local
subnet, there is an ARP request with the targeted IP for the gateway &
destination as the remote subnet IP.
I am still not clear about :
2. In the scenario where there is no g/w defined. How would the proxy ARP work?
if there is no arp req with the targeted IP as the destination IP.
"Morris, Jason L." <[EMAIL PROTECTED]> wrote: v\:*
{behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:*
{behavior:url(#default#VML);} .shape {behavior:url(#default#VML);}
You only do ARP discovery for hosts in your local subnet. Youll do an ARP
discovery for your gateway but not the far in end host address. The only time
Ive seen proxy arp come into play is when you either have a subnet split by a
router (poopy) or you have a miss configured subnet mask on a host, then that
host will do ARP discovery requests for hosts on the lan, the box running proxy
arp sees this, recognizes that its not on that lan and responds with its own
MAC and then routes the traffic as it normally would.
Anyway Im rambling, I think the short answer is the sending host doesnt
send out an arp request with an L3 destination address of the far side, it
sends an arp request with an L3 destination address of its default gateway.
Someone out there can correct me if Im off base on something.
Jason Morris
---------------------------------
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ajay Chenampara
Sent: Tuesday, February 19, 2008 6:24 AM
To: [email protected]
Subject: [OSL | CCIE_RS] very basic ARP question
If we have two interfaces connected to the the same VLAN (or even using a
cross connect) and if we assign addresses that belong to different subnets,
they cannot ping each other. I need help in understanding why.
My understanding is that when a packet is flowing down the OSI layers, based
on the IP and subnet, it understands whether the destination is in the local
subnet or not (if local, lookup the local arp cache, if not in the cache send
an ARP request b/c).
This ARP req - which is b/c - does not contain mask info. Only the
destination IP and source IP. So typically, a g/w will respond with it's MAC if
it has a route to the destination (and if proxy arp is configured). What if
the destination is another host physically connected to the source (same VLAN
or cross connect). It should see the ARP request, decapsulate it to L3, find
that the packet is destined for it. So why cant they communicate????
---------------------------------
Never miss a thing. Make Yahoo your homepage.
---------------------------------
Looking for last minute shopping deals? Find them fast with Yahoo! Search.
