Cell Relay Archive

[V Tharaneedharan <dharani@cisco.com>]

Hi,

> I have some doubt on this subject,
> Suppose I running TCP/IP over LANEv1.
> i) WHat is the relationship between IP address, MAC address and ATM
>  Address.? Would there be 2 ARP table. One for MAC to ATM and one
>  for IP to MAC.

The IP address is mapped to MAC address as it was done in legacy LAN.
LANE is not even aware that such a thing is done. The MAC address is mapped
to ATM address.

So you have two tables:

1. IP to MAC (as with legacy LAN using ARP)

2. MAC to ATM (as LANE defines using LE_ARP, learning etc)

> ii) Suppose an IP host A1 ( empty cache , have not make an connection
> yet)
>   start to ping a host (a  server  e.g.). on the same ELAN.
>  How will the process goes about?
>  Will the IP host A1 send a broadcast MAC to the BUS first.?

Consider the following layers:

	----------------
	       IP
	----------------
	       MAC
	----------------
	      LEC
	----------------
	 ATM Signalling
	----------------
	       ATM
	----------------

	1. Now ping in host A1, leads to sending an IP packet. 
	2. IP has a IP to MAC (ARP) table in which it does not find a 
		MAC address for server IP say S1. 
	3. So it sends an ARP request with broadcast MAC address
		as the destination address. LEC sees that and sends it through 
		the Multicast send VCC to the BUS.
	4. BUS sends it to all the LECs in the ELAN.
	5. All the clients pick it up but ARP server of one client
		finds that someone is asking for his MAC address, so
		it coins ARP response and sends it down
		(this guy knows the MAC address of A1, so it
		uses unicast MAC address as destination instead of broadcast MAC address)
	6. Now LEC sees this packet and finds that it has to go to
		a particular client. If it has MAC-to-ATM address details
		in his LE_ARP table, and the connection is available (Data Direct VCC),
		then it sends the reply to him directly. Else it sends the ARP
		Response through the BUS itself. Note that a similar action
		like the one given in step 9 and 10 may also take place.

	7. Now the host A1 gets the ARP Response and IP-to-MAC relationship
		is established for the destination address.
	8. Host A1 sends down the data packet with the now obtained destination MAC address.

	9. LEC sees the MAC address and looks up if it has it in its local
		LE_ARP table to see if MAC-to-ATM relationship details exist
		for this MAC address. If the relationship exists and a connection
		(Data Direct VCC) also exists, then it puts the packet to that
		VCC.

	10. Else it sends the packet to the BUS. The BUS sends the packet to all
		the clients so that the actual client picks it up while all
		others ignore the packet.

	11. If there is no Data Direct VCC available but the table has MAC-to-ATM 
		relationship, then it starts the process of establishing the connection.

	10. Now if the MAC-to-ATM relationship doesnot exist in the local LE_ARP table,
		then it consults the LE Server by sending LE_ARP_REQUEST asking
		the ATM address for the destination MAC address. The LE Server
		gives the relationship (either it has in its LE_ARP table
		or it gets the details from the destination client by forwarding
		the LE_ARP_REQUEST (What is the ATM address of this MAC address?)
		and getting the LE_ARP_RESPONSE (This is the ATM Address for the
		MAC Address) sent either by the client or by a proxy client). 
		Then the client of S1 starts the process of establishing the connection.

	For simplicity, I have not mentioned the other possibilities. But I hope
	this answers your question.

Regards
dharani

M V Tharaneedharan
Wipro Limited
R&D, Cupertino, CA