Hello Subashini,
ARP is located in the LL and does the translation between the IP address of
the sender node and the MAC address of the destination node.So when a packet
arrives at the LL and is searching for the next hop to be rooted,ARP does the
mapping between the IP address of the sender node and the MAC address of the
destination node.This mapping occurs after a search at an ARP table that its
node holds.If the mapping that you want does not exist in the ARP table then an
ARP QUERY broadcast packet is being sent to all the other nodes asking which
node has the appropriate MAC address.The node which has this MAC address
replies with a unicast ARP reply packet.Then the sending node knows exactly
where to send his packet.
As far as i know for ns-2.27 the buffer that keeps the packets which wait for
this address translation has limited space.Also when a second packet arrives
which has the same IP address as the previous one,already waiting in the queue,
then this packet is discarded.That´s why you get an ARP IFQ drop.
Look at chapter 16 page 150 of the ns-manual for further details
Moreover, as far as i know there is not a time-out scheme implemented in ns
for the packets waiting in the ARP queue.Also there is not a retry scheme
implemented.That is, if an ARP reply packet doesn´t make it,a second ARP
query packet is not being sent.The above seem to me weird.
If something of the above is incorrect i would like to hear a second opinion
about them
regards,
Michael
Subashini S <[EMAIL PROTECTED]> έγραψε:
H,
I have modified AODV algorithm for wireless networks.
The send request routine is working fine. The node is able to receive the
request and it also generates the reply packet.
But the reply packet is getting dropped and the reason i found from the
trace file was that
D -2- IFQ ARP 0 TAODV 68 [0 0 2 800] [2:255 1:255 3 0 0] [ 0x4 1 [2
8] 10.00] REPLY
TAODV is the name of the packet and TAODV_RREP=4
I would like to know the meaning of IFQ and ARP. Is it due to some timeout
or congestion? if so which timeout does this mean? how do i rectify it.?
And i also get
null() : calling drop()
Is this due to the TTL of the packet?
Please help me out.
Thanks a lot,
Subashini
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