From my own experience with arp.cc, this explanation is entirely correct, especially the part where the buffer only has space for 1 packet
> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf > Of Michael Sidiropoulos > Sent: terça-feira, 7 de Março de 2006 16:23 > To: Subashini S > Cc: ns-users@ISI.EDU > Subject: Re: [ns] Urgent: Meaning of ARP IFQ in trace file > > > 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 > > > > > > > > --------------------------------- > Χρησιμοποιείτε Yahoo! > Βαρεθήκατε τα ενοχλητικά μηνύ ματα (spam); Το Yahoo! Mail διαθέτει την > καλύτερη δυνατή προστασία κατά των ενοχλητικών μηνυμάτων > http://login.yahoo.com/config/mail?.intl=gr
