Share your knowledge at the LQ Wiki.
Go Back > Forums > Linux Forums > Linux - Newbie
User Name
Linux - Newbie This Linux forum is for members that are new to Linux.
Just starting out and have a question? If it is not in the man pages or the how-to's this is the place!


  Search this Thread
Old 02-27-2006, 02:26 PM   #1
LQ Newbie
Registered: Feb 2006
Posts: 2

Rep: Reputation: 0
Query of ArpCache is not spawning ARP Request

NOTE: I am posting this on "newbie" (instead of "networking",...) so as to influence the level of the response. I am a new developer on Linux, and will likely need more detailed response. Thank-you, in advance, for your patience.

MODERATOR: Feel free to move this thread to another forum, if you feel that I can get the lower-level response there as well.

BACKGROUND: I am running MonteVista Linux on custom hardware, using a PowerPC (core within Xilinx FPGA). I have some initialization code in a daemon that queries the ARP cache for an entry associated with my default Gateway's IP address. I am using an ioctl(fd,SIOCGARP) call for this query. As expected, the initial several attempts return an error; but in most cases, a later attempt returns the ARP cache entry (assuming that the Gateway responds). From what I have read, the initial attempt returns the error, because no cache entry initially exists; but then it generates an ARP Request out the Ethernet interface, to cause the entry to be created. The intermediate error responses will continue to occur while the stack is waiting for the ARP Reply. In a normal case, I can see these ARP Request/Reply messages in a sniffer trace.

FAILURE CASE: In some (infrequent) cases, the Linux code never generates an ARP Request, even if the hardware and other conditions are the same (as the normal case). I can confirm that no ARP Requests are being sent, both by a sniffer trace and a TCPDUMP of the interface. At times, the failure case seems to be avoided if the stack receives frames (e.g., broadcasts, from external source) before I query the ARP cache.

1) What can cause the Linux stack to not generate ARP Requests when I query the ARP cache?
2) Is there anything I can monitor to provide more operational information about what it is doing, and why?
3) Is there a way I can force it to generate the ARP Request for this scenario?


<<< vern >>>


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Strange ARP behavior : A linux server responds to all ARP requests Hdvd21 Linux - Networking 4 10-24-2013 05:02 AM
sending an arp request jagman Programming 2 02-27-2006 02:59 PM
ARP request davidho3 Linux - Networking 1 11-06-2004 09:48 AM
ARP request davidho3 Linux - Networking 2 11-05-2004 10:01 AM
Disabling ARP probes after receiving an ARP request AltecLansingMan Linux - Networking 1 03-30-2004 01:25 PM > Forums > Linux Forums > Linux - Newbie

All times are GMT -5. The time now is 04:41 AM.

Main Menu
Write for LQ is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration