LinuxQuestions.org
Help answer threads with 0 replies.
Go Back   LinuxQuestions.org > Forums > Linux Forums > Linux - Networking
User Name
Password
Linux - Networking This forum is for any issue related to networks or networking.
Routing, network cards, OSI, etc. Anything is fair game.

Notices

Reply
 
Search this Thread
Old 03-18-2013, 03:04 AM   #1
madix
LQ Newbie
 
Registered: Feb 2013
Location: bangalore
Posts: 8

Rep: Reputation: Disabled
g-arp not updating mac address


Hi,

I am having multiple PCs receiving a g-arp request from a server. Sometimes, one these PCs does not process the g-arp request and keep sending message to Old Mac address of the server until it itself timeout and send a g-arp request to get updated about the server Mac. I am using CentOs. I don't see kernel also processing the g-arp(I keep certain debug msgs to see if kernel itself is dropping the request).

Pls let me know how to sort it out. I wondered all across internet and didn't find much info.
 
Old 03-20-2013, 12:41 PM   #2
jnihil
Member
 
Registered: Dec 2012
Distribution: Debian, Xubuntu, Gentoo, CentOS, Bhodi
Posts: 47

Rep: Reputation: 2
The kernel doc says that GARPs are accepted if the IP entry already exists in the ARP cache:

(from https://www.kernel.org/doc/Documenta...p-sysctl.txt):

arp_accept - BOOLEAN
Define behavior for gratuitous ARP frames who's IP is not
already present in the ARP table:
0 - don't create new entries in the ARP table
1 - create new entries in the ARP table

Both replies and requests type gratuitous arp will trigger the
ARP table to be updated, if this setting is on.

If the ARP table already contains the IP address of the
gratuitous arp frame, the arp table will be updated regardless
if this setting is on or off.



Are you running a really old kernel version?
 
Old 03-20-2013, 04:41 PM   #3
jefro
Guru
 
Registered: Mar 2008
Posts: 11,714

Rep: Reputation: 1439Reputation: 1439Reputation: 1439Reputation: 1439Reputation: 1439Reputation: 1439Reputation: 1439Reputation: 1439Reputation: 1439Reputation: 1439
Is there a static arp entry on this one PC?
 
Old 03-20-2013, 11:14 PM   #4
madix
LQ Newbie
 
Registered: Feb 2013
Location: bangalore
Posts: 8

Original Poster
Rep: Reputation: Disabled
Quote:
Originally Posted by jefro View Post
Is there a static arp entry on this one PC?
No, there is NO static arp entry. Everything gets updated dynamically either with self arp request or a g arp from the other side.
 
Old 03-20-2013, 11:21 PM   #5
madix
LQ Newbie
 
Registered: Feb 2013
Location: bangalore
Posts: 8

Original Poster
Rep: Reputation: Disabled
Quote:
Originally Posted by jnihil View Post
The kernel doc says that GARPs are accepted if the IP entry already exists in the ARP cache:

(from https://www.kernel.org/doc/Documenta...p-sysctl.txt):

arp_accept - BOOLEAN
Define behavior for gratuitous ARP frames who's IP is not
already present in the ARP table:
0 - don't create new entries in the ARP table
1 - create new entries in the ARP table

Both replies and requests type gratuitous arp will trigger the
ARP table to be updated, if this setting is on.

If the ARP table already contains the IP address of the
gratuitous arp frame, the arp table will be updated regardless
if this setting is on or off.



Are you running a really old kernel version?
I actually tried this by setting arp_accept to 1. I think still faced the issue. My understanding about arp_accept is that setting this will may result in frequent arp cache overflow due to accepting every other g-arp request that is coming in the n/w. I want the update to happen only for my server.

I am using linux-2.6.18 kernel version.
 
Old 03-21-2013, 08:23 AM   #6
jnihil
Member
 
Registered: Dec 2012
Distribution: Debian, Xubuntu, Gentoo, CentOS, Bhodi
Posts: 47

Rep: Reputation: 2
'arp cache overflow'?

how did to come this conclusion?
 
Old 03-26-2013, 12:16 PM   #7
madix
LQ Newbie
 
Registered: Feb 2013
Location: bangalore
Posts: 8

Original Poster
Rep: Reputation: Disabled
Quote:
Originally Posted by jnihil View Post
'arp cache overflow'?

how did to come this conclusion?
I could be wrong!
I meant the cache may get into thrashing due to frequent updates... Anyways I got the problem solved by clearing the cache in a given time...
 
  


Reply


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
same MAC address for different IP addresses in ARP response VinodVandkar Linux - Networking 5 01-25-2013 04:32 PM
using arp for converting ip address to mac address in kernel module programing in c karan2386 Linux - Kernel 1 03-31-2012 05:02 AM
[SOLVED] ARP does not resolve MAC address of hosts on the same subnet chenbo Linux - Networking 1 07-26-2011 10:12 PM


All times are GMT -5. The time now is 10:54 PM.

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