buglwIP - A Lightweight TCP/IP stack - Bugs: bug #54700, Unexpected expiry of pending ARP...

 
 

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bug #54700: Unexpected expiry of pending ARP table entry

Submitter:  Florent Matignon <fmatignon>
Submitted:  Thu 20 Sep 2018 04:40:34 PM UTC
   
 
Category:  ARP Severity:  3 - Normal
Item Group:  Change Request Status:  Fixed
Privacy:  Public Assigned to:  goldsimon
Open/Closed:  Closed Planned Release:  None
lwIP version:  git head

Fri 01 Oct 2021 06:32:42 PM UTC, comment #3: 

Yes, I've picked it for 2.1.3

Simon Goldschmidt <goldsimon>
Group administrator
Wed 29 Sep 2021 02:37:50 AM UTC, comment #2: 

This fix (commit ffbe075d5623 "bug #54700: Unexpected expiry of pending ARP table entry") seems the material for v2.1.3.

Axel Lin <axellin>
Group Member
Fri 26 Oct 2018 06:59:42 PM UTC, comment #1: 

Pushed, thanks for the patch.

Simon Goldschmidt <goldsimon>
Group administrator
Thu 20 Sep 2018 04:40:34 PM UTC, original submission:  

Hi,

In current etharp implementation, the ctime field of an ARP table entry is reset when an empty entry is selected for a given address.

This can create situations where an ARP table entry can expire even if the application (any upper layer) has initiated an ARP query immediately before.
Once the entry has expired, it could be recycled for another address and then the ARP reply corresponding to the request previously sent could be dropped if there are no more available empty entry in the table.
(see attached commented debug log for a more concrete example)

A suggestion to avoid such a situation would be to reset the ctime field each time the application explicitely request an ARP resolution with etharp_query().
(see attached patch)

I couldn't find any reference document on ARP table management (and specifically on pending entry management).
Do you see any drawback or problem with this suggestion?

Thanks!

Florent Matignon <fmatignon>

 

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Attached Files
file #45063:  debug.txt added by fmatignon (1KiB - text/plain)

 

Depends on the following items: None found

Items that depend on this one: None found

 

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    Follow 5 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2018-10-26 goldsimon StatusNone Fixed
        Assigned toNone goldsimon
        Open/ClosedOpen Closed
    2018-09-20 fmatignon Attached File- Added etharp-early-table-entry-expiry.patch, #45062
        Attached File- Added debug.txt, #45063

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