LinuxQuestions.org
Share your knowledge at the LQ Wiki.
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 06-26-2016, 07:32 AM   #1
sshaligr
LQ Newbie
 
Registered: Jun 2016
Posts: 3

Rep: Reputation: Disabled
how to loopback between 2 10G ports on the NIC


Hi All,
I have a 82599 based 2 port NIC with SFP+ modules. I am trying to loopback between the 2 ports using a standard SFP+ cable (rx of one port to the tx of the other) without going through a router, i.e. direct connection. the link is down.

i have tried using ethtool to change the autoneg, speed and duplex but it is not taking any effect.
please help.
thanks
sks
 
Old 06-27-2016, 11:19 AM   #2
lazydog
Senior Member
 
Registered: Dec 2003
Location: The Key Stone State
Distribution: CentOS Sabayon and now Gentoo
Posts: 1,249
Blog Entries: 3

Rep: Reputation: 194Reputation: 194
First question is why are you trying to do this?
What benefit are you hoping to achieve doing this?
 
Old 06-28-2016, 08:13 AM   #3
sshaligr
LQ Newbie
 
Registered: Jun 2016
Posts: 3

Original Poster
Rep: Reputation: Disabled
i am trying to tx out packets at high speeds (via tcpreplay) and then have an application receive and parse various protocols from the raw data received on the other port. basically test protocol parsers at high speeds.
 
Old 06-28-2016, 11:17 AM   #4
lazydog
Senior Member
 
Registered: Dec 2003
Location: The Key Stone State
Distribution: CentOS Sabayon and now Gentoo
Posts: 1,249
Blog Entries: 3

Rep: Reputation: 194Reputation: 194
Yeah this isn't going to work. For starters the switch is going to close one of those ports down as it causes a loop. The only way to have 2 nic up on the same switch is to have them bundled together in a port-channel.

As to high speeds you are talking about sending and receiving on the same connection isn't going to change that you are still going to get the same speed.
 
Old 06-30-2016, 06:59 AM   #5
jnihil
Member
 
Registered: Dec 2012
Location: inside the matrix
Distribution: Debian, Xubuntu, Gentoo, Antergos
Posts: 90

Rep: Reputation: 27
sshaligr didn't say anything about connecting to a switch.
There will be no loops if the server with the 2 NICs are simply connected and linked up, no internal bridging.

Are you using a Direct Attach Cable?
Does the link show as UP?
What does the logs say when you bring the interface up?

Last edited by jnihil; 07-01-2016 at 01:54 PM.
 
Old 07-03-2016, 12:51 PM   #6
sshaligr
LQ Newbie
 
Registered: Jun 2016
Posts: 3

Original Poster
Rep: Reputation: Disabled
the interface says it is UP but when i run ethtool -m it says that the link is down.
i think we have narrowed it down to the sfp (there was no light coming out of it).
And yes it is a direct attach without a switch.
we are replacing the sfp. one question - do we absolutely need a direct attach cable or will any cable work ?
 
Old 07-04-2016, 03:42 AM   #7
jnihil
Member
 
Registered: Dec 2012
Location: inside the matrix
Distribution: Debian, Xubuntu, Gentoo, Antergos
Posts: 90

Rep: Reputation: 27
I think you can use any passive cable, but you should verify that with your optics datasheet.
 
  


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
Transmit rate decreases when using both Intel NIC 10G ports hjazz6 Linux - Networking 1 06-05-2012 01:54 PM
help for the NIC loopback test functions dfengui Linux - Networking 1 06-17-2007 06:43 PM
NIC will only loopback on Ubuntu 5.04 TheSerpent Linux - Hardware 8 12-26-2006 05:00 AM
Anyone using LeWiz 10g NIC with TOE .. ngsol Linux - Networking 0 09-12-2006 11:04 AM
nic active, but can't ping beyond loopback pvl Linux - Networking 4 04-01-2004 10:14 AM

LinuxQuestions.org > Forums > Linux Forums > Linux - Networking

All times are GMT -5. The time now is 03:20 AM.

Main Menu
Advertisement
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
Open Source Consulting | Domain Registration