Is it safe to change interface MAC address?

Post new topic   Reply to topic    DD-WRT Forum Index -> Broadcom SoC based Hardware
Author Message
Duxa
DD-WRT User


Joined: 16 Aug 2013
Posts: 191

PostPosted: Tue Jun 14, 2022 23:43    Post subject: Is it safe to change interface MAC address? Reply with quote
Hi all, trying to debug this pesky message:

br0: received packet on eth1 with own address as source address

Some of my interfaces have the same MAC, I want to change them. Is it safe to do so assuming there wont be collisions with another device on network?
Sponsor
dale_gribble39
DD-WRT Guru


Joined: 11 Jun 2022
Posts: 1900

PostPosted: Wed Jun 15, 2022 2:43    Post subject: Reply with quote
I believe that log message is related to a loopback present on your LAN and is related to WAN NAT redirection. In looking for discussion about this log message, I found the following forum threads:

https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=153395
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=283014
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=314572
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=318441
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=326851

I also looked up WAN NAT redirection and found these:

https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=74107
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=84043
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=85841
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=89353
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=153289
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=311868
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=328862
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=330285
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=331859

In regards to the MAC address situation, on which particular interfaces is the MAC address the same? I relented to not copying and pasting any threads returned by this search:

https://www.google.com/search?q=mac+address+identical+on+more+than+one+interface+dd-wrt+site%3Aforum.dd-wrt.com

_________________
"The woods are lovely, dark and deep,
But I have promises to keep,
And miles to go before I sleep,
And miles to go before I sleep." - Robert Frost

"I am one of the noticeable ones - notice me" - Dale Frances McKenzie Bozzio

<fact>code knows no gender</fact>

This is me, knowing I've ruffled your feathers, and not giving a ****
Some people are still hard-headed.

--------------------------------------
Mac Pro (Mid 2012) - Two 2.4GHz 6-Core Intel Xeon E5645 processors 64GB 1333MHz DDR3 ECC SDRAM OpenSUSE Leap 15.5
the-joker
DD-WRT Developer/Maintainer


Joined: 31 Jul 2021
Posts: 2146
Location: All over YOUR webs

PostPosted: Wed Jun 15, 2022 6:59    Post subject: Reply with quote
You can safely ignore that message, br0 is a bridge, bridges are aggregates of several interfaces (into a single interface in this case br0), by default br0 has several interfaces aggregated so it will happen, but its not a concern.

If you want to check the current MAC addresses, navigate to Setup tab -> Networking tab and you can see what interfaces are aggregated into br0 and the corresponding MAC addresses further down on that page that correspond to these interfaces.

If you look carefully some of those interfaces will have the same MAC address, ill let you figure out why, check any matching MAC's against eth1.

Also you dont mention your DD-WRT version or your router brand+version, I don't recommend messing around in the networking tab with old DD-WRT builds and on specific platforms by using the networking tab to change MAC addresses, I know from a good authority this needs testing and may not be fully implemented in all platforms.

Be warned and prepared.

I have on my Broadcom RT-AC68U and done changed all interfaces to unique fake MAC addresses (but you need to know how to create valid fake MAC's between 00 and FF, bits need to end in a and I dont have any such messages, so you know.

_________________
Saving your retinas from the burn!🔥
DD-WRT Inspired themes for routers
DD-WRT Inspired themes for the phpBB Forum
DD-WRT Inspired themes for the SVN Trac & FTP site
Join in for a chat @ #style_it_themes_public:matrix.org or #style_it_themes:discord

DD-WRT UI Themes Bug Reporting and Discussion thread

Router: ANus RT-AC68U E1 (recognized as C1)
the-joker
DD-WRT Developer/Maintainer


Joined: 31 Jul 2021
Posts: 2146
Location: All over YOUR webs

PostPosted: Sun Jul 03, 2022 10:57    Post subject: Reply with quote
Reports on build threads are ignored regarding this subject because, it's not a bug or issue, it's simply working as how it is setup per default or non default configs where MAC addresses maybe duplicated on various interfaces and all are aggregated under the same bridge.

Understand what a bridge is and how it works, routers have 1 MAC address per unique wifi radio, 1 mac address for the switch (some routers have more physical interfaces so more unique MACs e.g. R9000 has 2 switches). So there is a limited set of physical interfaces with unique MAC addresses to begin.

Then enter virtual lan interfaces or virtual ap's these all need a mac address
you have a switch with 4 lan ports and 1 wan port and the r7000 only has 3 real unique mac addresses 1 per radio 1 for switch = 3 if my math is correct.

Related
1) https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=314572
2) https://svn.dd-wrt.com/ticket/3998 (has more threads in forums about this

Semi explanation: https://forum.dd-wrt.com/forum/viewtopic.php?p=1264843#1264843

It is safe to set your own unique MAC addresses to resolve the annoying messages since all aggregated interfaces on the bridge some may have duplicated mac addresses and hence this will happen.

Several ways to solve exist depending on your setup, but simplest IMO is to assign unique MACs to each interface be that physical or virtual.

_________________
Saving your retinas from the burn!🔥
DD-WRT Inspired themes for routers
DD-WRT Inspired themes for the phpBB Forum
DD-WRT Inspired themes for the SVN Trac & FTP site
Join in for a chat @ #style_it_themes_public:matrix.org or #style_it_themes:discord

DD-WRT UI Themes Bug Reporting and Discussion thread

Router: ANus RT-AC68U E1 (recognized as C1)
Duxa
DD-WRT User


Joined: 16 Aug 2013
Posts: 191

PostPosted: Sun Jul 03, 2022 20:49    Post subject: Reply with quote
the-joker wrote:
Reports on build threads are ignored regarding this subject because, it's not a bug or issue, it's simply working as how it is setup per default or non default configs where MAC addresses maybe duplicated on various interfaces and all are aggregated under the same bridge.

Understand what a bridge is and how it works, routers have 1 MAC address per unique wifi radio, 1 mac address for the switch (some routers have more physical interfaces so more unique MACs e.g. R9000 has 2 switches). So there is a limited set of physical interfaces with unique MAC addresses to begin.

Then enter virtual lan interfaces or virtual ap's these all need a mac address
you have a switch with 4 lan ports and 1 wan port and the r7000 only has 3 real unique mac addresses 1 per radio 1 for switch = 3 if my math is correct.

Related
1) https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=314572
2) https://svn.dd-wrt.com/ticket/3998 (has more threads in forums about this

Semi explanation: https://forum.dd-wrt.com/forum/viewtopic.php?p=1264843#1264843

It is safe to set your own unique MAC addresses to resolve the annoying messages since all aggregated interfaces on the bridge some may have duplicated mac addresses and hence this will happen.

Several ways to solve exist depending on your setup, but simplest IMO is to assign unique MACs to each interface be that physical or virtual.


The problem is that even with unique MAC addresses the error messages are there. It seems to be related to wireless. As I get a message every few minutes, if I turn off wifi completely (both radios) then there are no messages at all (tested for many hours).

Now to make things a bit worse, with last build new message started appearing (no change in config):

Code:
eth1: Bad address
the-joker
DD-WRT Developer/Maintainer


Joined: 31 Jul 2021
Posts: 2146
Location: All over YOUR webs

PostPosted: Thu Jul 07, 2022 10:05    Post subject: Reply with quote
Well, I can say with certainty that modding the MAC addresses here assigning unique MACs made that message go away.

I only have br0 and two unbridged VAPS, the interfaces aggregated under br0 all have unique MACs on my setup and those messages are gone.

MAC Cloning WAN side has a unique MAC now which is vlan2 for both R7000 and my RT-AC68U

vlan2 has a unique MAC assigned.
vlan1 has a unique MAC assigned.
eth1 is the 2.4 Ghz radio the PHY is AKA wl0 - I also have assigned a different MAC here
eth2 is the 5 Ghz radio the PHY is AKA wl1 - I also have assigned a different MAC here
br0 also has a unique MAC assigned.

Both my VAPs wl0.1 adn wl1.1 have Unique MACs assigned but they are unbridged.

re: [eth1: bad address] message

I think that message maybe goes back to some other issue unrelated to the previous messages in discussion, I cant find the thread now, but you can confirm by running;
Code:
stopservice nas; wlanconf br0 down; wlconf eth0 down; wlconf eth1 down; wlconf eth2 down; startservice nas; wlanconf br0 up; wlconf eth0 up; wlconf eth1 up; wlconf eth2 up

Then scroll up to see if you have same message there which indicates this where the MACs are concerned.

Code:
base addr xx:xx:xx:xx:xx:A4
local bit addr xx:xx:xx:xx:xx:A4
eth2: Bad address


So this is part of the other old issue. Its non critical and can be ignored, its just annoying all these messages are annoying but non critical and wont likely get fixed because they are non critical. However patches are welcome.

If you have other setup, then share screenshots and obviously feel free to gray out the MACs



Capture.PNG
 Description:
 Filesize:  19.49 KB
 Viewed:  1474 Time(s)

Capture.PNG



_________________
Saving your retinas from the burn!🔥
DD-WRT Inspired themes for routers
DD-WRT Inspired themes for the phpBB Forum
DD-WRT Inspired themes for the SVN Trac & FTP site
Join in for a chat @ #style_it_themes_public:matrix.org or #style_it_themes:discord

DD-WRT UI Themes Bug Reporting and Discussion thread

Router: ANus RT-AC68U E1 (recognized as C1)
Mile-Lile
DD-WRT Guru


Joined: 24 Feb 2013
Posts: 1634
Location: Belgrade

PostPosted: Thu Jul 07, 2022 10:26    Post subject: Reply with quote
If someone needs

Online MAC generator
Display posts from previous:    Page 1 of 1
Post new topic   Reply to topic    DD-WRT Forum Index -> Broadcom SoC based Hardware All times are GMT

Navigation

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You can attach files in this forum
You can download files in this forum