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Collisions and deferred on gigabit port? how?

Posted: Thu Oct 10, 2019 3:04 am
by millenium7
Riddle me this

name="ether1"
tx-packet=57 236 390
tx-64=996 840
tx-65-127=7 610 302
tx-128-255=49 379 966
tx-256-511=273 234
tx-512-1023=493 835
tx-1024-1518=15 100
tx-broadcast=559 491
tx-pause=0
tx-multicast=973 397
tx-collision=180
tx-excessive-collision=0
tx-multiple-collision=28
tx-single-collision=92
tx-deferred=77 937
tx-late-collision=62
tx-drop=62
tx-fcs-error=0

How do you get collisions on a gigabit port since it only operates in full duplex? and why so many deferred packets?
This connects directly to a PMP450 radio, nothing in between

I'm thinking either faulty radio or router

Re: Collisions and deferred on gigabit port? how?

Posted: Thu Oct 10, 2019 9:00 am
by mkx
How do you get collisions on a gigabit port since it only operates in full duplex?

My RBD52G (giga ethernet ports) shows this:
/interface ethernet> monitor ether1 
                      name: ether1
                    status: link-ok
          auto-negotiation: done
                      rate: 1Gbps
               full-duplex: yes
           tx-flow-control: no
           rx-flow-control: no
               advertising: 10M-half,10M-full,100M-half,100M-full,1000M-half,
                            1000M-full
  link-partner-advertising: 10M-half,10M-full,100M-half,100M-full,1000M-half,
                            1000M-full
Note 1000M-half in the list of advertised (own and link-partner) link modes. Meaning that Gbps ethernet can operate half-duplex and thus collisions can happen.

Re: Collisions and deferred on gigabit port? how?

Posted: Mon Oct 14, 2019 8:47 am
by millenium7
the gigabit standard is full duplex. It may be possible to force it on a MikroTik but thats not the case therefore it should always 'fall back' to full duplex if the other side isn't explicitly asking to do half duplex. The opposite of what ethernet/fast ethernet is

Either way, it's reporting full duplex on both sides of the link

Re: Collisions and deferred on gigabit port? how?

Posted: Mon Oct 14, 2019 11:32 am
by mkx
the gigabit standard is full duplex.

BTW, the link partner in example posted in my previous post is not Mikrotik ...

The IEEE 802.3ab standard defines both half duplex and full duplex. And standard explicitly states that Gbps operation without auto negotiation successfully completed should not be possible (so "fallback" to 1Gbps FD is not acceptable at all). All the rest is implementation dependent (including forced speed and duplex) and might or might not work across different vendors as link partners.