about L2MTU

RouterOS General
1

I have two routers:

  • physical RB1100AHx2 RouterOS 6.35.4
  • virtual CHR RouterOS 6.37.1
  1. On both routers I see at least two interfaces (RB1100AHx2 has more, but lets ignore those for now):
    RB11000AHx2
 #     NAME                                TYPE       ACTUAL-MTU L2MTU  MAX-L2MTU MAC-ADDRESS      
 0  RS ether1bond                          ether            1500  1598       9498 12:34:56:78:90:18
 1  RS ether2bond                          ether            1500  1598       9498 12:34:56:78:90:19

CHR

 #     NAME                                TYPE       ACTUAL-MTU L2MTU  MAX-L2MTU MAC-ADDRESS      
 0  RS ether1bond                          ether            1500                  12:34:56:78:90:77
 1  RS ether2bond                          ether            1500                  12:34:56:78:90:79

Question: Why is L2MTU only visible on the RB1100AHx2? Physical capability or driver capability?

  1. I created bonded interfaces using 802.3ad:
    RB11000AHx2
 #     NAME                                TYPE       ACTUAL-MTU L2MTU  MAX-L2MTU MAC-ADDRESS      
 0  RS ether1bond                          ether            1500  1598       9498 12:34:56:78:90:18
 1  RS ether2bond                          ether            1500  1598       9498 12:34:56:78:90:19
 2  R  bond                                bond             1500                  12:34:56:78:90:18

CHR

 #     NAME                                TYPE       ACTUAL-MTU L2MTU  MAX-L2MTU MAC-ADDRESS      
 0  RS ether1bond                          ether            1500                  12:34:56:78:90:77
 1  RS ether2bond                          ether            1500                  12:34:56:78:90:79
 2  R  bond                                bond             1500  1500            12:34:56:78:90:77

Question: Why is L2MTU only visible on the bonded interface on the CHR?

2

Put same version on both devices, there must be some change in changelog that does that.

3

Thanks for your response, I found it.

Version 6.36:
*) bonding - implemented l2mtu value == smallest slave interfaces l2mtu;

Since L2MTU isn’t available on the CHR interfaces, why is L2MTU set on the bonded interfaces?

4

In cases when L2MTU is not supported by the driver L2MTU=MTU, that is why you see 1500 for bonding interface.