Brownian motion

around the essentials…


REORDER_HDR, again and again

If you wish to use vlan sub-interfaces in linux, and sub-sub-interfaces, and sub-sub-sub-… and if you wish to ping something — sure, you may wish to have them only for switching, but if you wish to ping — don’t forget to re-set REORDER_HDR flag:

ip link set up dev eth2
vconfig add eth2 100
ip link set up dev vlan100
vconfig set_flag vlan100 1 0
vconfig add vlan100 200
ip link set up dev vlan200
vconfig set_flag vlan200 1 0
# ....etc-etc
vconfig add vlan800 900
ip link set up dev vlan900
vconfig set_flag vlan900 1 0
ip add add brd dev vlan900

Note using command vconfig set_flag DEV 1 0 — i mean exactly this :-)

Now (since 2.6.x?.. can’t remember, doesn’t matter) Linux kernel creates vlan interfaces with REORDER_HDR=1.

You can verify current value of REORDER_HDR flag with command like this:

# cat /proc/net/vlan/vlan900
vlan900  VID: 900	 REORDER_HDR: 0  dev->priv_flags: 1
         total frames received          172
          total bytes received       222546
      Broadcast/Multicast Rcvd            0

      total frames transmitted          405
       total bytes transmitted       283743
            total headroom inc            0
           total encap on xmit           26
Device: vlan900
INGRESS priority mappings: 0:0  1:0  2:0  3:0  4:0  5:0  6:0 7:0
 EGRESS priority mappings: 
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