802.1 Q in Q and ping latency

RouterOS General
1

Here you can see my situation:
sVlan_cVlan.jpg
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It’s a simple implementation of Q in Q with a c-vlan inserted into a s-vlan realized by bridges in a hyperlan transport network.
Routers/bridges are mikrotik RB750UP and RB450G and radios are ubiquiti stuff with L2MTU set to 2024.
This network works: you can ping from c-vlan IP1 to c-vlan IP2 with 1500 bytes packets without fragmentation.
The problem is latency:
Average of 20 1500bytes pings results (don’t fragment):

  1. from Hyperlan IP1 to Hyperlan IP2: 9ms ;
  2. from S-VLAN IP1 to S-VLAN IP2: 12ms ;
  3. from C-VLAN IP1 to C-VLAN IP2: 35ms ;
    Average of 20 30000bytes pings results :
  4. from Hyperlan IP1 to Hyperlan IP2: 170ms ;
  5. from S-VLAN IP1 to S-VLAN IP2: 117ms ;
  6. from C-VLAN IP1 to C-VLAN IP2: 117ms ;

As you can see, with 30k icmp packets (fragmented in 20 1500B, of course) you have the same latency in c-vlan and s-vlan, but more latency in direct eth IP pings;
With 1500B icmp packets the situation is much more different: s-vlan latency similar to direct eth one, c-vlan latency about 3x slow!
Why?
Using packet sniffer on eth interface you have always 1522 bytes packets (1508 + 14 eth), as with single 1500B pings that with 30k pings.

2

Did you ever get a solution to this ?

3

I find that the major issue is for “airmax” ubiquiti tdma protocol.
Now I use all remaining ubiquiti stuff in 802.11 mode and I started using new mikrotik devices.
In this way the high latency in tunnels can be avoided.