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georgekaskader
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Joined: Wed Sep 11, 2019 5:26 pm

VPLS MTU and interface errors RX-Too-long statistics

Wed Apr 07, 2021 12:54 pm

Hi Team,

I Have a problem with I guess MTU while configuring VPLS for PPPOE in my site.
My site is mostly wireless devices like Dynadish, Omnitik AC etc 95% MikroTik.
On some devices I can find in interface statistics errors which points to:
Rx Too Long
Here is my map for example VPLS path where I can find RX TOO LONG errors:
RB4011(BONDING)<sfp1-sfp1>POWERBOX<eth3-eth1>LHG60<->LHG60 | BACKUP IS REALIZED BY UBIQUITI AC<->HAPAC2(BONDING)<-> WIRELESS NETWORK FULL MIKROTIK <->OMNITIK AC
There are 2 vlans bounded to Bonding IF, to realize active backup if 60GHZ gets disconnected, between RB4011 and HAPAC2 and it works correctly.
OSPF and LDP session are UP, Loopbacks are reachable.
The VPLS tunnel is between first and last device. On every device physical interface L2 MTU is set to MAXIMUM (min. 2028B on wireless).

Every device accross VPLS tunnel path has config:
ETHERNET/WIRELESS IF:
L3MTU=1500
L2MTU= =>2028
MPLS IF MTU=1600

Here is my config for RB4011 PPPoE server which is central VPLS concentrator:
IP
-------------
address=172.35.128.1 interface=Loopback_OSPF network=172.35.128.1

MPLS CONFIG
-------------
/mpls interface
set [ find default=yes ] mpls-mtu=1600
/mpls ldp
set enabled=yes loop-detect=yes lsr-id=172.35.128.1 transport-address=172.35.128.1
/mpls ldp accept-filter
add prefix=172.35.128.0/23 <- Loopback IP
add prefix=172.16.128.0/23 <- Loopback IP
add accept=no
/mpls ldp advertise-filter
add prefix=172.35.128.0/23 <- Loopback IP
add prefix=172.16.128.0/23 <- Loopback IP
add advertise=no
/mpls ldp interface
add interface="BONDING DO SKR"

PHYSICAL IF
-------------
name="sfp-sfpplus1" mtu=1500 l2mtu=9586 <- physical IF

LOGICAL IF
-------------
name="BONDING DO SKR" mtu=1500 l2mtu=9582
slaves=vlan-100_DO_SKR_LAG-1_sfp1,vlan-200_DO_SKR_LAG-2_sfp1 mode=active-backup primary=vlan-100_DO_SKR_LAG-1_sfp1 <- Logical interface on which are created OSPF/LDP sessions, P2P IP

VLAN
-------------
name="vlan-100_DO_SKR_LAG-1_sfp1" mtu=1500 l2mtu=9582 mac-address=00:00:00:00:00:10 vlan-id=100 interface=sfp-sfpplus1 <- Main transmision

name="vlan-200_DO_SKR_LAG-2_sfp1" mtu=1500 l2mtu=9582 mac-address=00:00:00:00:00:10 vlan-id=200 interface=sfp-sfpplus1 <- Backup transmision

VPLS
-------------
add disabled=no l2mtu=1500 mtu=1500 mac-address=02:6A:29:21:7C:73 name=vpls-45_SINOLEKA_BIENIAK_AP_5_OMNI remote-peer=172.35.128.45 vpls-id=45:0

------------------------------------------------------------------------------------
And Config on OMNITIK AC which is connecting pppoe clients through VPLS to RB4011:
IP
-------------
add address=172.35.128.45 interface=Loopback network=172.35.128.45

MPLS
-------------
/mpls interface
set [ find default=yes ] mpls-mtu=1600
/mpls ldp
set enabled=yes lsr-id=172.35.128.45 transport-address=172.35.128.45
/mpls ldp accept-filter
add prefix=172.35.128.0/23
add prefix=172.16.128.0/23
add accept=no
/mpls ldp advertise-filter
add prefix=172.35.128.0/23
add prefix=172.16.128.0/23
add advertise=no
/mpls ldp interface
add interface=ether2

PHYSICAL IF
-------------
name="ether2" mtu=1500 l2mtu=2028

VPLS
-------------
l2mtu=1500 mtu=1500 mac-address=02:F8:D7:9F:31:F7 name=vpls-45_SINOLEKA_BIENIAK_AP_5_OMNI1 remote-peer=172.35.128.1 vpls-id=45:0

Please tell me how to setup L3MTU,L2MTU,MPLS MTU to avoid rx-too-long message on interfaces. I'm guessing that packets are fragmented. On packet-sniffer tool i can see sniffing sfp1 interface max MTU 1532. Should I set L3MTU to 1532 on all devices accress VPLS patch?
I have read it a lot in MUM articles and WIKI but didn't find solutions.

I Would appreciate any suggestions what I'm doing wrong.
Tom
 
georgekaskader
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Posts: 6
Joined: Wed Sep 11, 2019 5:26 pm

Re: VPLS MTU and interface errors RX-Too-long statistics

Sun Apr 11, 2021 11:40 pm

No One? Maybe support is here?
 
georgekaskader
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Posts: 6
Joined: Wed Sep 11, 2019 5:26 pm

Re: VPLS MTU and interface errors RX-Too-long statistics

Wed Apr 21, 2021 3:43 pm

Here is Mikrotik answer for my ticket. RB4011

Hello,

Thank you for sharing the details, we have reproduced the same results in our labs.

The powerbox device seems to count rx/tx-too-long on the SFP interface when packets are sent or received over 1515 bytes (including Ethernet header). It is only a counter error, packets are still correctly received and transmitted. We will try to improve the counter in the upcoming RouterOS releases.

As for the RB4011, the L2MTU on SFP1 with a 1Gbps rate seems to be wrongly set when a device is rebooted, thus it starts to drop and count rx-too-long packets. The L2MTU will start to limit correctly only when the SFP interface gets disabled/enabled. We will be looking forward to fix this issue as well.

Best regards,
Edgars P.

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