Hi!
I wonder how can I enable jumbo frames on my new CRS504-4xq-in when I try to set the MTU to 9000 it does not accept it, I tried setting it in the bridge and on the interfaces booth did nto work.
According to the marketing material jumbo frames should be supported.
So how do I enable them?
On the PC side i have set 9000 and when using a cable from PC1 to PC2 it works.
But not through the switch.
Also when I run a benchmark I get 12 gbit/s at best 
Please advice.
If it looks like the device ‘does not accept’ your MTU, you are missing out some interface. to increase the MTU on a bridge, you need to increase it on all physical interface attached to that bridge as well.
I have a CRS504 here easily reaching near the 100gbit, if you are measuring noticeably less, it must have something to do with you configuration (traffic hitting the cpu, etc) or your way to measure (running speed test from the device itself, etc.)
You can share your configuration here for better feedback.
best
You need to first increase the L2MTU of all the ports that are members of the bridge first. Then you can increase the MTU on all those ports (you cannot set the MTU to be greater than L2MTU). The MTU of the bridge cannot exceed the smallest L2MTU of all its member ports.
Here is the config, do you see any obvious mistakes?
Also whats your method of benchmarking the performance?
# 2025-07-15 08:34:12 by RouterOS 7.19.3
#
# model = CRS504-4XQ
/interface bridge
add admin-mac=F4:1E:57:31:**:** auto-mac=no comment=defconf name=bridge
/ip pool
add name=dhcp_pool0 ranges=10.100.10.1-10.100.10.255
/ip dhcp-server
add address-pool=dhcp_pool0 interface=bridge lease-time=7h name=dhcp1
/port
set 0 name=serial0
/interface bridge port
add bridge=bridge comment=defconf interface=qsfp28-1-1
add bridge=bridge comment=defconf interface=qsfp28-1-2
add bridge=bridge comment=defconf interface=qsfp28-1-3
add bridge=bridge comment=defconf interface=qsfp28-1-4
add bridge=bridge comment=defconf interface=qsfp28-2-1
add bridge=bridge comment=defconf interface=qsfp28-2-2
add bridge=bridge comment=defconf interface=qsfp28-2-3
add bridge=bridge comment=defconf interface=qsfp28-2-4
add bridge=bridge comment=defconf interface=qsfp28-3-1
add bridge=bridge comment=defconf interface=qsfp28-3-2
add bridge=bridge comment=defconf interface=qsfp28-3-3
add bridge=bridge comment=defconf interface=qsfp28-3-4
add bridge=bridge comment=defconf interface=qsfp28-4-1
add bridge=bridge comment=defconf interface=qsfp28-4-2
add bridge=bridge comment=defconf interface=qsfp28-4-3
add bridge=bridge comment=defconf interface=qsfp28-4-4
/interface ovpn-server server
add mac-address=FE:3B:06:69:**:** name=ovpn-server1
/ip address
add address=10.100.3.15/16 comment=defconf interface=bridge network=\
10.100.0.0
/ip dhcp-client
add interface=ether1
/ip dhcp-server network
add address=10.100.0.0/16 gateway=10.100.3.15
/ip hotspot profile
set [ find default=yes ] html-directory=hotspot
/ip ipsec profile
set [ find default=yes ] dpd-interval=2m dpd-maximum-failures=5
/system clock
set time-zone-name=Europe/Vienna
/system routerboard settings
set enter-setup-on=delete-key
What I’m missing at first glance is L2MTU on the physical interfaces:
/interface ethernet
set [ find default-name=qsfp28-1-1 ] l2mtu=10218
set [ find default-name=qsfp28-1-2 ] l2mtu=10218
set [ find default-name=qsfp28-1-3 ] l2mtu=10218
set [ find default-name=qsfp28-1-4 ] l2mtu=10218
[...]
Another thing, if you are using a QSFP, lets say in port 1, only add interface qsfp28-1-1 to the bridge, leave the other interface enabled but otherwise unconfigured.
Could you may be provide your config for reference?
Also how to best test the performance with iperf3 i reach now 30gbit still a far cry from the 100 it should be able to do
Hi,
here is the relevant part of my config:
/interface bridge
add add-dhcp-option82=yes admin-mac=00:11:22:33:44:55 auto-mac=no dhcp-snooping=yes name=bridge port-cost-mode=short priority=0x4000 vlan-filtering=yes
/interface ethernet
set [ find default-name=qsfp28-1-1 ] auto-negotiation=no fec-mode=fec91 l2mtu=10218 mtu=9000 rx-flow-control=on tx-flow-control=on
set [ find default-name=qsfp28-1-2 ] l2mtu=10218
set [ find default-name=qsfp28-1-3 ] l2mtu=10218
set [ find default-name=qsfp28-1-4 ] l2mtu=10218
set [ find default-name=qsfp28-2-1 ] auto-negotiation=no fec-mode=fec91 l2mtu=10218 mtu=9000 rx-flow-control=on tx-flow-control=on
set [ find default-name=qsfp28-2-2 ] l2mtu=10218
set [ find default-name=qsfp28-2-3 ] l2mtu=10218
set [ find default-name=qsfp28-2-4 ] l2mtu=10218
set [ find default-name=qsfp28-3-1 ] auto-negotiation=no l2mtu=10218 mtu=9000 rx-flow-control=on speed=25G-baseCR tx-flow-control=on
set [ find default-name=qsfp28-3-2 ] l2mtu=10218 mtu=9000 rx-flow-control=on tx-flow-control=on
set [ find default-name=qsfp28-3-3 ] l2mtu=10218
set [ find default-name=qsfp28-3-4 ] l2mtu=10218
set [ find default-name=qsfp28-4-1 ] auto-negotiation=no fec-mode=off l2mtu=10218 mtu=9000 speed=10G-baseCR
set [ find default-name=qsfp28-4-2 ] auto-negotiation=no fec-mode=off l2mtu=10218 mtu=9000 speed=10G-baseCR
set [ find default-name=qsfp28-4-3 ] auto-negotiation=no l2mtu=10218 mtu=9000 rx-flow-control=on speed=10G-baseCR tx-flow-control=on
set [ find default-name=qsfp28-4-4 ] auto-negotiation=no fec-mode=off l2mtu=10218 mtu=9000 speed=10G-baseCR
/interface vlan
add interface=bridge name=MGMT vlan-id=8
/interface bonding
add mode=802.3ad mtu=9000 name="bond" slaves=qsfp28-3-1,qsfp28-3-2 transmit-hash-policy=layer-3-and-4
/interface ethernet switch qos priority-flow-control
add name=pfc-tc3 rx=yes traffic-class=3 tx=yes
/interface ethernet switch qos port
set qsfp28-1-1 egress-rate-queue3=100.0Gbps pfc=pfc-tc3 trust-l3=keep
set qsfp28-2-1 egress-rate-queue3=100.0Gbps pfc=pfc-tc3 trust-l3=keep
set qsfp28-3-1 egress-rate-queue3=25.0Gbps pfc=pfc-tc3 trust-l3=keep
set qsfp28-3-2 egress-rate-queue3=25.0Gbps pfc=pfc-tc3 trust-l3=keep
/interface ethernet switch qos profile
add name=roce traffic-class=3
add name=cnp traffic-class=6
/interface bridge port
add bridge=bridge interface=qsfp28-1-1 pvid=3
add bridge=bridge interface=qsfp28-2-1 pvid=3
add bridge=bridge trusted=yes
add bridge=bridge interface=qsfp28-4-1 trusted=yes
add bridge=bridge interface=qsfp28-4-2 trusted=yes
add bridge=bridge interface=qsfp28-4-3
/ip settings
set max-neighbor-entries=8192 tcp-syncookies=yes
/ipv6 settings
set accept-redirects=no accept-router-advertisements=no forward=no max-neighbor-entries=8192
/interface bridge vlan
add bridge=bridge tagged="qsfp28-1-1,bond,qsfp28-4-3" vlan-ids=1
add bridge=bridge tagged="qsfp28-2-1,bond,qsfp28-4-1,qsfp28-4-2" vlan-ids=2
add bridge=bridge vlan-ids=3
add bridge=bridge tagged="bond,qsfp28-4-1,qsfp28-4-2" vlan-ids=4
add bridge=bridge tagged="bond1,qsfp28-4-1,qsfp28-4-2" vlan-ids=5
add bridge=bridge tagged="bond,qsfp28-4-2" vlan-ids=6
add bridge=bridge tagged="bond,qsfp28-4-1,qsfp28-4-2" vlan-ids=7
add bridge=bridge tagged="bridge,bond,qsfp28-4-1,qsfp28-4-2,qsfp28-4-3" vlan-ids=8
add bridge=bridge tagged="bond,qsfp28-4-1,qsfp28-4-2" vlan-ids=9
add bridge=bridge tagged="bond,qsfp28-4-1,qsfp28-4-2" vlan-ids=10
/interface ethernet switch
set 0 qos-hw-offloading=yes
/interface ethernet switch qos map ip
add dscp=26 profile=roce
add dscp=48 profile=cnp
/interface ethernet switch qos tx-manager queue
set 1 schedule=high-priority-group weight=1
set 3 ecn=yes shared-pool-index=1 weight=1
/ip address
add address=1.2.3.4/24 interface=VLAN1 network=1.2.3.0
There is more to the config, but for cleanness I removed most of L3, custom scripts, etc.
[note: parts of the config are related to RoCE, don’t get confused (; ]
Regarding your performance testing, make sure to test from endpoint to endpoint (which i guess you are doing with iperf3) and also make sure you are not running into a TCP bottleneck, e.g. test with multiple parallel tcp connections (iperf3 -P 10 …) With that i do get close to 100gbit/s.
are you testing on windows or on linux?
I cant get more then 30 Gbe with iperf at its best, but when testing samba on a ramdisk with multiple clients i can get in total 60 Gbe so may be its a windows issue?
LOL windows suxxx… well windows client version, with a windows server to a windows server i can get 80-100 GBE with 10 iperf3 streams and 9000 mtu, on the exact same machines
Which Windows Server version did you test? It might be due to the default congestion control algorithm on older Windows Server versions (DCTCP) being different from the one the desktop versions (currently CUBIC).
2019 and 2022 work fine the problem happens if i use a client windows like win 11 education edition