Jumbo Frame & IP MTU


Userlevel 2
Hi,

If I'm using "configure ip-mtu vlan" for specifying MTU size for a specific VLAN, should I use "enable jumbo-frame ports" for each port associated to that VLAN?

What is the relation with "configure jumbo-frame-size" if there are more than one tagged VLAN with different MTU on "configure ip-mtu vlan" with same associated ports?

Best regards,

4 replies

As per our implementation,"config ip-mtu size vlan" doesn't impact ipv4 jumbo frame data path traffic provided whether jumbo frame is enabled on ingress and egress L3 vlan ports using cmd "enable jumbo-frame ports".So, for fast path routing of ipv4 jumbo frame we need to enable jumbo-frame ports.

I believe there is no relation of "configure jumbo-frame size" with different L3 MTU for more than one tagged VLAN as for as ipv4 data path traffic is concerned .

L3 MTU size impact only l3 slow path traffic and some routing protocols.
Userlevel 6
enable jumbo-frame ports is for L2 switching of packets.
The IP-MTU setting on vlans is for L3 routing to route jumbo frames.

You cannot increase the ip-mtu without also enabling jumbo frames on the involved ports.
Userlevel 2
HI Oscar,

Can you give me some example of mixed tagged and untagged VLAN configuration of a port with different MTU for each VLAN (some with normal 1500 MTU)?

Best regards,
Userlevel 6
Just enable jumbo-frames on the ports, keep the default jumbo-frame size.
Then for each vlan you need to route bigger packets set the ip-mtu for that vlan to the value needed. Add the vlans to the ports.

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