Enabling jumbo frames with VLAN's



  • Hi

    What's the cleanest way to configure jumbo frames for my internal network connection?
    My Cisco router supports it. It already works on my NAS4Free box with also FreeBSD and the same NIC:

    Nas4Free:

    igb0: flags=8943 <up,broadcast,running,promisc,simplex,multicast>metric 0 mtu 9216
            options=6403bb <rxcsum,txcsum,vlan_mtu,vlan_hwtagging,jumbo_mtu,vlan_hwcsum,tso4,tso6,vlan_hwtso,rxcsum_ipv6,txcsum_ipv6></rxcsum,txcsum,vlan_mtu,vlan_hwtagging,jumbo_mtu,vlan_hwcsum,tso4,tso6,vlan_hwtso,rxcsum_ipv6,txcsum_ipv6></up,broadcast,running,promisc,simplex,multicast>

    Problems:

    1. I can't specify a size larger then 9000 bytes. I think my Cisco TODO supports 9216 bytes.
    2. I can't specify a size larger then the parent interface, but I have no option to configure the parent interface, I only see the VLAN interfaces?

    I could do configure a command like "ip link set eth1 mtu 9216" after boot, but it doesn't seem to be the nicest way on doing this?

    Screenshots:






  • LAYER 8 Global Moderator

    "2) I can't specify a size larger then the parent interface, but I have no option to configure the parent interface, I only see the VLAN interfaces?"

    Well go to the actual interface and you can adjust the mtu

    I really don't get the fascination with jumbo.. It really has little point other that really specific L2 vlans like a SAN or backup network where the devices talking to each other both support it..  So for example stuff like FCoE, NFS, iSCSI, vMotion can make use of it, but it really should stay on that L2..  Once you attempt to route it, all bets are off to be honest..  So if you want to create a SAN where your box has leg in that L2 to access your NAS ok.. But should really have another interface for all other traffic that will have to route..

    Even if bump the interface on pfsense, what traffic would be going to pfsense that wouldn't be routed to some other network, lets say the internet that sure and the hell has no jumbo support.  Your wireless network sure isn't going to use them.. So now your just going to have to fragment the shit out of any jumbo..  Which defeats whole purpose of the jumbo.

    So if you want to use it between devices on some L2, great can see some reason for traffic that moves large amounts of data.. But if the traffic is like a dns query, a http to some website, jumbo cause you more hurt then help.

    But sure good luck with it..




  • The problem is that I don't have the actual interface in my list? The "LAN" name is actually misleading: it's a VLAN (some dump for all trusted devices). You can see it in my first screenshot.

    But makes sense most of traffic is internet traffic. I have it on my NAS4Free and Kodi machines for example and those are connected with NFS.
    My Macbook Pro also has it (backups, moving files, etc..).

    But I though it was faster because you have less overhead over the cable (address, etc..) so more useful bytes and it needs to be unpacked anyhow because maybe internet has lower sizes or to get it fitted in a PPPoE packet. And it's running all on fast hardware.

    And from what I remember from my lessons is it only a MAXIMUM size. So if it needs to go to a network with a smaller MTU, it should never get in a big package anyhow, because they communicate about that?


  • LAYER 8 Global Moderator

    "I have it on my NAS4Free and Kodi machines for example"

    Well ok - then those devices should have their own private L2 that they use to talk to each other.. When talking to anything else they should use a normal network with standard mtu..

    You do have the interface its igb0, assign it to a opt interface.. Don't give it any IPs just set its mtu.  That is the parent, then you can adjust your vlans to use a mtu sized up to the max of what your parent as set too.

    "But I though it was faster because you have less overhead over the cable"

    It can be faster, until it has to be fragmented.. When once your going to route it most certainly will be.. Not sure where you got the idea its maximum size.. Yeah sure if you enabled jumbo on say a switch, it can pass smaller packets that are using smaller size.  But setup a box with mtu of 1500 on the same network and then set one as 9000 how well do they talk to each other? ;)  Sniff the traffic and see what happens.



  • Ok, will remove it on all machines then. Sounds clear!
    I had the idea from the name itself: maximum transmission unit


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