Jumbo Frames Question - BSD

This is a discussion on Jumbo Frames Question - BSD ; Hi All, I am wondering what the story is with this (running the 4.2/i386 release) [root@nas ~]# route get 172.16.0.100 route to: networkservices destination: networkservices interface: em0 if address: gigabit-ethernet-gw flags: use hopcount mtu expire 1259 0 0 835 Why ...

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Thread: Jumbo Frames Question

  1. Jumbo Frames Question

    Hi All,

    I am wondering what the story is with this (running the 4.2/i386 release)

    [root@nas ~]# route get 172.16.0.100
    route to: networkservices
    destination: networkservices
    interface: em0
    if address: gigabit-ethernet-gw
    flags:
    use hopcount mtu expire
    1259 0 0 835

    Why is MTU 0?

    The story is I am using em interfaces at all ends on the LAN, all have
    their MTU set at 9000 and the gigabit switch I am using supports Jumbo
    frames.

    [root@nas ~]# ifconfig em0
    em0: flags=8843 mtu 9000
    lladdr 00:0e:0c:da:27:a1
    media: Ethernet autoselect (1000baseT full-duplex,master)
    status: active
    inet 172.16.0.254 netmask 0xffffff00 broadcast 172.16.0.255
    inet6 fe80::20e:cff:feda:27a1%em0 prefixlen 64 scopeid 0x1

    [root@nas ~]# route show
    Routing tables

    Internet:
    Destination Gateway Flags Refs Use Mtu
    Interface
    default c220-239-*-*.riv UGS 1 624 - em1
    loopback localhost UGRS 0 0 33208 lo0
    localhost localhost UH 4 144 33208 lo0
    172.16.0/24 link#1 UC 2 0 - em0
    networkservices 00:0d:61:43:2c:a5 UHLc 7 1674 - em0
    laptop 00:12:3f:14:66:74 UHLc 2 851 - em0

    Why do the routes for 172.16.0/24 and networkservices (172.16.0.100)
    have their MTU fields blank? What does this mean?


    From the other end, on a FreeBSD machine:

    [root@networkservices /var/log]# route get 172.16.0.254
    route to: gigabit-ethernet-gw.internal.schlossadler.net
    destination: gigabit-ethernet-gw.internal.schlossadler.net
    interface: em0
    flags:
    recvpipe sendpipe ssthresh rtt,msec rttvar hopcount mtu
    expire
    0 0 0 0 0 0 9000
    576

    As a 4GB file was being transferred across the LAN from this machine, I
    issued this command:

    [root@networkservices /home/alex]# netstat -m
    262/383/645 mbufs in use (current/cache/total)
    260/130/390/32768 mbuf clusters in use (current/cache/total/max)
    260/124 mbuf+clusters out of packet secondary zone in use (current/cache)
    0/0/0/0 4k (page size) jumbo clusters in use (current/cache/total/max)
    0/0/0/0 9k jumbo clusters in use (current/cache/total/max)
    0/0/0/0 16k jumbo clusters in use (current/cache/total/max)

    Surely I should expect to see more than 0's next to the jumbo frames. So
    this means they're not being used?

    Thanks

  2. Re: Jumbo Frames Question

    Any chance of getting a reply before christmas?


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