Jumbo frame size set - netmtu in COROSYNC.CONF ?

L

leex12

Member
Mar 11, 2022
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Not sure if I was snow blind to them in v7 but since upgrade to v8 I have tons of messages 'complaining' about MTU size.

Historically I have had MTU set on NICs, bridges and vlans set to 9000.

Since seeing these messages I have validated 8745 seems to be a sweet spot working between nodes, VM, LXc and desktop clients using ping

Code: 
ping -M do -s 8745 pve06

Changed my MTU references to 8745 but the error didn't go away .. so I revised down and still didn't go away

Jun 16 12:16:56 pve01 corosync[1198]: [KNET ] pmtud: Starting PMTUD for host: 6 link: 1
Jun 16 12:16:56 pve01 corosync[1198]: [KNET ] udp: detected kernel MTU: 8517
Jun 16 12:16:56 pve01 corosync[1198]: [KNET ] pmtud: PMTUD completed for host: 6 link: 1 current link mtu: 8405
Jun 16 12:16:56 pve01 corosync[1198]: [KNET ] pmtud: Starting PMTUD for host: 3 link: 0
Jun 16 12:16:56 pve01 corosync[1198]: [KNET ] udp: detected kernel MTU: 8517
Jun 16 12:16:56 pve01 corosync[1198]: [KNET ] pmtud: PMTUD completed for host: 3 link: 0 current link mtu: 8405
Jun 16 12:16:56 pve01 corosync[1198]: [KNET ] pmtud: Starting PMTUD for host: 3 link: 1
Jun 16 12:16:56 pve01 corosync[1198]: [KNET ] udp: detected kernel MTU: 8517
Jun 16 12:16:56 pve01 corosync[1198]: [KNET ] pmtud: PMTUD completed for host: 3 link: 1 current link mtu: 8405
Jun 16 12:16:56 pve01 corosync[1198]: [KNET ] pmtud: Starting PMTUD for host: 1 link: 0
Jun 16 12:16:56 pve01 corosync[1198]: [KNET ] udp: detected kernel MTU: 8517

I have left the NICs set to 8745 but now have the bridges etc set to 8517. Having reduced the MTU size a couple of times and it not resolving the issue I feel I changing the wrong thing.

Are people setting the netmtu to force the MTU size? I currently don't have this entry in my corosync.conf
 
AFAIK, the `netmtu` setting has no effect in Corosync 3 using knet as the transport (Which is default since Corosync 3 / Proxmox VE 6). Can't tell why you're getting messages since v8.

Would you mind posting your corosync.conf? Did you try removing the netmtu setting from the config?
 
my question was shouls i be setting netmtu to stop the messages!

There is nothing exciting in my config

Code: 
logging {
  debug: on
  to_syslog: yes
}

nodelist {
  node {
    name: pve01
    nodeid: 5
    quorum_votes: 1
    ring0_addr: 192.168.20.1
    ring1_addr: 10.107.0.1
  }
  node {
    name: pve02
    nodeid: 4
    quorum_votes: 1
    ring0_addr: 192.168.20.2
    ring1_addr: 10.107.0.2
  }
  node {
    name: pve03
    nodeid: 2
    quorum_votes: 1
    ring0_addr: 192.168.20.3
    ring1_addr: 10.107.0.3
  }
  node {
    name: pve04
    nodeid: 1
    quorum_votes: 1
    ring0_addr: 192.168.20.4
    ring1_addr: 10.107.0.4
  }
  node {
    name: pve05
    nodeid: 3
    quorum_votes: 1
    ring0_addr: 192.168.20.5
    ring1_addr: 10.107.0.5
  }
  node {
    name: pve06
    nodeid: 6
    quorum_votes: 1
    ring0_addr: 192.168.20.6
    ring1_addr: 10.107.0.6
  }
}

quorum {
  provider: corosync_votequorum
}

totem {
  cluster_name: x12
  config_version: 27
  interface {
    linknumber: 0
  }
  interface {
    linknumber: 1
  }
  ip_version: ipv4-6
  link_mode: passive
  secauth: on
  version: 2
}
 
i have moved everything back to 8745
Code: 
Jun 18 18:38:44 pve01 corosync[1262]:   [KNET  ] pmtud: PMTUD completed for host: 2 link: 0 current link mtu: 8629
Jun 18 18:38:44 pve01 corosync[1262]:   [KNET  ] pmtud: Starting PMTUD for host: 2 link: 1
Jun 18 18:38:44 pve01 corosync[1262]:   [KNET  ] udp: detected kernel MTU: 8745

just seems like what ever I set the mtu to it wants it to be a hundred or so smaller.
 
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