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Re: MTU on tun0



This is a ansible installer problem.

I had similar issue with my instalation and this is really important. Without MTU set to 1450 there is
a problem with traffic between nodes. I've spent four hours debugging our MySQL galera cluster on Nodes
which didn't want to synchronize but servers saw each other. It was due to MTU problem.



David Strejc
t: +420734270131

On Fri, Feb 12, 2016 at 9:37 AM, Per Carlson <pelle hemmop com> wrote:
Hi.

​We are seeing some strange packet traces on the nodes, and we suspect that it might be a MTU-issue.​

According to the documentation (https://docs.openshift.com/enterprise/3.1/install_config/configuring_sdn.html#configuring-the-pod-network-on-nodes) a "mtu" parameter in node-config.yaml should be reflected on the overlay network settings (tun0).

But on my hosts (OSE 3.1) that's not true:

master201
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

master202
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

master203
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

infra201
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

infra202
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1450

node201
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1450

node202
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1450

node203
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1450

node204
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

node205
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

node206
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

node207
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

node208
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

node209
   mtu: 1450
tun0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500


​[root master201 ~]# oc version
oc v3.1.0.4-16-g112fcc4
kubernetes v1.1.0-origin-1107-g4c8e6f4

BTW: we are using the mutitenant SDN.​

--
Pelle

Research is what I'm doing when I don't know what I'm doing.
- Wernher von Braun

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