Why does vxlan_sys_4789 have a large MTU size
Environment
- OpenShift Container Platform 3
Issue
- We have the vxlan configured with an mtu of 1450 in the node configmaps for our servers. On ifconfig, we see a device called vxlan_sys_4789, which has a much larger MTU. Is this expected?
Resolution
- The large MTU is configured as expected as this interface acts as a tunnel between OCP nodes
Root Cause
- This interface encapsulates traffic with vxlan protocol so the packet going through the tunnel can be larger than the same packet once it's de-encapsulated, but since the vxlan encapsulates traffic generated in other interfaces (with "normal" mtu's) this isn't a problem
Diagnostic Steps
# ip addr show vxlan_sys_4789
123: vxlan_sys_4789: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65000 qdisc noqueue master ovs-system state UNKNOWN group default qlen 1000
link/ether 52:db:42:7b:2b:50 brd ff:ff:ff:ff:ff:ff
inet6 fe80::50db:42ff:fe7b:2b50/64 scope link
valid_lft forever preferred_lft forever
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