type: u32
help: Interface MTU
syntax:expression: $VAR(@) >= 1 && $VAR(@) <= 65535; "Must be between 1-65535"
val_help: u32:1-65535; Interface MTU

update: vtysh -c "configure terminal" -c "interface $IFNAME" -c "ipv6 ospf6 ifmtu $VAR(@)"
delete: vtysh -c "configure terminal" -c "interface $IFNAME" -c "no ipv6 ospf6 ifmtu"